CM3842CS datasheet(7/12 Pages) ETC

7 / 12 page

CM3842/3843

CURRENT MODE PWM CONTROLLER

2001/06/27

Advanced

Champion Microelectronic Corporation

Page 6

APPLICATION INFORMATION

Fig. 1. Current Sense Circuit

Peak current (IS) is set by: IS(MAX) = 1V/RS

Fig. 3. Oscillator Section

1.72

Fig. 2. Error Amplifier Configuration - the

amplifier can source or sink up to 0.5mA

For RT < 5K, f =

RTCT

Fig. 4. Open-loop laboratory test fixture: Careful grounding techniques are necessary for high peak

currents associated with capacitive loads. Timing and bypass capacitors should be connected to

GND pin in a single point ground. The transistor and 5K potentiometer are used to sample the

oscillator waveform and apply an adjustable ramp to the ISENSE pin

GND

ISENSE

COMP

Error

Amp

Current

Sense

Comparator

4.7K

Error AMP

Adjust

4.7K

2N2222

100K

ISENSE

Adjust

COMP

VFB

ISENSE

RT/CT

GND

VREF

VCC

Output

0.1

µµµµF

Output

1K,

VCC

VREF

0.1

µµµµF

GND

2.5V

0.5mA

VFB

COMP

Error

Amp

GND

RT/CT

VREF

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