A8603KESTR-R datasheet(24/42 Pages) ALLEGRO

24 / 42 page

Multiple-Output Regulator for

Automotive LCD Displays

A8603

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

FAULT CONDITIONS

The A8603 has extensive fault detection mechanisms, to protect

against all perceivable faults at the IC level (pin open, pin short

to GND, pin short to neighboring pins, and so forth) and at the

system level (external component open/short, component value

changes from –50% to +100%, and so forth).

The FAULT pin of the A8603 has an open-drain pull-down device

internally. An external resistor is required to pull this pin to the

desired logic-high level (such as 5 V or 3.3 V) at no-fault. Choose

a resistor value such that, in case of fault, the current into the

FAULT pin is not more than 1 mA. For example, if the external

supply is 5 V, then the pull-up resistor should be 5 kΩ or higher.

In general, if a fault is detected, the A8603 halts operation and

pulls the FAULT pin low. It then attempts to restart operation

after a delay, tRESTART (programmable between 10 and 200 ms).

Internally there is a Fault counter that keeps track of how many

times any fault has occurred. If the Fault counter reaches maxi-

mum retry limit (programmable between 0 and 15), the A8603

stops any further attempts and returns to initial state with all

regulators disabled. The Fault status register can be read through

I2C commands, but internal enable signal is prohibited in this

state. The Fault counter is cleared only by a completed shutdown

sequence after EN = low, or by a power reset (VIN drops below

UVLO).

As an example: If the FSET pin is either open or shorted to GND,

the A8603 will report a fault by asserting FAULT = L once EN =

H. All output regulators are disabled in this case, but the user can

still use an I2C Read command to read the fault status registers,

and find out which type of fault has occurred. See “Diagnostic

Registers” section for details.

Over- and Undervoltage Protections

All regulator output pins (AVDD, VGL, VGH, VCOM) are

monitored for overvoltage and undervoltage faults during normal

operation.

In case of an output short, the output voltage may make a sudden

change that is either +20% over, or –20% under the target volt-

age. This will trigger the OVP/UVP fault and force the A8603

to shut down. The offending regulator is turned off immediately.

The other outputs are then shut down following normal sequence.

OVP/UVP detections are disabled during the startup sequence. If

any output fails to reach 90% of its target voltage within a time-

out period, tSS(TO) (50 ms typical), a fault is generated and then

the A8603 shuts down.

Each regulator output (AVDD, VGH, VGL and VCOM) is pro-

tected by its own independent overcurrent limit. When an output

current exceeds its limit, the corresponding regulator goes into

overcurrent protection mode to protect itself from damage. See

next section for illustrations of the protection characteristics.

If the overcurrent condition persists for 50 ms, all regulators are

turned off following the normal shutdown sequence. This is dif-

ferent from output OVP/UVP fault, where the offending regulator

is shut down immediately, while other regulators are shut down in

sequence.

Target

AVDD

33%

Output

Current

Output

Current

Output

Current

100%

VCOM

VGH, VGL

Target

3 V

Overcurrent Protection Mechanisms for AVDD, VCOM, VGH and VGL

Figure 12: Regulator Current Fold-Back in Case of Overcurrent Conditions

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