LM3488MMX/NOPB - NATIONAL SEMICONDUCTOR

Product

Folder

Order

Now

Technical

Documents

Tools &

Software

Support &

Community

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

LM3488/-Q1 Automotive High-Efficiency Controller for Boost, SEPIC and Fly-Back DC-DC

Converters

1 Features

1• Automotive Grade Product, AEC-Q100 Qualified

• 8-Lead VSSOP Package

• Internal Push-Pull Driver With 1-A Peak Current

Capability

• Current Limit and Thermal Shutdown

• Frequency Compensation Optimized With a

Capacitor and a Resistor

• Internal Soft-Start

• Current Mode Operation

• Undervoltage Lockout With Hysteresis

• Key Specifications:

– Wide Supply Voltage Range of 2.97 V to 40 V

– 100-kHz to 1-MHz Adjustable and

Synchronizable Clock Frequency

– ±1.5% (Overtemperature) Internal Reference

– 5-µA Shutdown Current (Overtemperature)

• Create a Custom Design Using the LM3488 with

the WEBENCH Power Designer

2 Applications

• Automotive Start-Stop Applications

• Automotive ADAS Driver Information

• One Cell/Two Cell Li-ion Battery Powered

Portable Bluetooth Audio Systems

• Notebooks, PDAs, Digital Cameras, and other

Portable Applications

• Offline Power Supplies

• Set-Top Boxes

• Boost for Audio Amplifiers

3 Description

The LM3488 is a versatile low-side N-FET high-

performance controller for switching regulators. This

device is suitable for use in topologies requiring low-

side FET, such as boost, flyback, or SEPIC.

Moreover, the LM3488 can be operated at extremely

high switching frequency to reduce the overall

solution size. The switching frequency of LM3488 can

be adjusted to any value from 100 kHz to 1 MHz by

using a single external resistor or by synchronizing it

to an external clock. Current mode control provides

superior bandwidth and transient response, besides

cycle-by-cycle current limiting. Output current can be

programmed with a single external resistor.

The LM3488 has built-in features such as thermal

shutdown, short-circuit protection, and overvoltage

protection. Power-saving shutdown mode reduces the

total supply current to 5 µA and allows power supply

sequencing. Internal soft-start limits the inrush current

at start-up.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

LM3488 VSSOP (8) 3.00 mm × 3.00 mm

LM3488-Q1

(1) For all available packages, see the orderable addendum at

the end of the datasheet.

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Typical SEPIC Converter

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Table of Contents

1 Features.................................................................. 1

2 Applications ........................................................... 1

3 Description............................................................. 1

4 Revision History..................................................... 3

5 Pin Configuration and Functions......................... 4

6 Specifications......................................................... 4

6.1 Absolute Maximum Ratings ..................................... 4

6.2 ESD Ratings : LM3488 ............................................. 4

6.3 ESD Ratings: LM3488-Q1 ........................................ 5

6.4 Recommended Operating Conditions....................... 5

6.5 Thermal Information.................................................. 5

6.6 Electrical Characteristics........................................... 5

6.7 Typical Characteristics.............................................. 8

7 Detailed Description............................................ 12

7.1 Overview................................................................. 12

7.2 Functional Block Diagram....................................... 13

7.3 Feature Description................................................. 13

7.4 Device Functional Modes........................................ 17

8 Application and Implementation ........................ 18

8.1 Application Information............................................ 18

8.2 Typical Applications ................................................ 18

9 Power Supply Recommendations...................... 30

10 Layout................................................................... 30

10.1 Layout Guidelines ................................................. 30

10.2 Layout Example .................................................... 31

11 Device and Documentation Support................. 31

11.1 Custom Design with WEBENCH Tools................. 31

11.2 Receiving Notification of Documentation Updates 32

11.3 Related Links ........................................................ 32

11.4 Trademarks........................................................... 32

11.5 Electrostatic Discharge Caution............................ 32

11.6 Glossary................................................................ 32

12 Mechanical, Packaging, and Orderable

Information........................................................... 32

4 Revision History

Changes from Revision N (December 2014) to Revision O Page

• Changed Datasheet title ........................................................................................................................................................ 1

• Changed Handling Ratings to ESD Ratings .......................................................................................................................... 5

Changes from Revision M (March 2013) to Revision N Page

• Added Pin Configuration and Functions section, Handling Rating table, Feature Description section, Device

Functional Modes,Application and Implementation section, Power Supply Recommendations section, Layout

section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information

section ................................................................................................................................................................................... 1

• Changed ESD Table and Features section............................................................................................................................ 1

• Changed application information. .......................................................................................................................................... 1

Changes from Revision L (March 2013) to Revision M Page

• Changed layout of National Data Sheet to TI format .......................................................................................................... 32

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

5 Pin Configuration and Functions

8-Pin DGK

VSSOP Package

Top View

Pin Functions

PIN TYPE DESCRIPTION

NAME NO.

ISEN 1 I Current sense input pin. Voltage generated across an external sense resistor is fed into this pin.

COMP 2 A Compensation pin. A resistor, capacitor combination connected to this pin provides compensation for

the control loop.

FB 3 I Feedback pin. The output voltage should be adjusted using a resistor divider to provide 1.26 V at this

pin.

AGND 4 P Analog ground pin.

PGND 5 P Power ground pin.

DR 6 O Drive pin of the IC. The gate of the external MOSFET should be connected to this pin.

FA/SYNC/SD 7 A Frequency adjust, synchronization, and Shutdown pin. A resistor connected to this pin sets the

oscillator frequency. An external clock signal at this pin will synchronize the controller to the frequency

of the clock. A high level on this pin for ≥30 µs will turn the device off. The device will then draw less

than 10µA from the supply.

VIN 8 P Power supply input pin.

(1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Recommended Operating Conditions are

conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical

Characteristics.

