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LM3432SQX/NOPB

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May 22, 2008

LM3432/LM3432B

6-Channel Current Regulator for LED Backlight Application

General Description

Features

The LM3432/LM3432B are 6-channel high voltage current

regulators which provide a simple solution for LED backlight

applications. These devices incorporate six individual current

regulator channels to give accurate driving current for each

LED string. The string-to-string tolerance is kept within ±2.0%.

Additionally, the Dynamic Headroom Control output can com-

municate with a LM3430 boost regulator to adjust the LED

supply voltage to the lowest level needed to keep the string

current in regulation, yielding optimal overall system efficien-

cy.

Dynamic Headroom Control (DHC) output to maximize

■

efficiency when used in conjunction with National

Semiconductor's LM3430 Boost Controller for LED

Backlighting

Current sinking adjustable up to 40mA in each string

■

Fast current switching slew rate, t_r= 60ns typical

Wide dimming ratio, up to 4000:1 with f_DIM= 500Hz

High LED driving voltage up to 80V

±2.0% current matching between strings

The 6-channel current sink can be adjusted from 15mA to

40mA by an external resistor. Their output drivers can with-

stand up to 80V. Digital PWM or analog voltage signal can be

used to control the duty cycle of all the channels. With a fast

current switching slew rate, t_r= 60ns typical, accurate current

control and wide dimming ratio during PWM dimming are en-

sured.

Accepts both Digital and Analog dimming control

LED open/short fault indication (For LM3432B, no open

fault indication)

Over-Temperature Indication

■

Internal Thermal Shutdown with Hysteresis

Low profile, thermally enhanced LLP-24 (5x4x0.8mm) and

eTSSOP-28 (9.7x6.4x1.1mm) packages (The LM3432B is

available in the LLP-24 only)

The LM3432/LM3432B contain LED open/short circuit and

over-temperature fault signaling to the system micro-con-

troller (the LM3432B does not include open circuit fault sig-

naling). These devices are available in a low profile, thermally

enhanced 24 lead LLP package. The LM3432 is also avail-

able in the 28 lead eTSSOP.

Applications

LCD display backlight applications

■

General lighting solutions

300064

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Typical Application Circuit

30006401

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Connection Diagrams

30006431

Top View

28 Lead Plastic eTSSOP-28

NS Package Number MXA28A

30006402

Top View

24 Lead Plastic LLP-24

NS Package Number SQA24B

Ordering Information

Part Number

For LM3432

Package Type

NS Package Drawing

Supplied As

LM3432SQ

LM3432SQX

LM3432SQE

LM3432MH

LM3432MHX

1000 Units on Tape and Reel

4500 Units on Tape and Reel

250 Units on Tape and Reel

Rail of 48 Units

LLP-24

SQA24B

MXA28A

eTSSOP-28

2500 Units on Tape and Reel

For LM3432B

LM3432BSQ

LM3432BSQX

LM3432BSQE

1000 Units on Tape and Reel

4500 Units on Tape and Reel

250 Units on Tape and Reel

LLP-24

SQA24B

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Pin Descriptions

Pin Number

Name

Description

LLP-24

eTSSOP-28

VCC

IREF

Internal linear regulator output, needs 680nF minimum

for stability.

I_OUTcurrent setting pin. An external resistor is used to

program the string current.

AGND

CDHC

Analog ground

An external capacitor to ground programs the Dynamic

Headroom Control (DHC) response time constant.

VDHC

DHC voltage output. Connecting this output through a

gain setting resistor to the DHC pin of National

Semiconductor's LM3430 enables the DHC function.

Device Enable, active HIGH.

MODE

Dimming mode select pin. Short to ground for Digital

PWM dimming or connect to an external capacitor to

ground for analog dimming.

DIM

Digital PWM or Analog voltage input for IOUT duty cycle.

Open drain active LOW output for output fault.

FAULTb

OTMb

Open drain active LOW over temperature warning

output.

12,13,15,17,19,20 15, 17, 19, 21, 23, 25

IOUT1-6

Constant current sink outputs, adjustable 15mA to

40mA, voltage across this pin can be up to 80V max.

27, 28

PGND

VIN

Power Ground.

Supply voltage input, from 6V to 40V.

No connection and should be left open.

