2AS01 datasheet(8/24 Pages) INFINEON

8 / 24 page

Datasheet

30 Jun 2006

Preliminary Data

ICE2AS01/S01G

ICE2BS01/S01G

Functional Description

The primary current is sensed by the series resistor

RSense inserted in the source of the external Power

Switch. By means of Current Mode the regulation of the

secondary voltage is insensitive on line variations. Line

variation causes variation of the increasing current

slope which controls the duty cycle.

The external RSense allows an individual adjustment of

the maximum source current of the external Power

Switch.

Figure 6

Improved Current Mode

To improve the Current Mode during light load

conditions the amplified current ramp of the PWM-OP

is superimposed on a voltage ramp, which is built by

the switch T2, the voltage source V1 and the 1st order

low pass filter composed of R1 and C1 (see Figure 6,

Figure 7). Every time the oscillator shuts down for max.

duty cycle limitation the switch T2 is closed by VOSC.

When the oscillator triggers the Gate Driver T2 is

opened so that the voltage ramp can start (see Figure

7).

In case of light load the amplified current ramp is to

small to ensure a stable regulation. In that case the

Voltage Ramp is a well defined signal for the

comparison with the FB-signal. The duty cycle is then

controlled by the slope of the Voltage Ramp.

By means of the C5 Comparator the Gate Driver is

switched-off until the voltage ramp exceeds 0.3V. It

allows the duty cycle to be reduced continuously till 0%

by decreasing VFB below that threshold.

Figure 7

Light Load Conditions

3.2.1

PWM-OP

The input of the PWM-OP is applied over the internal

leading edge blanking to the external sense resistor

RSense connected to pin ISense. RSense converts the

source current into a sense voltage. The sense voltage

is amplified with a gain of 3.65 by PWM OP. The output

of the PWM-OP is connected to the voltage source V1.

The voltage ramp with the superimposed amplified

current signal is fed into the positive inputs of the PWM-

Comparator, C5 and the Soft-Start-Comparator.

3.2.2

PWM-Comparator

The PWM-Comparator compares the sensed current

signal of the external Power Switch with the feedback

signal VFB (see Figure 8). VFB is created by an external

optocoupler or external transistor in combination with

the internal pullup resistor RFB and provides the load

information of the feedback circuitry. When the

amplified current signal of the external Power Switch

exceeds the signal VFB the PWM-Comparator switches

off the Gate Driver.

x3.65

PWM OP

0.8V

10k

Ω

Oscillator

PWM Comparator

20pF

PWM-Latch

0.3V

Gate Driver

Voltage Ramp

OSC

Soft-Start Comparator

OSC

0.8V

Gate Driver

Voltage Ramp

max.

Duty Cycle

0.3V

2AS01 Datasheet(PDF) 8 Page - Infineon Technologies AG

2AS01 Datasheet(HTML) 8 Page - Infineon Technologies AG

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL