CR6202 Просмотр технического описания (PDF) - Unspecified

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CR6202

Switching Power Supply Controller ICs

Unspecified 

CR6202

Pin Assignment & Description

Name

CT

FB

GND

OC

OE

OB

VCC

Description

By connecting a cap to ground to set the switching

frequency

Feedback pin

GND

Power Transistor collector drive output and start-up

current input.

Power Transistor Emitter drive output and start-up

current input.

Power Transistor Base drive output and start-up

current control.

Power Supply.

Operation description

Initially, after power up, FB pull-up current source is turn off. OC inputs start-up current from power

transistor to VCC. OB controls the base current of power transistor and limits the collector current

(start-up accept current of CR6202) of power transistor so to safeguard the power transistor. When the

VCC voltage rises to 10.2V, the start-up phase completes and goes to the normal operation.

In normal operation, VCC voltage must keep 4.8~9V,FB pull-up current source turns on. Oscillator

outputs OSC1 to decide the maximum duty cycle and OSC2 to trigger power supply entering the open

cycle and cover spike value of power transistor start-up current. If FB is less than 1.8V(about 1.2-1.8V),

the less the FB is, the wider the oscillation cycle is.（This characteristics reduces the standby consumption

of the switching power supply）. If external feedback intends to get VCC greater than 11.4V, the internal

feedback circuit regular VCC on 11.4V.（Making use of this characteristics to stable output voltage no

using external feedback circuit, but the regulating is not precise）.

In open cycle, OB provides the base current for power transistor, OE pulls down the emitter of power

transistor to IS and OB adopts slop current drive (OB open current is IS function, when IS=0V,OB open

current is about 24mA, and OB open current is increasing with IS linear increasing. When IS increases

0.6V, OB open current is about 40mA. This characteristics makes use of output current of OB effectively

and reduces power consumption of CR6202). If IS detects the FB designated current, it enters closed cycle.

In closed cycle, OB pulls down, the power transistor is not be turn off immediately but OE clamps 1.5V

(after power transistor is turn off, the base is reverse bias, the breakdown voltage of power transistor is

Jun.2008 V1.2

3/7

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