6 Specifications

6.1 Absolute Maximum Ratings (1)

MIN MAX UNIT

Input voltage 45 V

FB pin voltage –0.4 < VFB VFB < 7 V

FA/SYNC/SD pin voltage –0.4 < VFA/SYNC/SD VFA/SYNC/SD < 7 V

Peak driver output current (< 10 µs) 1 A

Power dissipation Internally Limited

Junction temperature 150 °C

Lead temperature Vapor Phase (60 s) 215 °C

Infared (15 s) 260 °C

DR pin voltage −0.4 ≤VDR VDR ≤8 V

ILIM pin voltage 600 mV

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

6.2 ESD Ratings : LM3488 MIN MAX UNIT

V(ESD) Electrostatic discharge

Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all

pins(1) –2000 2000

Charged device model (CDM), per JEDEC specification

JESD22-C101, all pins(2) –750 750

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

(1) AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification.

6.3 ESD Ratings: LM3488-Q1 MIN MAX UNIT

V(ESD) Electrostatic discharge

Human body model (HBM), per AEC Q100-002(1) –2000 2000

Charged device model (CDM), per

AEC Q100-011

Corner pins (1, 4, 5,

and 8) –750 750

Other pins –750 750

6.4 Recommended Operating Conditions MIN MAX UNIT

Supply Voltage 2.97 ≤VIN VIN ≤40 V

Junction Temperature Range −40 ≤TJTJ≤125 °C

Switching Frequency 100 ≤FSW FSW ≤1 kHz/MH

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

6.5 Thermal Information

THERMAL METRIC(1)

LM3488,

LM3488-Q1 UNIT

DGK

8 PINS

RθJA Junction-to-ambient thermal resistance 160

°C/W

RθJC(top) Junction-to-case (top) thermal resistance 50

RθJB Junction-to-board thermal resistance 77

ψJT Junction-to-top characterization parameter 4.7

ψJB Junction-to-board characterization parameter 76

(1) The voltage on the drive pin, VDR is equal to the input voltage when input voltage is less than 7.2 V. VDR is equal to 7.2 V when the

input voltage is greater than or equal to 7.2 V.

(2) The limits for the maximum duty cycle can not be specified since the part does not permit less than 100% maximum duty cycle

operation.

6.6 Electrical Characteristics

Unless otherwise specified, VIN = 12 V, RFA = 40 kΩ, TJ= 25°C

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

VFB Feedback Voltage VCOMP = 1.4 V, 2.97 ≤VIN ≤40 V 1.2507 1.26 1.2753 V

VCOMP = 1.4 V, 2.97 ≤VIN ≤40 V,

−40°C ≤TJ≤125°C 1.24 1.28

ΔVLINE Feedback Voltage Line Regulation 2.97 ≤VIN ≤40 V 0.001 %/V

ΔVLOAD Output Voltage Load Regulation IEAO Source/Sink ±0.5 %/V

(max)

VUVLO Input Undervoltage Lock-out 2.85 V

−40°C ≤TJ≤125°C 2.97

VUV(HYS) Input Undervoltage Lock-out Hysteresis 170 mV

−40°C ≤TJ≤125°C 130 210

Fnom Nominal Switching Frequency RFA = 40 KΩ400 kHz

RFA = 40 KΩ,−40°C ≤TJ≤125°C 360 430

RDS1 (ON) Driver Switch On Resistance (top) IDR = 0.2A, VIN= 5 V 16 Ω

RDS2 (ON) Driver Switch On Resistance (bottom) IDR = 0.2A 4.5 Ω

VDR (max) Maximum Drive Voltage Swing(1) VIN < 7.2 V VIN V

VIN ≥7.2 V 7.2

Dmax Maximum Duty Cycle(2) 100%

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Electrical Characteristics (continued)

Unless otherwise specified, VIN = 12 V, RFA = 40 kΩ, TJ= 25°C

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

(3) For this test, the FA/SYNC/SD Pin is pulled to ground using a 40K resistor .

(4) For this test, the FA/SYNC/SD Pin is pulled to 5 V using a 40K resistor.

(5) The over-voltage protection is specified with respect to the feedback voltage. This is because the over-voltage protection tracks the

feedback voltage. The over-voltage thresold can be calculated by adding the feedback voltage, VFB to the over-voltage protection

specification.

Tmin (on) Minimum On Time 325 nsec

−40°C ≤TJ≤125°C 230 550

ISUPPLY Supply Current (switching) See (3) 2.7 mA

See (3),−40°C ≤TJ≤125°C 3.0

IQQuiescent Current in Shutdown Mode VFA/SYNC/SD = 5 V(4), VIN = 5 V 5 µA

VFA/SYNC/SD = 5 V(4), VIN = 5 V,

−40°C ≤TJ≤125°C 7

VSENSE Current Sense Threshold Voltage VIN = 5 V 135 156 180 mV

VIN = 5 V, −40°C ≤TJ≤125°C 125 190

VSC Short-Circuit Current Limit Sense Voltage VIN = 5 V 343 mV

VIN = 5 V, −40°C ≤TJ≤125°C 250 415

VSL Internal Compensation Ramp Voltage VIN = 5 V 92 mV

VIN = 5 V, −40°C ≤TJ≤125°C 52 132

VSL ratio VSL/VSENSE 0.30 0.49 0.70

VOVP Output Overvoltage Protection (with

respect to feedback voltage) (5) VCOMP = 1.4 V 32 50 78 mV

VCOMP = 1.4 V, −40°C ≤TJ≤

125°C 25 85

VOVP(HYS) Output Over-Voltage Protection

Hysteresis(5) VCOMP = 1.4 V 60 mV

VCOMP = 1.4 V, −40°C ≤TJ≤

125°C 20 110

Gm Error Ampifier Transconductance VCOMP = 1.4 V, IEAO = 100 µA

(Source/Sink) 600 800 1000 µmho

VCOMP = 1.4 V, IEAO = 100 µA

(Source/Sink), −40°C ≤TJ≤125°C 365 1265

AVOL Error Amplifier Voltage Gain VCOMP = 1.4 V, IEAO = 100 µA

(Source/Sink) 38 V/V

VCOMP = 1.4 V, IEAO = 100 µA

(Source/Sink), −40°C ≤TJ≤125°C 26 44

IEAO Error Amplifier Output Current (Source/

Sink) Source, VCOMP = 1.4 V, VFB = 0 V 80 110 140 µA

Source, VCOMP = 1.4 V, VFB = 0 V,

−40°C ≤TJ≤125°C 50 180

Sink, VCOMP = 1.4 V, VFB = 1.4 V −100 −140 −180 µA

Sink, VCOMP = 1.4 V, VFB = 1.4 V,

−40°C ≤TJ≤125°C −85 −185

VEAO Error Amplifier Output Voltage Swing Upper Limit: VFB = 0 V, COMP Pin

= Floating 2.2 V

Upper Limit: VFB = 0 V, COMP Pin

= Floating, −40°C ≤TJ≤125°C 1.8 2.4

Lower Limit: VFB = 1.4 V 0.56 V

Lower Limit: VFB = 1.4 V, −40°C ≤

TJ≤125°C 0.2 1.0

TSS Internal Soft-Start Delay VFB = 1.2 V, VCOMP = Floating 4 ms

TrDrive Pin Rise Time Cgs = 3000 pf, VDR = 0 to 3 V 25 ns

TfDrive Pin Fall Time Cgs = 3000 pf, VDR = 0 to 3 V 25 ns

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Electrical Characteristics (continued)

