AP2002

Synchronous PWM Controller

Anachip Corp.

www.anachip.com.tw

Rev. 0.2 Apr 14, 2004

6/7

Hiccup Mode

During power up, the SS/ SHDN pin is internally

the SS/ SHDN pin is released and begins to source

10uA of current to the external soft-start capacitor.

As the soft-start voltage rises, the output of the

internal error amplifier is clamped to this voltage.

When the error signal reaches the level of the

internal triangular oscillator, which swings from 1V

to 2V at a fixed frequency of 200KHz, switching

occurs. As the error signal crosses over the

oscillator signal, the duty cycle of the PWM signal

continues to increase until the output comes into

regulation. If an over-current condition has not

occurred the soft-start voltage will continue to rise

and level off at about 2.2V.

An

over-current

condition

occurs

when

the

high-side drive is turned on, but the PHASE node

does not reach the voltage level set at the OCSET

pin. The PHASE node is sampled only once per

cycle during the vally of the triangular oscillator.

Once an over-current occurs, the high-side drive is

turned off and the low-side drive turns on and the

SS/ SHDN pin begins to sink 2uA. The soft-start

voltage will begin to decrease as the 2uA of current

discharge the external capacitor. When the

soft-start voltage reaches 0.8V, the SS/ SHDN pin

will begin to source 10uA and begin to charge the

external capacitor causing the soft-start voltage to

rise again. Again, when the soft-start voltage

reaches the level of the internal oscillator, switching

will occur.

If the over-current condition is no longer present,

normal operation will continue. If the over-current

condition is still present, the SS/ SHDN pin will

again begin to sink 2uA. This cycle will continue

indefinitely until the over-current condition is

removed.

In conclusion, above is shown a typical “12V

Application Circuit” which has a BSTH voltage

derived by bootstrapping input voltage to the

PHASE node through diode D1. This circuit is very

useful in cases where only input power of 5V(or

12V) is available.

In

order

to

prevent

substrate

glitching,

a

small-signal diode should be placed in close

proximity to the chip with cathode connected to

PHASE and anode connected to PGND.

Marking Information

( Top View )

SOP-14L

1

8

7

AC

AP2002

YY WW X X

Logo

ID code: internal

Year: "01" = 2001

"02" = 2002

Xth week: 01~52

14

Part No.

Blank: normal

L: Lead Free Package