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A8509GLBTR-T

Wide Input Voltage Range, High Efficiency 4-Channel Fault Tolerant LED Driver

Allegro MicroSystems 

A8509

Wide Input Voltage Range, High Efficiency

4-Channel Fault Tolerant LED Driver

Features and Benefits

• Four integrated high current sinks for LED strings; can be

tied together for even higher currents

• Fixed frequency current mode control with integrated gate

driver / boost controller; powerful gate driver to drive an

external N-channel MOSFET allows significant scaling

capability on the number of LEDs per string

• Parallel operation with one boost controller (master) and

up to three additional slave controllers; can run up to

16 strings of LEDs while populating only a single master

boost regulator

• Active current sharing between LED strings for

0.7% accuracy and 0.8% matching

• Wide input voltage range: 9 to 40 V

• Internal bias supply for single-supply operation (typically

VIN = 12 or 24 V)

• Separate Enable and PWM pins as interface for Enable

and PWM Dimming functions

• Fset / Sync function to either set the boost converter

switching frequency or synchronize at up to 800 kHz

• Protection Features

▫ Open or shorted LED pin protection

▫ Open Schottky protection

▫ Pulse-by-pulse current limit

▫ Overtemperature protection (OTP)

Packages

(Not to scale)

Description

The A8509 is a multi-output white LED driver for backlighting

LCD panels. It integrates a current-mode boost controller and

four individual current sinks.

The boost controller architecture allows for significant scaling

of boost voltage to optimize the solution for the required

number of LEDs per string. The FSET/SYNC pin either sets

the required boost switching frequency or synchronizes the

value in the range of 300 to 800 kHz.

The LED sink current value is set by an external ISET resistor

(see figure 1). The four LED sinks can also be combined to

achieve even higher current per LED string.

The A8509 provides protection against output shorts and

overvoltage, open or shorted LED pins, and overtemperature.

A dual-level, pulse-by-pulse current limit function provides

soft start and protects the external current switch against

high current overloads. As an option, the A8509 can drive an

external P-FET interfaced to the ¯F¯A¯¯U¯¯L¯¯T¯ pin to disconnect the

input supply from the system in the event of short-to-ground

in the boost converter.

Package options are 24-pin TSSOP (suffix LP) and SOICW

(LB) packages. The TSSOP has an exposed thermal pad, and

the SOICW has four interally-fused pins, for enhanced thermal

dissipation. The Both packages are lead (Pb) free, with 100%

matte tin leadframe plating.

24-pin TSSOP with

Exposed Thermal Pad

(LP package)

24-pin SOICW with

Four Internally-Fused Pins

(LB package)

30.00

25.00

20.00

15.00

10.00

5.00

60

RISET Value versus LED Current

100 140 180 220 260 300

ILED (mA)

Figure 1. Typical application circuit

showing 4 channels of LEDs; RZ-CZ

optional (component list shown in the

Typical Applications section)

Typical Application

VIN

L1

D1

VDD

CIN

COUT

Q1

R1

RSENSE

VIN

GATE SENP SENN

FAULT

CDR

CDD

RFSET

RISET

PWM

EN

VDR

VDD

FSET/SYNC

ISET

COMP

RZ

CZ CP

MODE

A8509

PAD

AGND PGND

VOUT

ROVP

OVP

LED1

LED2

LED3

LED4

A8509-DS

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