Unless otherwise specified, VIN = 12 V, RFA = 40 kΩ, TJ= 25°C

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

(6) The FA/SYNC/SD pin should be pulled to VIN through a resistor to turn the regulator off.

VSD Shutdown and Synchronization signal

threshold (6) Output = High 1.27 V

Output = High, −40°C ≤TJ≤125°C 1.4

Output = Low 0.65 V

Output = Low, −40°C ≤TJ≤125°C 0.3

ISD Shutdown Pin Current VSD = 5 V −1 µA

VSD = 0 V +1

IFB Feedback Pin Current 15 nA

TSD Thermal Shutdown 165 °C

Tsh Thermal Shutdown Hysteresis 10 °C

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

6.7 Typical Characteristics

Unless otherwise specified, VIN = 12V, TJ= 25°C.

Figure 1. IQvs Temperature & Input Voltage Figure 2. ISupply vs Input Voltage (Non-Switching)

Figure 3. ISupply vs VIN Figure 4. Switching Frequency vs RFA

Figure 5. Frequency vs Temperature Figure 6. Drive Voltage vs Input Voltage

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Typical Characteristics (continued)

Unless otherwise specified, VIN = 12V, TJ= 25°C.

Figure 7. Current Sense Threshold vs Input Voltage Figure 8. COMP Pin Voltage vs Load Current

Figure 9. Efficiency vs Load Current (3.3 V In and 12 V Out) Figure 10. Efficiency vs Load Current (5 V In and 12 V Out)

Figure 11. Efficiency vs Load Current (9 V In and 12 V Out) Figure 12. Efficiency vs Load Current (3.3 V In and 5 V Out)

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Typical Characteristics (continued)

Unless otherwise specified, VIN = 12V, TJ= 25°C.

Figure 13. Error Amplifier Gain Figure 14. Error Amplifier Phase

Figure 15. COMP Pin Source Current vs Temperature Figure 16. Short Circuit Protection vs Input Voltage

Figure 17. Compensation Ramp vs Compensation Resistor Figure 18. Shutdown Threshold Hysteresis vs Temperature

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Typical Characteristics (continued)

Unless otherwise specified, VIN = 12V, TJ= 25°C.

Figure 19. Current Sense Voltage vs Duty Cycle

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

7 Detailed Description

7.1 Overview

The LM3488 uses a fixed frequency, Pulse Width Modulated (PWM), current mode control architecture. In a

typical application circuit, the peak current through the external MOSFET is sensed through an external sense

resistor. The voltage across this resistor is fed into the ISEN pin. This voltage is then level shifted and fed into the

positive input of the PWM comparator. The output voltage is also sensed through an external feedback resistor

divider network and fed into the error amplifier negative input (feedback pin, FB). The output of the error amplifier

(COMP pin) is added to the slope compensation ramp and fed into the negative input of the PWM comparator.

At the start of any switching cycle, the oscillator sets the RS latch using the SET/Blank-out and switch logic

blocks. This forces a high signal on the DR pin (gate of the external MOSFET) and the external MOSFET turns

on. When the voltage on the positive input of the PWM comparator exceeds the negative input, the RS latch is

reset and the external MOSFET turns off.

The voltage sensed across the sense resistor generally contains spurious noise spikes, as shown in Figure 20.

These spikes can force the PWM comparator to reset the RS latch prematurely. To prevent these spikes from

resetting the latch, a blank-out circuit inside the IC prevents the PWM comparator from resetting the latch for a

short duration after the latch is set. This duration is about 150ns and is called the blank-out time.

Under extremely light load or no-load conditions, the energy delivered to the output capacitor when the external

MOSFET is on during the blank-out time is more than what is delivered to the load. An over-voltage comparator

inside the LM3488 prevents the output voltage from rising under these conditions. The over-voltage comparator

senses the feedback (FB pin) voltage and resets the RS latch under these conditions. The latch remains in reset

state till the output decays to the nominal value.

Figure 20. Basic Operation of the PWM Comparator

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Slope Compensation Ramp

The LM3488 uses a current mode control scheme. The main advantages of current mode control are inherent

cycle-by-cycle current limit for the switch, and simpler control loop characteristics. It is also easy to parallel power

stages using current mode control since as current sharing is automatic.

Current mode control has an inherent instability for duty cycles greater than 50%, as shown in Figure 21. In

Figure 21, a small increase in the load current causes the switch current to increase by ΔIO. The effect of this

load change, ΔI1, is :

(1)

From the above equation, when D > 0.5, ΔI1will be greater than ΔIO. In other words, the disturbance is divergent.

So a very small perturbation in the load will cause the disturbance to increase.

To prevent the sub-harmonic oscillations, a compensation ramp is added to the control signal, as shown in

Figure 22.

'MC = 40x10-6 . RSL . FS

RSEN

Amps

second

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Feature Description (continued)

With the compensation ramp,

(2)

Figure 21. Sub-Harmonic Oscillation for D>0.5

Figure 22. Compensation Ramp Avoids Sub-Harmonic Oscillation

The compensation ramp has been added internally in LM3488. The slope of this compensation ramp has been

selected to satisfy most of the applications. The slope of the internal compensation ramp depends on the

frequency. This slope can be calculated using the formula:

MC= VSL.FSVolts/second (3)

In the above equation, VSL is the amplitude of the internal compensation ramp. Limits for VSL have been specified

in the electrical characteristics.

