A8503GECTR-T View Datasheet(PDF) - Allegro MicroSystems

Part Name

Description

MFG CO.

A8503GECTR-T

High Efficiency 6-Channel, 2 MHz, WLED/RGB Driver for Medium Displays, with Integrated 55 V Power Switch

Allegro MicroSystems 

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A8503

High Efficiency 6-Channel, 2 MHz, WLED/RGB Driver for

Medium Displays, with Integrated 55 V Power Switch

Functional Description

The A8503 is a multi-output WLED/RGB LED driver for

backlighting medium-size displays. It has an integrated boost

converter to increase input supply voltage, allowing it to drive up

to 12 LEDs per channel on 6 channels with a Vf (max) of 3.2 V

at 20 mA per LED, at 5 V supply. The boost converter is a fixed

frequency current-mode converter. The switching frequency can

be set in a range from 600 kHz to 2 MHz, by an external resis-

tor, RFSET , connected between FSET and ground. The integrated

boost DMOS switch is rated for 55 V, 2 A. This switch is pro-

tected against overvoltage, and has pulse-by-pulse current limit-

ing. The current limiting is independent of duty cycle.

The A8503 has six well-matched current sinks that provide

regulated current through the LEDs, for uniform display bright-

ness. The boost converter is controlled by monitoring all LEDx

pins simultaneously and continuously. All LED sinks are rated for

34 V to allow PWM dimming control.

LED Current Setting

The maximum LED current can be set, to 32 mA/channel,

through the ISET pin. Connect a resistor, RISET, between this pin

and ground to set the reference current level, ISET. The value of

ISET (mA) is determined by:

ISET = 1.235 / RISET (kΩ) .

The resulting current is multiplied internally by a gain of 320,

then is mirrored to all enabled LEDx pins. This sets the maximum

current through LEDx, referred as the 100% Current, as shown

in figure 2A. The LEDx current can be reduced from the 100%

Current value by applying an external PWM signal on the PWM

pin (see figure 2B).

Boost Switching Frequency Setting

Connect an external resistor between the FSET pin and AGND,

to set boost switching frequency, fSW . The value of the boost

switching frequency, fSW (MHz), is determined by:

fSW = 52 / RFSET (kΩ) .

The typical RFSET versus frequency curve is shown in figure 3.

Enable

The IC turns on when a high signal is applied on the EN pin and

turns off when this pin is pulled low.

PWM Dimming

The A8503 has a very wide range of PWM signal input. It can

accept a PWM signal from 100 Hz to 5 kHz. When a PWM high

signal is applied, the LEDx pins sink 100% Current. When the

34

32

30

28

26

24

22

20

18

16

14

12

10

12 14 16 18 20 22 24 26 28 30 32 34 36 38

RISET (kΩ)

(A)

325

323

321

VIN (V)

319

4.5

5.0

317

5.5

315

12 14 16 18 20 22 24 26 28 30 32 34 36 38

RISET (kΩ)

(B)

Figure 2. Effect of value of RISET on current through an LED string. Panel

A shows level of 100% current, and panel B shows LEDx gain.

2

1.8

1.6

1.4

VIN (V)

1.2

4.5

1

5.0

5.5

0.8

0.6

25 30 35 40 45 50 55 60 65 70 75 80 85

RFSET (kΩ)

Figure 3. Switching frequency setting versus RFSET (VIN = 5 V,

VBAT = 12 V).

Allegro MicroSystems, Inc.

11

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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