ICE3AS02 datasheet(9/22 Pages) INFINEON

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ICE3AS02 / ICE3AS02G / ICE3BS02 / ICE3BS02G

Functional Description

Version 1.2

02 Sep 2005

When Active Burst Mode is entered, the internal Bias is

switched off in order to reduce the current consumption to

below 1.05mA while keeping the Voltage Reference active

as this is necessary in this mode.

3.3

Startup Phase

Figure 5

Soft Start

At the beginning of the Startup Phase, the IC provides a Soft

Start duration whereby it controls the maximum primary

current by means of a duty cycle limitation. A signal VSoftS

which is generated by the external capacitor CSofts in

combination with the internal pull up resistor RSoftS,

determines the duty cycle until VSoftS exceeds 4V.

When the Soft Start begins, CSoftS is immediately charged up

to approx. 1V by T2. Therefore the Soft Start Phase takes

place between 1V and 4V. Above VSoftsS = 4V there is no

longer duty cycle limitation DCmax which is controlled by

comparator C7 since comparator C2 blocks the gate G7 (see

Figure 5). This maximum charge current in the very first

stage when VSoftS is below 1V, is limited to 1.32mA.

Figure 6

Startup Phase

By means of this extra charge stage, there is no delay in the

beginning of the Startup Phase when there is still no

switching. Furthermore Soft Start is finished at 4V to have

faster the maximum power capability. The duty cycles DC1

and DC2 are depending on the mains and the primary

inductance of the transformer. The limitation of the primary

current by DC2 is related to VSoftS = 4V. But DC1 is related

to a maximum primary current which is limited by the

internal Current Limiting with CS = 1V. Therefore the

maximum Startup Phase is divided into a Soft Start Phase

until t1 and a phase from t1 until t2 where maximum power

is provided if demanded by the FB signal.

Soft-Start

Comparator

Soft Start

SoftS

3.25k

Ω

6.5V

SoftS

Gate Driver

0.85V

x3.7

PWMOP

max

SoftS

max. Soft Start Phase

5.4V

max. Startup Phase

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