In order to provide the user additional flexibility, a patented scheme has been implemented inside the IC to

increase the slope of the compensation ramp externally, if the need arises. Adding a single external resistor,

RSL(as shown in Figure 23) increases the slope of the compensation ramp, MCby :

(4)

In this equation, ΔVSL is equal to 40.10-6RSL. Hence,

(5)

ΔVSL versus RSL has been plotted in Figure 24 for different frequencies.

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Feature Description (continued)

Figure 23. Increasing the Slope of the Compensation Ramp

Figure 24. ΔVSL vs RSL

7.3.2 Frequency Adjust/Synchronization/Shutdown

The switching frequency of LM3488 can be adjusted between 100kHz and 1MHz using a single external resistor.

This resistor must be connected between FA/SYNC/SD pin and ground, as shown in Figure 25. See Typical

Characteristics to determine the value of the resistor required for a desired switching frequency.

The LM3488 can be synchronized to an external clock. The external clock must be connected to the

FA/SYNC/SD pin through a resistor, RSYNC as shown in Figure 26. The value of this resistor is dependent on the

off time of the synchronization pulse, TOFF(SYNC).Table 1 shows the range of resistors to be used for a given

TOFF(SYNC).

Table 1. Recommended Series Resistance for

Synchronization

TOFF(SYNC) (µs) RSYNC range (kΩ)

1 5 to 13

2 20 to 40

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Table 1. Recommended Series Resistance for

Synchronization (continued)

TOFF(SYNC) (µs) RSYNC range (kΩ)

3 40 to 65

4 55 to 90

5 70 to 110

6 85 to 140

7 100 to 160

8 120 to 190

9 135 to 215

10 150 to 240

It is also necessary to have the width of the synchronization pulse wider than the duty cycle of the converter

(when DR pin is high and the switching point is low). It is also necessary to have the synchronization pulse width

≥300nsecs.

The FA/SYNC/SD pin also functions as a shutdown pin. If a high signal (see Electrical Characteristics for

definition of high signal) appears on the FA/SYNC/SD pin, the LM3488 stops switching and goes into a low

current mode. The total supply current of the IC reduces to less than 10µA under these conditions.

Figure 27 and Figure 28 show implementation of shutdown function when operating in Frequency adjust mode

and synchronization mode respectively. In frequency adjust mode, connecting the FA/SYNC/SD pin to ground

forces the clock to run at a certain frequency. Pulling this pin high shuts down the IC. In frequency adjust or

synchronization mode, a high signal for more than 30µs shuts down the IC.

Figure 29 shows implementation of both frequency adjust with RFA resistor and frequency synchronization with

RSYNC. The switching frequency is defined by RFA when a synchronization signal is not applied. When sync is

applied it overrides the RFA setting.

Figure 25. Frequency Adjust

Figure 26. Frequency Synchronization

LM3488

FA/SYNC/SD

RFA

RSYNC CSYNC

270 pF

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Figure 27. Shutdown Operation in Frequency Adjust Mode

Figure 28. Shutdown Operation in Synchronization Mode

Figure 29. Frequency Adjust or Frequency Synchronization

7.3.3 Short-Circuit Protection

When the voltage across the sense resistor (measured on ISEN Pin) exceeds 350mV, short-circuit current limit

gets activated. A comparator inside LM3488 reduces the switching frequency by a factor of 5 and maintains this

condition till the short is removed.

7.4 Device Functional Modes

The device is set to run as soon as the input voltage crosses above the UVLO set point and at a frequency set

according to the FA/SYNC/SD pin pull-down resistor or to run at a frequency set by the waveform applied to the

FA/SYNC/SD pin.

If the FA/SYNC/SD pin is pulled high, the LM3488 enters shut-down mode.

If the voltage at the ISEN pin exceeds Vsc, the device enters short-circuit protection mode.

20k

RF1

CC 22 nF

4.7k

AGND

COMP

ISEN RFA

40k

VIN

FA/SD/SYNC

PGND

10 PH

0.025:

RSN

IRF7807

D MBRD340

CIN

100 PF, 6.3V

VIN = 3.3V (±10%)

60k

RF2

COUT

100 PF, 10V

VOUT = 5V, 2A

CSN

0.01 PF

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM3488 may be operated in either continuous or discontinuous conduction mode. The following applications

are designed for continuous conduction operation. This mode of operation has higher efficiency and lower EMI

characteristics than the discontinuous mode.

8.2 Typical Applications

8.2.1 Boost Converter

Figure 30. Typical High Efficiency Step-Up (Boost) Converter

The most common topology for LM3488 is the boost or step-up topology. The boost converter converts a low

input voltage into a higher output voltage. The basic configuration for a boost regulator is shown in Figure 31. In

continuous conduction mode (when the inductor current never reaches zero at steady state), the boost regulator

operates in two cycles. In the first cycle of operation, MOSFET Q is turned on and energy is stored in the

inductor. During this cycle, diode D is reverse biased and load current is supplied by the output capacitor, COUT.

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Typical Applications (continued)

Figure 31. Simplified Boost Converter Diagram

(a) First cycle of operation

(b) Second cycle of operation

In the second cycle, MOSFET Q is off and the diode is forward biased. The energy stored in the inductor is

transferred to the load and output capacitor. The ratio of these two cycles determines the output voltage. The

output voltage is defined as:

(6)

(ignoring the drop across the MOSFET and the diode), or

where

• D is the duty cycle of the switch

• VDis the forward voltage drop of the diode

• VQis the drop across the MOSFET when it is on (7)

8.2.1.1 Design Requirements

To calculate component values for a Boost converter, the power supply parameters shown in Table 2 should be

known. The design shown in Figure 30 is the result of starting with example values shown in Table 2.

Table 2. Boost Design Parameters

DESIGN PARAMETER EXAMPLE VALUE

Input voltage range 3V to 3.6V

Output voltage 5V

Maximum current 2A

Operating frequency 350kHz

t (s)

IL_AVG

ISW_AVG

D*Ts Ts

IL (A)

ID (A)

VIN LVV OUTIN 

LVV OUTIN -

(a)

(b)

ISW (A)

(C)

ID_AVG

=IOUT_AVG

t (s)

D*Ts Ts

VIN

'iL

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Custom Design with WEBENCH Tools

Click here to create a custom design using the LM3488 device with the WEBENCH®Power Designer.

