ACT30

Rev 5, 05-Jun-09

Active-Semi

Innovative Power

TM

- 6 -

www.active-semi.com

Copyright © 2009 Active-Semi, Inc.

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Pulse Modulation

The PFWM Switching Control Logic block operates

in different modes depending on the output load

around 4.75V. The energy delivered by each

switching cycle (with minimum on time of 500ns) to

4.75V. The FPWM Switching Control Logic block is

able to detect this condition and prevents the IC

results in a pulse-modulation action with fixed pulse

width and varying frequency, and low power

consumption because the switching frequency is

reduced.

Typical

system

standby

power

consumption is 0.15W.

Short Circuit Hiccup

When the output is short circuited, the ACT30

enters hiccup mode operation. In this condition, the

auxiliary supply voltage collapses. An on-chip

detector compares DRV1 voltage during the off-

time of each cycle to 6.8V. If DRV1 voltage is below

6.8V, the IC will not start the next cycle, causing

drops below 3.35V. This hiccup behavior continues

until the short circuit is removed. In this behavior,

the effective duty cycle is very low resulting in very

low short circuit current.

To make sure that the IC enters hiccup mode

easily, the transformer should be constructed so

that there is close coupling between secondary and

auxiliary, so that the auxiliary voltage is low when

the output is short-circuited. This can be achieved

with the primary/auxiliary/secondary sequencing

from the bobbin.