CURRENT MODE PWM CONTROLLER

LM3842A/3A/4A/5A

Fig.1 Open Loop Test Circuit

High peak currents associated with capacitive loads necessitate careful grounding techniques

Timing and bypass capacitors should be connected close to pin 5 in a single point ground.

The transistor and 5KΩ potentiometer are used to sample the oscillator waveform and apply an

adjustable ramp to pin 3.

Fig.2 Under Voltage Lockout

LM3842A

LM3843A/5A

16V

8.4V

10V

7.6V

During Under-Voltage Lock-Out, the output driver is biased to a high impedance state.

Pin 6 should be shunted to ground with a bleeder resistor to prevent activating the power switch

with output leakage current.

Fig.3 Error Amp Configuration

HTC

3

1

2

3

4

8

7

6

5

COMP

OUTPUT

GND

LM3842A

0.1

0.1

A

OUTPUT

1K/1W

V1

100K

2N

2222

4.7K

1K

5K

ADJUST

4.7K

E/A

ADJUST

Error amp can source or sink up to 0.5mA

2

1

-

+

Zi

Zf

COMP

0.5mA

2.5V

7

ON/OFF COMMAND

TO REST OF IC

< 15mA

< 1mA