1. Start by entering your VIN, VOUT and IOUT requirements.

2. Optimize your design for key parameters like efficiency, footprint and cost using the optimizer dial and

compare this design with other possible solutions from Texas Instruments.

3. WEBENCH Power Designer provides you with a customized schematic along with a list of materials with real

time pricing and component availability.

4. In most cases, you will also be able to:

– Run electrical simulations to see important waveforms and circuit performance,

– Run thermal simulations to understand the thermal performance of your board,

– Export your customized schematic and layout into popular CAD formats,

– Print PDF reports for the design, and share your design with colleagues.

5. Get more information about WEBENCH tools at www.ti.com/webench.

8.2.1.2.2 Power Inductor Selection

The inductor is one of the two energy storage elements in a boost converter. Figure 32 shows how the inductor

current varies during a switching cycle. The current through an inductor is quantified as:

(8)

Figure 32. A. Inductor Current B. Diode Current C. Switch Current

VOUT = 1.26(

1+RF1

RF2

(

2fSL

'iL = DVIN

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

If VL(t) is constant, diL(t)/dt must be constant. Hence, for a given input voltage and output voltage, the current in

the inductor changes at a constant rate.

The important quantities in determining a proper inductance value are IL(the average inductor current) and ΔiL

(the inductor current ripple). If ΔiLis larger than IL, the inductor current will drop to zero for a portion of the cycle

and the converter will operate in discontinuous conduction mode. If ΔiLis smaller than IL, the inductor current will

stay above zero and the converter will operate in continuous conduction mode. All the analysis in this datasheet

assumes operation in continuous conduction mode. To operate in continuous conduction mode, the following

conditions must be met:

IL>ΔiL(9)

(10)

(11)

Choose the minimum IOUT to determine the minimum L. A common choice is to set ΔiLto 30% of IL. Choosing an

appropriate core size for the inductor involves calculating the average and peak currents expected through the

inductor. In a boost converter,

(12)

and IL_peak = IL(max) + ΔiL(max),

where

(13)

A core size with ratings higher than these values should be chosen. If the core is not properly rated, saturation

will dramatically reduce overall efficiency.

The LM3488 can be set to switch at very high frequencies. When the switching frequency is high, the converter

can be operated with very small inductor values. With a small inductor value, the peak inductor current can be

extremely higher than the output currents, especially under light load conditions.

The LM3488 senses the peak current through the switch. The peak current through the switch is the same as the

peak current calculated above.

8.2.1.2.3 Programming the Output Voltage

The output voltage can be programmed using a resistor divider between the output and the feedback pins, as

shown in Figure 33. The resistors are selected such that the voltage at the feedback pin is 1.26V. RF1 and RF2

can be selected using the equation,

(14)

A 100-pF capacitor may be connected between the feedback and ground pins to reduce noise.

RSEN = VSENSE - (D x VSENSE x VSLratio)

ISWLIMIT

ISWLIMIT = IOUT

(1-D) +(D x VIN)

(2 x fS x L)

RSEN = VSENSE - (D x VSL)

ISWLIMIT

VOUT

ISEN

COUT

Rfb2

VIN

LM3488

RSEN

Rfb1

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Figure 33. Adjusting the Output Voltage

8.2.1.2.4 Setting the Current Limit

The maximum amount of current that can be delivered to the load is set by the sense resistor, RSEN. Current limit

occurs when the voltage that is generated across the sense resistor equals the current sense threshold voltage,

VSENSE. When this threshold is reached, the switch will be turned off until the next cycle. Limits for VSENSE are

specified in Electrical Characteristics. VSENSE represents the maximum value of the internal control signal VCS.

This control signal, however, is not a constant value and changes over the course of a period as a result of the

internal compensation ramp (see Figure 20). Therefore the current limit threshold will also change. The actual

current limit threshold is a function of the sense voltage (VSENSE) and the internal compensation ramp:

RSEN x ISWLIMIT = VCSMAX = VSENSE - (D x VSL)

where

• ISWLIMIT is the peak switch current limit, defined by the equation below. As duty cycle increases, the control

voltage is reduced as VSL ramps up. Since current limit threshold varies with duty cycle, the following equation

should be used to select RSEN and set the desired current limit threshold: (15)

(16)

The numerator of the above equation is VCS, and ISWLIMIT is calculated as:

(17)

To avoid false triggering, the current limit value should have some margin above the maximum operating value,

typically 120%. Values for both VSENSE and VSL are specified in Electrical Characteristics. However, calculating

with the limits of these two specs could result in an unrealistically wide current limit or RSEN range. Therefore, the

following equation is recommended, using the VSL ratio value given in Electrical Characteristics:

(18)

RSL > 40 PA

RSEN x (Vo - 2VIN)

2 x fS x L - VSL

RSEN < 2 x VSL x fS x L

Vo - (2 x VIN)

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

RSEN is part of the current mode control loop and has some influence on control loop stability. Therefore, once

the current limit threshold is set, loop stability must be verified. To verify stability, use the following equation:

(19)

If the selected RSEN is greater than this value, additional slope compensation must be added to ensure stability,

as described in Current Limit with External Slope Compensation.

8.2.1.2.5 Current Limit with External Slope Compensation

RSL is used to add additional slope compensation when required. It is not necessary in most designs and RSL

should be no larger than necessary. Select RSL according to the following equation:

where

• RSEN is the selected value based on current limit. With RSL installed, the control signal includes additional

external slope to stabilize the loop, which will also have an effect on the current limit threshold. Therefore, the

current limit threshold must be re-verified, as illustrated in the equations below : (20)

VCS = VSENSE – (D x (VSL +ΔVSL))

where

•ΔVSL is the additional slope compensation generated and calculated as: (21)

ΔVSL = 40 µA x RSL (22)

RSEN = VSENSE

Vo - Vi

L x fS x D

ISWLIMIT +

ISWLIMIT = VSENSE - (D x(VSL + 'VSL))

RSEN

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

This changes the equation for current limit (or RSEN) to:

(23)

The RSEN and RSL values may have to be calculated iteratively in order to achieve both the desired current limit

and stable operation. In some designs RSL can also help to filter noise on the ISEN pin.

