CR6202 Просмотр технического описания (PDF) - Unspecified

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CR6202

Switching Power Supply Controller ICs

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CR6202

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

improved). In the open or closed cycle, if power transistor is detected to exceed upper limit current, the

upper limit current trigger will set firstly and forces FB to pull down, duty cycle reduced, so to protect

power transistor and transformer. In the next closed cycle start-up time, or when FB is less than 1.8V,

upper current trigger resets. In addition, CR6202 is built in thermal protection, when the internal

temperature is above 125ć, it will widen the cycle of oscillator, so that the temperature of CR6202 will

not exceed 135ć. Slop compensation is built in to stabilization open/closed cycle during the maximum

duty cycle or the continual current mode of CR6202.

If VCC reduces to 4.4V, oscillator is turn off, OSC1 OSC2 low level, power supply keeps closed cycle.

when VCC continually reduces to about 3.6 V , CR6202 enters start-up phase again.

Definition of Electric Parameter

Start-up acceptance current: the current on OC when OB inputs 0.5mA during the start-up phase

Start-up Quiescent Current: the current of minimum current source that can make VCC oscillate (namely

finish the start-up of CR6202) when VCC meets filter capacitance and adjustable current source, CT meets

330PF, and other pins no connected.

Start-up Voltage: Maximum VCC value of above VCC oscillation.

Re-start Voltage: Minimum VCC value of above VCC oscillation.

Aug.2008 V2.0

6/14

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