11,14,16,18,21,23 2, 3, 4, 16, 18, 20, 22,

24, 26

Thermal connection pad, connect directly to GND.

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ꢀ

Absolute Maximum Ratings (Notes 1, 6)

ESD Susceptibility (Note 2)

Human Body Model

Lead Temperature

Vapor Phase (60 sec.)

Infra-red (15 sec.)

Maximum Junction Temp.

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

2.0kV

215°C

220°C

150°C

VIN Voltage

-0.3V to 42V

-0.3V to 7V

-0.3V to 82V

-0.3V to 7V

ꢀ

IREF Voltage

IOUT1 through IOUT6 Voltage

VCC Voltage

EN Voltage

FAULTb, OTMb Voltage

MODE Voltage

PWM Voltage

VDHC Voltage

CDHC Voltage

ꢀ

Operating Ranges (Note 1)

Supply Voltage, VIN

IOUT1 through IOUT6 Voltage

Operating Junction Temp.

Storage Temperature

Thermal Resistance, θ_JA(Note 3)

LLP-24

6 to 40V

0 to 80V

-40°C to +125°C

-65°C to +150°C

33.2°C/W

29°C/W

eTSSOP-28

ꢀ

Electrical Characteristics Limits in standard type are for T_J= 25°C only; limits in boldface type apply over the

junction temperature (T_J) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical

correlation. V_IN= 18V, R_IREF= 54.7 kΩ, V_EN= 5V, V_MODE= 0V, V_DIM= 5V and V_OUT1-6= 1.2V unless otherwise indicated (Note

4). Parameter limits apply to both the LM3432 and LM3432B unless otherwise indicated.

Symbol

Input Characteristics

I_SHDNShutdown Input Supply Current

I_Q

Parameter

Conditions

Min

Typ

Max Units

EN = 0V, DIM = 0V

µA

Quiescent Current from VIN

Enable Threshold Voltage

Enable Threshold Hysteresis

Enable pin Pull-up Current

2.25 2.65

V_EN

V_ENrising

1.48 1.75

V_{EN_HYST}

I_EN

0.4

0.5

EN = 0V

EN = 2V

µA

VCC Regulator

V_CCreg

V_{CCreg_1}

V_{CCreg_2}

I_{VCC_SC}

V_CCUVLO

VCC Regulated Output

4.7

5.25

VCC Regulated Output at Max. VIN

VCC Regulated Output at Min. VIN

VCC Short-Circuit Current

V_IN= 40V

V_IN= 6V, I_VCC= 2mA

V_IN= 6V, VCC = 0V

VCC rising

4.8

VCC UVLO Upper Threshold

3.9

4.15

0.375

4.4

V_{CCUVLO_HYST}VCC UVLO Hysteresis

Analog PWM control

I_MODE

MODE pin Output Current

MODE pin Peak Voltage

MODE pin Valley Voltage

MODE = 2V

3.1

1.0

µA

V_{MODE_PK}

V_{MODE_VA}

C_MODE= 5.6nF

Digital PWM control

V_{PWM_HIGH}PWM Voltage HIGH

V_{PWM_LOW}PWM Voltage LOW

Dynamic Headroom Control Output

MODE = GND

1.7

V_{DHC_MAX}

VDHC pin Max. Output Voltage

I_VDHC= 2mA

2.5

I_{VDHC_MAX}VDHC pin Max. Output Current

V_{DHC_REG_20}VDHC Regulation at 20mA

V_{DHC_REG_40}VDHC Regulation at 40mA

V_DHC= 1.2V

R_IREF= 54.7k, C_DHC= 100nF

R_IREF= 27.5k, C_DHC= 100nF

0.625

1.25

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Symbol

Switching Characteristics

t_{pd_H}IOUT Rising Edge Phase Delay

T_rIOUT Rise Time

Parameter

Conditions

Min

Typ

Max Units

MODE = GND, Pulsing PWM 10µs

500

MODE = GND, rising edge from 10%

to 90% of IOUT

Output Current

V_IREF

IREF pin Voltage

1.215 1.245 1.27

6V ≤ V_IN≤ 40V

I_OUT20

Constant Current Sink of 20mA

R_IREF= 54.7k, V_IOUT1-6= 1.1V

18.85

21.05

18.5

21.4

I_OUT40

Constant Current Sink of 40mA

R_IREF= 27.5k, V_IOUT1-6= 1.6V

37.9

41.55

37.3

42.15

I_{OUT20_match}Output Current Matching of I_OUT20(Note 5)

I_{OUT40_match}Output Current Matching of I_OUT40(Note 5)

2.25

6V ≤ V_IN≤ 40V

I_{OUT_max}

Maximum Output Current, IREF shorted to

GND.

