CURRENT MODE PWM CONTROLLER
Fig.1 Output Dead Time
80
R
T
, Timing Resister (kΩ
50
C
T
=10nF
C
T
=5.0nF
20
8.0
5.0
2.0
0.8
10k
20k
50k100k
200k
500k
1.0M
3
100
1k
C
T
=2.0nF
C
T
=1.0nF
C
T
=500pF
C
T
=200pF
C
T
=100pF
30
100
LM3842A/3A/4A/5A
Fig.2 Timing Resistor vs Frequency
C
T
=100nF
C
T
=47nF
R
T
(kΩ)
C
T
=22nF
C
T
=10nF
10
C
T
=4.7nF
C
T
=2.2nF
C
T
=10nF
fosc, Frequency (kHz)
10k
100k
1M
fosc, Frequency(Hz)
Fig.3 Output Saturation Characteristics
Fig.4 Error Amplifier Open Loop
Gain and Phase Frequency
V
SAT
, Output Saturation Voltage (V
4
V
CC
=15V
T
A
=25℃
3
A
VOL
, Open-Loop Voltage Gain (d
80
Gain
60
0
Φ, Excess Phase Degree
-45
2
40
Phase
-90
1
SOURCE (V
C
-V
OH
)
C
20
-135
SINK (V )
OL
0
-180
0
10
-3
2
4
6 8 10
-1
2
4
6 8
10
100
1K
10K 100K
1M
10M
Io, Output Load Current (A)
Fosc, Frequency (Hz)
PIN FUNCTION DESCRIPTION
Pin No.
1
2
3
4
Function
Description
Compensation This pin is the Error Amplifier output and is made available for loop
compensation.
Voltage
This is the inverting input of the Error Amplitier. It is normally connected
Feedback
to the switching power supply output through a resister divider.
Current Sense A voltage proportional to inductor current is connected to this input.
The PWM uses this information to terminate the output switch conduction.
R
T
/C
T
The Oscillator frequency and maximum Output duty cycle are
programmed by connecting resistor R
T
to VR
EF
and capacitor C
T
to ground. Operation to 500kHz is possible.
GND
This pin is the combined control circuitry and power ground.
Output
This output directly drives the gate of a power MOSFET. Peak currents
up to 1.0A are sourced and sunk by this pin.
Vcc
This pin is the positive supply of the control IC.
V
REF
This is the reference output. It provides charging current for capacitor
C
T
through resistor R
T
.
5
6
7
8
HTC
6
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