If the inductor is selected such that ripple current is the recommended 30% value, and the current limit threshold

is 120% of the maximum peak, a simpler method can be used to determine RSEN. The equation below will

provide optimum stability without RSL, provided that the above 2 conditions are met:

(24)

8.2.1.2.6 Power Diode Selection

Observation of the boost converter circuit shows that the average current through the diode is the average load

current, and the peak current through the diode is the peak current through the inductor. The diode should be

rated to handle more than its peak current. The peak diode current can be calculated using the formula:

ID(Peak) = IOUT/ (1−D) + ΔIL(25)

In the above equation, IOUT is the output current and ΔILhas been defined in Figure 32.

The peak reverse voltage for boost converter is equal to the regulator output voltage. The diode must be capable

of handling this voltage. To improve efficiency, a low forward drop schottky diode is recommended.

8.2.1.2.7 Power MOSFET Selection

The drive pin of LM3488 must be connected to the gate of an external MOSFET. In a boost topology, the drain of

the external N-Channel MOSFET is connected to the inductor and the source is connected to the ground. The

drive pin (DR) voltage depends on the input voltage (see the Typical Characteristics section). In most

applications, a logic level MOSFET can be used. For very low input voltages, a sub-logic level MOSFET should

be used.

The selected MOSFET directly controls the efficiency. The critical parameters for selection of a MOSFET are:

1. Minimum threshold voltage, VTH(MIN)

2. On-resistance, RDS(ON)

3. Total gate charge, Qg

4. Reverse transfer capacitance, CRSS

5. Maximum drain to source voltage, VDS(MAX)

The off-state voltage of the MOSFET is approximately equal to the output voltage. VDS(MAX) of the MOSFET must

be greater than the output voltage. The power losses in the MOSFET can be categorized into conduction losses

and ac switching or transition losses. RDS(ON) is needed to estimate the conduction losses. The conduction loss,

PCOND, is the I2R loss across the MOSFET. The maximum conduction loss is given by:

where

• DMAX is the maximum duty cycle. (26)

(27)

The turn-on and turn-off transitions of a MOSFET require times of tens of nano-seconds. CRSS and Qgare

needed to estimate the large instantaneous power loss that occurs during these transitions.

The amount of gate current required to turn the MOSFET on can be calculated using the formula:

VIN VIN

RIN

CIN

CBYPASS

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

IG= Qg.FS(28)

The required gate drive power to turn the MOSFET on is equal to the switching frequency times the energy

required to deliver the charge to bring the gate charge voltage to VDR (see the Electrical Characteristics table and

the Typical Characteristics section for the drive voltage specification).

PDrive = FS.Qg.VDR (29)

8.2.1.2.8 Input Capacitor Selection

Due to the presence of an inductor at the input of a boost converter, the input current waveform is continuous

and triangular, as shown in Figure 32. The inductor ensures that the input capacitor sees fairly low ripple

currents. However, as the input capacitor gets smaller, the input ripple goes up. The rms current in the input

capacitor is given by:

(30)

The input capacitor should be capable of handling the rms current. Although the input capacitor is not as critical

in a boost application, low values can cause impedance interactions. Therefore a good quality capacitor should

be chosen in the range of 10 µF to 20 µF. If a value lower than 10µF is used, then problems with impedance

interactions or switching noise can affect the LM3488. To improve performance, especially with VIN below 8 volts,

it is recommended to use a 20Ωresistor at the input to provide a RC filter. The resistor is placed in series with

the VIN pin with only a bypass capacitor attached to the VIN pin directly (see Figure 34). A 0.1-µF or 1-µF ceramic

capacitor is necessary in this configuration. The bulk input capacitor and inductor will connect on the other side

of the resistor with the input power supply.

Figure 34. Reducing IC Input Noise

8.2.1.2.9 Output Capacitor Selection

The output capacitor in a boost converter provides all the output current when the inductor is charging. As a

result it sees very large ripple currents. The output capacitor should be capable of handling the maximum rms

current. The rms current in the output capacitor is:

(31)

Where

(32)

and D, the duty cycle is equal to (VOUT −VIN)/VOUT.

The ESR and ESL of the output capacitor directly control the output ripple. Use capacitors with low ESR and ESL

at the output for high efficiency and low ripple voltage. Surface Mount tantalums, surface mount polymer

electrolytic and polymer tantalum, Sanyo- OSCON, or multi-layer ceramic capacitors are recommended at the

output.

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

8.2.1.3 Application Curve

Figure 35. Typical Startup Waveform (horizontal scale: 10ms/DIV)

8.2.2 Designing SEPIC Using LM3488

Since the LM3488 controls a low-side N-Channel MOSFET, it can also be used in SEPIC (Single Ended Primary

Inductance Converter) applications. An example of SEPIC using LM3488 is shown in Figure 36. As shown in

Figure 36, the output voltage can be higher or lower than the input voltage. The SEPIC uses two inductors to

step-up or step-down the input voltage. The inductors L1 and L2 can be two discrete inductors or two windings of

a coupled transformer since equal voltages are applied across the inductor throughout the switching cycle. Using

two discrete inductors allows use of catalog magnetics, as opposed to a custom transformer. The input ripple can

be reduced along with size by using the coupled windings of transformer for L1 and L2.

Figure 36. Typical SEPIC Converter

Due to the presence of the inductor L1 at the input, the SEPIC inherits all the benefits of a boost converter. One

main advantage of SEPIC over boost converter is the inherent input to output isolation. The capacitor CS isolates

the input from the output and provides protection against shorted or malfunctioning load. Hence, the A SEPIC is

useful for replacing boost circuits when true shutdown is required. This means that the output voltage falls to 0V

when the switch is turned off. In a boost converter, the output can only fall to the input voltage minus a diode

drop.

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

The duty cycle of a SEPIC is given by:

(33)

In the above equation, VQis the on-state voltage of the MOSFET, Q, and VDIODE is the forward voltage drop of

the diode.

