AMC384XBDF datasheet(6/10 Pages) ETC

6 / 10 page

AMC DOC. #: AMC3842B_C (LF)

AMC3842B/43B

March

2004

CURRENT MODE PWM CONTROLLER

www.addmtek.com

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

Error

Amp

Current

Sense

Comparator

COMP

ISENSE

GND

VREF

2.5V

0.5mA

Error

Amp

RT/CT

VFB

GND

COMP

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

VREF

VCC

2N2222

4.7K

100K

VREF

COMP

0.1

µF

Error AMP

Adjust

1K,

VFB

VCC

ISENSE

Adjust

Output

ISENSE Output

4.7K

0.1

µF

RT/CT

GND

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