CURRENT MODE PWM CONTROLLER
Fig.3 Error Amp Configuration
2.5V
LM3842A/3A/4A/5A
0.5mA
+
V
FB
Zi
Zf
COMP
2
1
-
Error amp can source or sink up to 0.5mA
Fig.4 Current Sense Circuit
ERROR
AMP
I
S
2R
1
R
COMP
CURRENT
SENSE
R
1V
CURRENT
SENSE
COMPARATOR
3
C
R
S
GND
5
Peak current (I
S
) is determined by the formula:
I
S(MAX)
~
1.0V
R
S
A small RC filter may be required to suppress switch transients.
Fig.5 Oscillator Waveforms and Maximum Duty Cycle
V
REF
8
R
T
R
T
/C
T
INTERNAL CLOCK
4
C
T
GND
5
INTERNAL CLOCK
LARGE R
T
SMALL C
T
V
4
LARGE R
T
SMALL C
T
V
4
HTC
−
4
−