CURRENT MODE PWM CONTROLLER
Fig.1 Open Loop Test Circuit
LM3842A/3A/4A/5A
V
REF
R
T
4.7K
2N
2222
A
V1
1
E/A
ADJUST
1K
100K
2
I
SENSE
ADJUST
4.7K
C
T
5K
3
COMP
V
REF
V
C
8
0.1
V
FB
7
0.1
1K/1W
LM3842A
I
SENSE
R
T
/C
T
OUTPUT 6
OUTPUT
4
GND
5
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
7
ON/OFF COMMAND
TO REST OF IC
I
CC
LM3842A
V
ON
V
OFF
16V
10V
LM3843A/5A
8.4V
7.6V
< 15mA
< 1mA
V
OFF
V
ON
V
CC
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
2.5V
0.5mA
+
V
FB
Zi
Zf
COMP
2
1
-
Error amp can source or sink up to 0.5mA
HTC
3
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
