ALT80800KLPATR datasheet(13/23 Pages) ALLEGRO

13 / 23 page

Automotive-Grade, Constant-Current 2.0 A

PWM Dimmable Synchronous Buck LED Driver

ALT80800

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

Table 1: LED Open Fault Truth Table

FDSET

ADIM

FFnn

LED Open Fault Event?

PWM

FFnn+1

VCSREG < 25% × iLED Max Duty

High

No Open Fault

High

Yes, Open Fault

Low

Yes, Open Fault

Low

Yes, Open Fault

Low

No Open Fault

Low

No Open Fault

FDSET High means FDSET > REF1; FDSET Low means FDSET < REF1;

ADIM High means ADIM > 264 mV; ADIM Low means ADIM < 264 mV

When output Short fault (such as LED shorted to ground or out-

put capacitor shorted to ground) occurs, FFn will be flagged as

VOUT drops below 1.5 V and ADIM voltage is above 264 mV; but

regulator will not enter into Hiccup mode and will work continu-

ously. When short is removed, ALT80800 will return to normal

operation.

When an LED Open/Short fault occurs, the Fault pin will be

flagged if the fault remains active after a deglitch period (tFDG).

A mask timer (tMASK) is also introduced whenever PWM signal

goes from Low to High. During this mask time, faults will not be

detected, so the fault will not be detected when the PWM pulse

width is less than this mask time. When PWM goes low, fault

flag is latched. Fault flag will keep prior state when PWM is

Low.

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