8.2.2.1 Design Requirements

To calculate component values for a SEPIC converter, the power supply parameters shown in Table 3 should be

known. The design shown in Figure 36 is the result of starting with example values shown in Table 3

Table 3. SEPIC Design Parameters

DESIGN PARAMETER EXAMPLE VALUE

Input voltage range 3 V to 24 V

Output voltage 5 V

Maximum current 1 A

Operating frequency 350 kHz

Max peak to peak output ripple 200 mV

8.2.2.2 Detailed Design Procedure

8.2.2.2.1 Power MOSFET Selection

As in boost converter, the parameters governing the selection of the MOSFET are the minimum threshold

voltage, VTH(MIN), the on-resistance, RDS(ON), the total gate charge, Qg, the reverse transfer capacitance, CRSS,

and the maximum drain to source voltage, VDS(MAX). The peak switch voltage in a SEPIC is given by:

VSW(PEAK) = VIN + VOUT + VDIODE (34)

The selected MOSFET should satisfy the condition:

VDS(MAX) > VSW(PEAK) (35)

The peak switch current is given by:

(36)

The rms current through the switch is given by:

(37)

8.2.2.2.2 Power Diode Selection

The Power diode must be selected to handle the peak current and the peak reverse voltage. In a SEPIC, the

diode peak current is the same as the switch peak current. The off-state voltage or peak reverse voltage of the

diode is VIN + VOUT. Similar to the boost converter, the average diode current is equal to the output current.

Schottky diodes are recommended.

8.2.2.2.3 Selection Of Inductors L1 and L2

Proper selection of the inductors L1 and L2 to maintain constant current mode requires calculations of the

following parameters.

Average current in the inductors:

(38)

IL2AVE = IOUT (39)

RSEN = VSENSE - D(VSL + 'VSL)

ISWPEAK

'VOUT = IOUT

1-D +

'IL2

( ) ESR

L2 > (VIN - VQ)D

2IOUTfS

L1 > (VIN - VQ)(1-D)

2IOUTfS

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Peak to peak ripple current, to calculate core loss if necessary:

(40)

(41)

maintains the condition IL>ΔiL/2 to ensure constant current mode.

(42)

(43)

Peak current in the inductor, to ensure the inductor does not saturate:

(44)

(45)

IL1PK must be lower than the maximum current rating set by the current sense resistor.

The value of L1 can be increased above the minimum recommended to reduce input ripple and output ripple.

However, once DIL1 is less than 20% of IL1AVE, the benefit to output ripple is minimal.

By increasing the value of L2 above the minimum recommended, ΔIL2 can be reduced, which in turn will reduce

the output ripple voltage:

where

• ESR is the effective series resistance of the output capacitor. (46)

If L1 and L2 are wound on the same core, then L1 = L2 = L. All the equations above will hold true if the

inductance is replaced by 2L. A good choice for transformer with equal turns is Coiltronics CTX series Octopack.

8.2.2.2.4 Sense Resistor Selection

The peak current through the switch, ISW(PEAK) can be adjusted using the current sense resistor, RSEN, to provide

a certain output current. Resistor RSEN can be selected using the formula:

(47)

8.2.2.2.5 SEPIC Capacitor Selection

The selection of SEPIC capacitor, CS, depends on the rms current. The rms current of the SEPIC capacitor is

given by:

(48)

IRMS = ISWPK2 - ISWPK ('IL1 + 'IL2)+ ('IL1 + 'IL2)2

(1-D) - IOUT2

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

The SEPIC capacitor must be rated for a large ACrms current relative to the output power. This property makes

the SEPIC much better suited to lower power applications where the rms current through the capacitor is

relatively small (relative to capacitor technology). The voltage rating of the SEPIC capacitor must be greater than

the maximum input voltage. Tantalum capacitors are the best choice for SMT, having high rms current ratings

relative to size. Ceramic capacitors could be used, but the low C values will tend to cause larger changes in

voltage across the capacitor due to the large currents. High C value ceramics are expensive. Electrolytics work

well for through hole applications where the size required to meet the rms current rating can be accommodated.

There is an energy balance between CS and L1, which can be used to determine the value of the capacitor. The

basic energy balance equation is:

(49)

Where

(50)

is the ripple voltage across the SEPIC capacitor, and

(51)

is the ripple current through the inductor L1. The energy balance equation can be solved to provide a minimum

value for CS:

(52)

8.2.2.2.6 Input Capacitor Selection

Similar to a boost converter, the SEPIC has an inductor at the input. Hence, the input current waveform is

continuous and triangular. The inductor ensures that the input capacitor sees fairly low ripple currents. However,

as the input capacitor gets smaller, the input ripple goes up. The rms current in the input capacitor is given by:

(53)

The input capacitor should be capable of handling the rms current. Although the input capacitor is not as critical

in a boost application, low values can cause impedance interactions. Therefore a good quality capacitor should

be chosen in the range of 10µF to 20µF. If a value lower than 10µF is used, then problems with impedance

interactions or switching noise can affect the LM3488. To improve performance, especially with VIN below 8 volts,

it is recommended to use a 20Ωresistor at the input to provide a RC filter. The resistor is placed in series with

the VIN pin with only a bypass capacitor attached to the VIN pin directly (see Figure 34). A 0.1µF or 1µF ceramic

capacitor is necessary in this configuration. The bulk input capacitor and inductor will connect on the other side

of the resistor with the input power supply.

8.2.2.2.7 Output Capacitor Selection

The ESR and ESL of the output capacitor directly control the output ripple. Use low capacitors with low ESR and

ESL at the output for high efficiency and low ripple voltage. Surface mount tantalums, surface mount polymer

electrolytic and polymer tantalum, Sanyo- OSCON, or multi-layer ceramic capacitors are recommended at the

output.

The output capacitor of the SEPIC sees very large ripple currents (similar to the output capacitor of a boost

converter. The rms current through the output capacitor is given by:

(54)

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

The ESR and ESL of the output capacitor directly control the output ripple. Use low capacitors with low ESR and

ESL at the output for high efficiency and low ripple voltage. Surface mount tantalums, surface mount polymer

electrolytic and polymer tantalum, Sanyo- OSCON, or multi-layer ceramic capacitors are recommended at the

output for low ripple.