V_IREF= 0V, V_IOUT= 4.5V

110

V_{DROP_IOUT20}Dropout Voltage of I_OUT20(Note 7)

V_{DROP_IOUT40}Dropout Voltage of I_OUT40(Note 7)

R_IREF= 54.7k

0.3 0.525

0.6 1.125

R_IREF= 27.5k

I_{OUT_OFF}

Output Current when EN is LOW

EN = 0, V_OUT= 80V

0.025

µA

Fault Detection

V_SHORTFAULTV_IOUTShort Fault Threshold

FAULTb goes LOW during V_IOUT

rising, other V_IOUT_s= 1.0V

7.3

7.9

8.8

t_{D_SHORTFAULT}Short Fault Delay

V_IOUTset to 10V, FAULTb goes LOW,

other V_IOUT_s= 1.0V

150

µs

t_{D_OPENFAULT}Open Fault Delay (LM3432 only)

V_{FAULT_LOW}FAULTb and OTMb LOW

I_{LEAK_FAULT}FAULTb and OTMb Open Leakage

Thermal Protection

V_IOUTXset open, FAULTb goes LOW

5mA into FAULTb

µs

0.7

V_FAULTb= V_OTMb= 5V

0.005

µA

OTM

OTM_HYST

T_SD

Over Temperature Monitor Threshold

Over Temperature Monitor Hysteresis

Thermal Shutdown Threshold

125

°C

165

T_SDHYST

Thermal Shutdown Hysteresis

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. The Recommended Operating Limits define the conditions within

which the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.

Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, T_{J_MAX}, the junction-to-ambient thermal resistance, θ_JA

and the ambient temperature, T_A. The maximum allowable power dissipation at any ambient temperature is calculated using: P_{D_MAX}= (T_{J_MAX}- T_A)/θ_JA. Exceeding

the maximum allowable power dissipation will cause excessive die temperature.

Note 4: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%

tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate

Average Outgoing Quality Level (AOQL). Typical values represent the most likely parametric norm at T_J= 25°C and are provided for reference purposes only.

Note 5: I_{OUT_match}is the greatest percentage delta between output string currents with respect to the median.

Note 6: Rating limits apply to both the LM3432 and LM3432B.

Note 7: Dropout voltage is defined as the IOUT pin to GND voltage at which the output current sink drops 10% from the nominal value.

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Typical Performance Characteristics Unless otherwise specified, the following conditions apply: V_IN

18V, R_IREF= 54.7 kΩ, V_EN= 5V, V_MODE= 0V, V_DIM= 5V and V_OUT1-6= 1.2V. Typical performance characteristics are valid for both

the LM3432 and LM3432B unless otherwise indicated.

Quiescent Current vs Supply Voltage

Shutdown Current vs Supply Voltage

30006403

30006404

VCC Regulator Output vs Supply Voltage

Current Setting Reference Voltage vs Supply Voltage

30006405

30006406

Average String Current vs Current Setting Resistance

Output Current Matching vs Temperature

30006408

30006407

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PWM Dimming Frequency vs C_MODE

PWM Digital Dimming Operation

(Channel 1 Waveform)

30006410

30006409

PWM Dimming Characteristic, Rising Edge

(Channel 1 Waveform)

PWM Dimming Characteristic, Falling Edge

(Channel 1 Waveform)

30006411

30006412

Analog Dimming Operation

30006413

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Simplified Functional Block Diagram

30006415

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ANALOG DIMMING OF LED STRINGS

Functional Description

Dimming of LED brightness is achieved by Pulse Width Mod-

ulation (PWM) control of the string currents. The LM3432/

LM3432B accepts both analog voltage and PWM digital dim-

OVERVIEW

The LM3432/LM3432B are 6-channel high voltage current

regulators for LED backlight applications which incorporates

individual channel current regulators to give accurate current

sinking for each LED string. String to string tolerance is kept

within ±2.0% at 40 mA and ±2.25% at 20 mA. The 6-channels

current sinks can be adjusted from 15 mA to 40 mA by an

external resistor. Channel outputs can withstand up to 80V.

