A8508 View Datasheet(PDF) - Allegro MicroSystems

Part Name

Description

MFG CO.

A8508

Wide Input Voltage Range, High Efficiency 8-Channel Fault Tolerant LED Driver

Allegro MicroSystems 

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A8508

Wide Input Voltage Range, High Efficiency

8-Channel Fault Tolerant LED Driver

The VDR circuit provides power to the gate driver of the A8508.

For best stability, use a decoupling capacitor in series with a

resistor between the VDR pin and GND. The recommended value

for the decoupling capacitor is 0.22 μF. The value of the series

resistor is typically between 5 and 10 Ω. If necessary, a larger

resistor value may be used to limit the rising slope of the gate

signal, in order to reduce EMI.

Shutdown

If the EN pin is pulled low, the IC will shut down immediately.

Fault protection during operation

The A8508 device constantly monitors the state of the system

to determine if any fault conditions occur during normal opera-

tion. The response to a triggered fault condition is summarized in

table 1. The possible fault conditions that the part can detect are:

• Open LED pin

• Shorted inductor with second level switch current protection

• VOUT short-to-ground

• ISET pin short-to-ground

• FSET pin short-to-ground

• Shorted LED

• Open Schottky diode

• Short Schottky diode protection with second level switch cur-

rent protection

• Thermal shutdown (TSD)

• Overvoltage protection (OVP)

1

C1

2

C2

VOUT

IIN

Soft start and

power-up

C4

LED detection

C3 period

FAULT

VGATE(PMOS)

t

Figure 31. Input disconnect switch power-up: (1) VOUT charges via 10 kΩ

resistor, (2) IIN current spike from charging COUT when the PMOS is

enabled; shows VOUT (ch1, 20 V/div.), IIN (ch2, 2 A/div.), ¯F¯¯A¯U¯¯L¯¯T¯ (ch3,

5 V/div.), and PMOS device VGATE (ch4, 5 V/div.), t = 2 ms/div.

Allegro MicroSystems, Inc.

17

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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