Wide Input Voltage Range, High Efficiency

Fault Tolerant LED Driver

A8521

2

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Absolute Maximum Ratings*

Characteristic

Symbol

Notes

Rating

Unit

LEDx Pins

–0.3 to 55

V

OVP Pin

–0.3 to 60

V

VIN, VSENSE, GATE Pins

by more than 0.4 V

–0.3 to 40

V

SW Pin

Continuous

–0.6 to 62

V

t < 50 ns

–1.0

V

¯F¯¯A¯¯¯U¯¯L¯¯T¯ Pin

-0.3 to 40

V

ISET, FSET, APWM, COMP Pins

–0.3 to 5.5

V

All Other Pins

–0.3 to 7

V

Operating Ambient Temperature

Range K

–40 to 125

ºC

Maximum Junction Temperature

150

ºC

Storage Temperature

–55 to 150

ºC

*Stresses beyond those listed in this table may cause permanent damage to the device. The Absolute Maximum ratings are

stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the Electrical

Characteristics table is not implied. Exposure to Absolute Maximum-rated conditions for extended periods may affect device reliability.

Selection Guide

Part Number

Packing*

A8521KLPTR-T

4000 pieces per 13-in. reel

Table of Contents

Specifications

2

Pin-out Diagram and Terminal List

3

Characteristic Performance

8

Functional Description

11

Enabling the IC

11

Powering up: LED pin short-to-ground check

11

Soft start function

13

Frequency selection

13

Sync

14

LED current setting and LED dimming

15

PWM dimming

15

APWM pin

16

Analog dimming

18

Description (continued)

The A8521 is provided in a 20-pin TSSOP package (suffix LP) with

an exposed pad for enhanced thermal dissipation. It is lead (Pb) free,

with 100% matte tin lead frame plating.

Overvoltage protection

19

Boost switch overcurrent protection

21

Input overcurrent protection and

disconnect switch

22

Setting the current sense resistor

23

Input UVLO

23

VDD

23

Shutdown

23

Fault protection during operation

24

Application Information

26

Design Example for Boost Configuration

26

Design Example for SEPIC Configuration

30

Package Outline Drawing

34