Channel 5 or 6 output can be disabled by shorting the selected

output pin to ground prior to power-up. Both the digital PWM

dimming signal and analog voltage signal can be used to

control the duty cycle of all the six channels. The LM3432/

LM3432B also provide fault indications to the system MCU for

an LED open (included in the LM3432 only) or short circuit or

an over-temperature condition.

ming input signals for this feature. With a capacitor (C_MODE

)

connected across the MODE pin and ground, the device will

monitor the voltage level at the DIM pin and generate the re-

quired PWM control signal internally. The internal implemen-

tation of the LM3432/LM3432B’s dimming function is illustrat-

ed in Figure 1.

INTERNAL 5V LINEAR REGULATOR

An internal 5V linear regulator with an Under-Voltage Lock-

Out (UVLO) function is integrated within the LM3432/

LM3432B. This regulated 5V is used for internal circuitry and

can support a small amount of external loading, not to exceed

2 mA when V_IN= 6V. The supply input pin (VIN) can be con-

nected directly to an input voltage up to 40V, with transient

capability up to 42V. The VCC output regulates at 5V and is

current limited to 9 mA. To ensure stable operation, the ex-

ternal capacitor C_VCCmust be at least 680 nF with 1 µF

recommended. If the voltage at the VCC pin drops below the

UVLO threshold of 3.8V, the device will shut down the output

channels and other functional blocks. Normal operation will

be resumed once the V_CCvoltage is allowed to rise above the

UVLO rising threshold of 4.15V.

30006417

FIGURE 1. Analog Dimming of LEDs

An internal current source of 34 µA (typical) will charge the

external capacitor (C_MODE) linearly until it reaches 3V. The

comparator (Comp1) then forces C_MODEto be discharged to

1V very quickly. By repeating the cycle, a saw-tooth waveform

as shown in Figure 1 is generated. Comparator (Comp2)

compares this ramp waveform with the external dc voltage at

the DIM pin generating the desired PWM control signal.

BANDGAP VOLTAGE REFERENCE

A precision reference voltage is required for accurate control

of the output currents. The LM3432/LM3432B contain a

bandgap voltage reference block that provides a high preci-

sion reference voltage for internal operation. The bandgap

reference voltage is typically trimmed to 1.245V.

When V_DIM≤ 1V, ON duty factor, D_ON= 0% and when V_DIM

≥ 3V, D_ON= 100%. The frequency of the PWM control signal

can be calculated as shown below.

OUTPUT CURRENT REGULATOR (IOUT1 to IOUT6)

The LM3432/LM3432B contains six individual integrated cur-

rent regulators to give accurate current sinking for each LED

string. String to string tolerance is kept within ±2.0% at 40 mA

and ±2.25% at 20 mA. The sink current level is adjusted by

an external resistor, R_IREFin the range of 15 mA to 40 mA.

The IOUT pins can withstand up to 80V. The ability to with-

stand high voltage enables the user to add more LEDs in a

single string. The calculation of I_OUTwith respect to R_IREFis

shown below.

PWM DIGITAL DIMMING of LED STRINGS

Alternatively, the dimming control can be implemented by di-

rect application of a digital signal to the device. With the

MODE pin connected to ground, an externally applied PWM

dimming signal is applied to the DIM pin. The peak amplitude

of the externally applied PWM signal should be greater than

1.5V to guarantee clean PWM switching.

Channels 5 and 6 are designed to be user disabled without

activating the fault detection circuitry. With this feature, the

user can readily configure the device to a 4, 5 or 6 channel

driver. In order to disable a channel, the IOUT5 and/or IOUT6

pin(s) must be tied to ground before powering up the device.

During power-up, channels 5 and 6 will be checked and any

grounded channel(s) will be automatically disabled. The dis-

abled status will remain until either power is recycled or the

enable (EN) pin is toggled.