9 Power Supply Recommendations

The LM3488 is designed to operate from various DC power supply including a car battery. If so, VIN input should

be protected from reversal voltage and voltage dump over 48 Volts. The impedance of the input supply rail

should be low enough that the input current transient does not cause drop below VIN UVLO level. If the input

supply is connected by using long wires, additional bulk capacitance may be required in addition to normal input

capacitor.

10 Layout

10.1 Layout Guidelines

Good board layout is critical for switching controllers such as the LM3488. First the ground plane area must be

sufficient for thermal dissipation purposes and second, appropriate guidelines must be followed to reduce the

effects of switching noise. Switch mode converters are very fast switching devices. In such devices, the rapid

increase of input current combined with the parasitic trace inductance generates unwanted Ldi/dt noise spikes.

The magnitude of this noise tends to increase as the output current increases. This parasitic spike noise may

turn into electromagnetic interference (EMI), and can also cause problems in device performance. Therefore,

care must be taken in layout to minimize the effect of this switching noise. The current sensing circuit in current

mode devices can be easily effected by switching noise. This noise can cause duty cycle jitter which leads to

increased spectral noise. The most important layout rule is to keep the AC current loops as small as possible.

Figure 37 shows the current flow of a boost converter. The top schematic shows a dotted line which represents

the current flow during onstate and the middle schematic shows the current flow during off-state. The bottom

schematic shows the currents we refer to as AC currents. They are the most critical ones since current is

changing in very short time periods. The dotted lined traces of the bottom schematic are the once to make as

short as possible.

Figure 37. Current Flow in a Boost Application

Sense Resistor

Gate Resistor

Tune Performance

Output Diode

Power FET

Output Inductor

Set Frequency

Set Output

Voltage

Compensation

Chip Power Filter

Current

Sense Filter

To Input

Shutdown

To Output

AGND PGND

COMP

ISEN

To DR Pin

Output

Capacitors

Input

Capacitors

Current sense

trace changes

layers to allow

continuous

ground plane

LM3488

FA/SYNC/SD

VIN

LM3488

LM3488-Q1

www.ti.com

SNVS089O –JULY 2000–REVISED JULY 2015

Product Folder Links: LM3488 LM3488-Q1

Layout Guidelines (continued)

The PGND and AGND pins have to be connected to the same ground very close to the IC. To avoid ground loop

currents attach all the grounds of the system only at one point. A ceramic input capacitor should be connected as

close as possible to the Vin pin and grounded close to the GND pin. For a layout example please see AN-1204

LM378/LM3488 Evaluation Board (SNVA656A). For more information about layout in switch mode power

supplies please refer to AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054c).

10.2 Layout Example

Figure 38. Example Layout of a Boost Application using LM3488

11 Device and Documentation Support

11.1 Custom Design with WEBENCH Tools

Click here to create a custom design using the LM3488 device with the WEBENCH®Power Designer.

1. Start by entering your VIN, VOUT and IOUT requirements.

2. Optimize your design for key parameters like efficiency, footprint and cost using the optimizer dial and

compare this design with other possible solutions from Texas Instruments.

3. WEBENCH Power Designer provides you with a customized schematic along with a list of materials with real

time pricing and component availability.

4. In most cases, you will also be able to:

– Run electrical simulations to see important waveforms and circuit performance,

– Run thermal simulations to understand the thermal performance of your board,

– Export your customized schematic and layout into popular CAD formats,

– Print PDF reports for the design, and share your design with colleagues.

LM3488

LM3488-Q1

SNVS089O –JULY 2000–REVISED JULY 2015

www.ti.com

Product Folder Links: LM3488 LM3488-Q1

Custom Design with WEBENCH Tools (continued)

5. Get more information about WEBENCH tools at www.ti.com/webench.

11.2 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper

right corner, click on Alert me to register and receive a weekly digest of any product information that has

changed. For change details, review the revision history included in any revised document.

11.3 Related Links

The table below lists quick access links. Categories include technical documents, support and community

resources, tools and software, and quick access to sample or buy.

Table 4. Related Links

PARTS PRODUCT FOLDER SAMPLE & BUY TECHNICAL

DOCUMENTS TOOLS &

SOFTWARE SUPPORT &

COMMUNITY

LM3488 Click here Click here Click here Click here Click here

LM3488-Q1 Click here Click here Click here Click here Click here

11.4 Trademarks

WEBENCH is a registered trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

11.5 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

11.6 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

PACKAGE OPTION ADDENDUM

www.ti.com 11-Jan-2021

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM3488MM ACTIVE VSSOP DGK 8 1000 Non-RoHS

& Green Call TI Call TI S21B

LM3488MM/NOPB ACTIVE VSSOP DGK 8 1000 RoHS & Green NIPDAUAG | SN Level-1-260C-UNLIM -40 to 125 S21B

LM3488MMX/NOPB ACTIVE VSSOP DGK 8 3500 RoHS & Green NIPDAUAG | SN Level-1-260C-UNLIM -40 to 125 S21B

LM3488QMM/NOPB ACTIVE VSSOP DGK 8 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 SSKB

LM3488QMMX/NOPB ACTIVE VSSOP DGK 8 3500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 SSKB

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two

lines if the finish value exceeds the maximum column width.

PACKAGE OPTION ADDENDUM

www.ti.com 11-Jan-2021

Addendum-Page 2

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM3488MM VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

LM3488MM/NOPB VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

LM3488MMX/NOPB VSSOP DGK 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

LM3488QMM/NOPB VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

LM3488QMMX/NOPB VSSOP DGK 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 17-Jul-2020

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM3488MM VSSOP DGK 8 1000 210.0 185.0 35.0

LM3488MM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0

LM3488MMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0

LM3488QMM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0

LM3488QMMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 17-Jul-2020

Pack Materials-Page 2

IMPORTANT NOTICE AND DISCLAIMER

TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE

DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”

AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY

IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD

PARTY INTELLECTUAL PROPERTY RIGHTS.

These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate

TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable

standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you

permission to use these resources only for development of an application that uses the TI products described in the resource. Other

reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third party

intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims, damages,

costs, losses, and liabilities arising out of your use of these resources.

TI’s products are provided subject to TI’s Terms of Sale (https:www.ti.com/legal/termsofsale.html) or other applicable terms available either

on ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s

applicable warranties or warranty disclaimers for TI products.IMPORTANT NOTICE

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265