ICE1QS01

Version 1.4

7

27 Apr 2004

Soft start

begins to work with soft start mode. Soft start is realized with an internal soft start resistor, an inter-

nal current sink, a current source and the external feedback capacitor connected at pin SRC. The

internal resistor is connected between the internal voltage reference and pin SRC. The current sink

is connected between pin SRC and GND. The value of the current is set with a timer. Immediately

rent source is switched off 12 µsec after beginning of soft start. The current value of the current sink

increase stepwise. The soft start is finished 24 msec after the IC is switched on. At the end of the

soft start the current sink is switched off.

Figure: Soft Start

PCS (primary current simulation)

A voltage proportional to the current of the power transistor is generated at Pin PCS by the RC-com-

bination R2, C2. The voltage at Pin PCS is forced to 1.5V when the power transistor is switched off

ton

tp1

tp2

VCCon

VSRC1

VSRC2

VSRC

VCC

t

t

20k

pin SRC

current

sink

up

down

counter

D/A

timer

tp=3ms

2.5V

ICE1QS01

timer

t=12us

500

5V

timer

t=24ms