During PWM dimming, channels are not switched simultane-

ously in an effort to minimize large surge currents from being

drawn from the LED supply rail. Each channel will have 0.5

µs phase delay with respect to the preceding channel. As a

consequence of the phase delay, for a control pulse width less

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than 0.5 µs, the duty cycle will be rounded down to 0% and

for a control pulse width less than 0.5 µs off time, the duty

cycle will be rounded up to 100%. Therefore, 0.5µs becomes

the finest pulse width resolution that can be realized. The

PWM switching timing for all six channels is shown in Figure

30006420

FIGURE 2. PWM Dimming Switching Timing

LED SHORT FAULT DETECT

With DHC

detect feature will be active for all channels. In the event an

LED short fault condition occurs and causes the voltage be-

tween any of the IOUT pin and ground to exceed the typical

short fault threshold of 7.9V for more than 150 μs, the affected

channel(s) will be latched off and the FAULTb pin will be

pulled to ground. The affected channel(s) will remain latched

off until recycling power or toggling the EN pin. All of the other

channels that are not affected will continue to function nor-

mally. If the voltages between all IOUT pins and ground are

greater than 2V typical, the Short Fault Detect feature will be

disabled to prevent false triggering of the short fault detect

function.

If the Dynamic Headroom Control (DHC) feature is used, the

lowest voltage between the IOUT pins and ground among the

strings will be regulated to 0.625V typical (I_LED= 20 mA) by

lowering the LED supply rail voltage, V_LED. If an LED short

fault condition occurs and causes the voltage between any of

the IOUT pins and ground to exceed the typical short fault

threshold of 7.9V for more than 150 µs, the affected channel

(s) will be latched off and the FAULTb pin will be pulled to

ground. The affected channel(s) will remain latched off until

recycling power or toggling the EN pin. All of the other chan-

nels that are not affected will continue to function normally.

LED OPEN FAULT DETECT (LM3432 ONLY)

For the LM3432, if an open fault should occur and the affected

channel sinks no current for greater than 50 µs, it will be

latched off (until recycling power or toggling EN pin). The

FAULTb pin’s output will be pulled to ground while the other

channels keep functioning normally. The open fault detection

and FAULTb indication features are inactive in the LM3432B.

Without DHC

In applications where the DHC function is not used, the IOUT

pin voltage on each string will be the voltage difference be-

tween the LED supply rail voltage, V_LED, and the voltage drop

across the entire LED string. If the voltage between any of the

IOUT pins and ground is less than 2V typical, the short fault

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30006429

FIGURE 3. Fault Detect Functional Block Diagram

OVER-TEMPERATURE MONITOR

DYNAMIC HEADROOM CONTROL

If the LM3432/LM3432B junction temperature exceeds ap-

proximately 125°C, the OTMb pin will be pulled to ground but

the part will continue to function. Action must be taken to lower

the temperature at this point. The PWM duty factor may be

lowered as an example to reduce the amount of heat gener-

ated, which will in turn lower the die temperature. If the

junction temperature is allowed to rise beyond approximately

165°C, the part will shut down. When the device is cooled

down to about 145°C, device operation will resume.

To use the DHC function, connect a gain setting resistor from

the VDHC pin of the LM3432/LM3432B to the VDHC pin of

the LM3430 (National Semiconductor’s Boost Controller for

LED Backlighting) that is supplying power to the LED rails.

The LM3432/LM3432B’s DHC function will regulate the volt-

age between the IOUT pins and ground to a minimum of

0.625V typical (IOUT = 20 mA) to optimize overall efficiency.

A large DHC time constant needs to be set in order not to

interfere with the loop response of the DC-DC converter. This

can be implemented by connecting a capacitor from the

LM3432/LM3432B’s CDHC pin to ground. If the DHC function

is not needed, leave the VDHC pin floating. When operated

in this manner, if the lowest voltage between any of the IOUT

pins and ground is greater than 2V, the LED short fault de-

tection function will be disabled. For the LM3432B, if any open

condition occurs on any channels, the DHC function will be

inactive and the LED supply rail voltage from the LM3430 will

stay at its preset level. If the excess headroom voltage is

greater than the short fault detect threshold, 7.3V(min), the

device may latch off the LED string(s) due to short fault pro-

tection. In order to insure the proper operation of good LED

strings, designers must design for sufficient excess head-

room voltage below the short fault detect threshold.

Note that this thermal shutdown protection is only intended as

a fault mode protection feature. Device operation above rated

maximum operating junction temperature is neither recom-

mended nor guaranteed.

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an LED panel of up to about 120 white LEDs can be illumi-

nated. A typical application configuration driving six strings

with twelve white LEDs per string is shown in Figure 4.

