SC1544 datasheet(14/15 Pages) SEMTECH

14 / 15 page

 2002 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC1544

PRELIMINARY

.ault Protection Hints (Cont.)

that the OCP times out then the outputs will latch off.

Then if the AC power returns after the OCP latches off,

but before the 5VSB supply drops below UVLO, then the

device will not start up again until EN or 5VSB is cycled.

One way to avoid this happening is to force the device

into S3 if PWR_OK goes low but S3 and S5 remain high

using the circuit shown below. This will supply the

outputs from 5VSB which will either cause 5VSB to drop

below UVLO and reset the part when the AC power comes

back up, or it may prevent OCP occuring at all. Either way

correct functionality will be guaranteed once AC power

returns.

1N4148

PWR_OK

/SLP_S3

SC1544-2.5

2.5VDM

AGP

TYPEDET

PWR_OK

/S3

/S5

USB

PCI

-CAP

+CAP

5VSB

5VD

G2/3

GND

3.3VD

1.8V

4.7k

Incorrect Signals .rom Silver Box: Some silver boxes

have been found that produce incorrect voltages on the

PWR_OK line, producing dangerous negative voltage

spikes up to -1V or greater. Such spikes exceed the

absolute maximum ratings for this device and can cause

the device to malfunction. If a supply produces such

spikes they can be clamped to GND using a small schottky

diode as shown below, completely removing any threat.

PWR_OK

U 1

SC1544-2.5

2.5VDM

AGP

TYPEDET

PWR_OK

/S3

/S5

USB

PCI

-CAP

+CAP

5VSB

5VD

G2/3

GND

3.3VD

1.8V

Applications Information (Cont.)

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