AIC1573CS datasheet(13/19 Pages) AIC

13 / 19 page

AIC1573

Each linear output initially follows a ramp. When

each output reaches sufficient voltage the input ref-

erence clamp slows the rate of output voltage rise.

The PGOOD signal toggles ‘high’ when all output

voltage levels have exceeded their under-voltage

levels.

Fault Protection

All four outputs are monitored and protected

against extreme overload. A sustained overload on

any output or over-voltage on PWM1 output dis-

ables all outputs and drive the FAULT/RT pin to

VCC.

0.15V

Over Current

Latch

4.0V

OC1

LUV

Fault

VCC

Fault Latch

POR

Counter

INHIBIT

OC2

Fig. 17 Simplified Schematic of Fault Logic

A simplified schematic is shown in figure 17. An

over-voltage detected on VSEN1 immediately sets

the fault latch. A sequence of three over-current

fault signals also sets the fault latch. The over-

current latch is set dependent on the status of the

over-current (OC1 and OC2), linear under-voltage

(LUV) and the soft-start signal. An under-voltage

event on either linear output (VSEN3, VSEN4) is

ignored until the soft-start interval. Cycling the bias

input voltage (+12V off then on) resets the counter

and the fault latch.

Gate Drive Overlap Protection

The Overlap Protection circuit ensures that the Bot-

tom MOSFET does not turn on until the Upper

MOSFET source has reached a voltage low enough

to ensure that shoot-through will not occur.

Over-Voltage Protection

During operation, a short on the upper PWM1

MOSFET (Q1) causes VOUT1 to increase. When

the output exceed the over-voltage threshold of

116% of DACOUT, the FAULT pin is set to fault

latch and turns Q2 on as required in order to regu-

late VOUT1 to 116% of DACOUT. The fault latch

raises the FAULT/RT pin close to VCC potential.

A separate over-voltage circuit provides protection

during the initial application of power. For voltage on

VCC pin below the power-on reset (and above ~4V),

Should VSEN1 exceed 1.0V, the lower MOSFET

(Q2) is driven on as needed to regulate VOUT1 to

1.0V.

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