Multiple-Output Regulator for

Automotive LCD Displays

A8603

25

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

AB

C

DE

FAULT

VGH

VGL

VCOM

AVDD

Internal

Enable

Target

0 V

Target

0 V

0 V

Target

0 V

0 V

30%

Watchdog Timer (50 ms)

t

SU_TO

Shutdown

Cool Down Timer (10-200 ms)

t

RESTART

Sequence of events:

B: During startup, VGL is unable to reach its regulation target due to an output short or unexpected heavy load.

C: After Watchdog Timer expired, the A8603 reports that a fault has occurred (by asserting FALUT = L) and begins to shutdown all its output

regulators in normal sequence. Fault counter is incremented by 1.

D: When the last regulator (VGH in this case) has finished shutdown, the A8603 waits for a cooldown period (programmable between 10 and

200 ms).

E: Retry startup as long as the maximum number or retries (programmable between 0 and 15) is not exceeded.

Figure 13: Timing Diagram where VGL Failed to Reach Its Target Voltage at Startup

Examples of Various Fault Conditions

Overcurrent Protection

Each output regulator has a built-in current limit to prevent dam-

ages from overcurrent. During startup, a regulator may initially

operate in overcurrent protection mode while its output capaci-

tor is being charged. Normally, the current will reduce once the

output voltage has reached target value. In case there is an output

short, or if the output capacitor is much larger than expected, the

OCP mode may last for 50 ms. At this point, an OCP fault is gen-

erated. The IC then begins to shut down all regulators according

to programmed shutdown sequence.