Applications Information

The LM3432/LM3432B provide a simple and handy solution

for LED driving. With only a few external passive components,

30006421

FIGURE 4. Typical Application Schematic to Drive 72 White LEDs (@20 mA) (PWM Digital Dimming)

DETERMINATION OF EXTERNAL COMPONENTS

For the example shown in Figure 4, the string current is 20

mA. Applying to the equation:

The typical application only requires three external compo-

nents. The selection of those components is described in

detail below.

Programming of String Current, IOUT1 to IOUT6

The string current can be programmed by an external resistor,

R_IREF. The equation to calculate the resistance of this resistor

is shown below.

Selecting the VCC Output Capacitor, C_VCC

For proper operation, a VCC output capacitor (C_VCC) of at

least 680 nF is required for stability reason. The recommend-

ed C_VCCcapacitance is 1 µF.

In order to ensure good current regulation over the full oper-

ating temperature range, a high quality resistor with ±1%

tolerance and a low temperature coefficient is recommended.

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Selecting the VIN Capacitor, C_VIN

Driving High Current LEDs

The purpose of this capacitor is to supply transient current to

the device and suppress VIN noise in order to ensure proper

operation. A low ESR ceramic capacitor with good high fre-

quency performance is recommended. The capacitance can

range from 0.1 µF to 1 µF.

The LM3432/LM3432B can support string currents from 15

mA to 40 mA. If the application needs to drive high current

LEDs that require more than 40 mA per string, the LM3432/

LM3432B provides the alternative of connecting several IOUT

ports together to achieve higher output current per string. With

this approach, there is the obvious trade off between higher

output current and number of strings driven. Two possible

configurations are illustrated in Figure 5.

Analog Dimming Control

If analog dimming control is required, a capacitor, C_MODE

should be connected from the MODE pin to ground instead of

shorting the MODE pin to ground. The relationship between

the PWM dimming frequency and the capacitance of C_MODE

is illustrated below.

When V_PWM≤ 1V, D_ON= 0% and when V_PWM≥ 3V, D_ON

100%

The LED dimming ratio is calculated from the ratio of minimum

ON duty factor to the maximum ON duty factor. With the

LM3432/LM3432B, the LEDs can be fully turned on up to

100% ON duty factor and the minimum ON duty factor is lim-

ited by the phase delay time, 0.5 µs. The dimming ratio can

be estimated as below.

As an example, if the PWM dimming frequency is set to 500

Hz, the best achievable dimming ratio is:

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30006427

FIGURE 5. Achieving Higher LED String Current by Grouping IOUT Ports

Dynamic Headroom Control, DHC with LM3430

must be set to a large enough value by adding a capacitor

from CDHC pin to ground.

When the LM3432/LM3432B are powered with National

Semiconductor's Boost Controller for LED Backlighting,

LM3430, the Dynamic Headroom Control (DHC) feature

helps to provide the optimal system efficiency. By connecting

VDHC through a gain setting resistor to the DHC pin of the

LM3430 that is supplying the LED power rail, the LM3432/

LM3432B’s DHC function will regulate the minimum of the ON

voltage of the six channels to 0.625V typical (I_OUT= 20 mA).

This is the minimum voltage headroom required at outputs to

keep the current regulator in its linear operating range. In or-

der not to interfere with the feedback loop response of the

upstream DC-DC converter, the DHC response time constant

Figure 6 is an application schematic of a LED panel driver

using both the LM3430 and the LM3432/LM3432B with the

Dynamic Headroom Control function enabled. The LM3430

boosts a voltage from VIN to 50V nominal to supply the LED

strings. With the DHC function disabled, the LM3430 will keep

the LED string supply regulated at 50V. When the DHC is

enabled, this voltage will dynamically be regulated down to a

voltage that can just keep all LED string currents in regulation.

That is about 40V in the application shown in Figure 6. The

reduction in this rail voltage can significantly improve the

overall system efficiency.

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30006428

FIGURE 6. LM3430 + LM3432/LM3432B Application Schematic with Dynamic Headroom Control Enabled

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Physical Dimensions inches (millimeters) unless otherwise noted

24-Lead LLP Package

NS Package Number SQA24B

28-Lead eTSSOP Package

NS Package Number MXA28A

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Notes

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