參數(shù)資料
型號: CS2842A
廠商: ZF Electronics Corporation
英文描述: Off-Line Current Mode PWM Control Circuit with Undervoltage Lockout
中文描述: 離線式電流模式PWM控制電路欠壓鎖定
文件頁數(shù): 4/6頁
文件大?。?/td> 156K
代理商: CS2842A
4
C
V
REF
V
CC
V
OUT
1k
1W
0.1
μ
F
0.1
μ
F
V
REF
V
CC
V
OUT
Gnd
V
FB
Sense
OSC
COMP
5k
100k
4.7k
1k
ERROR AMP
ADJUST
4.7k
Sense
ADJUST
R
T
2N2222
C
T
Gnd
A
Test Circuit
Undervoltage Lockout
During Undervoltage Lockout (Figure 1), the output driv-
er is biased to a high impedance state. The output should
be shunted to ground with a resistor to prevent output
leakage current from activating the power switch.
PWM Waveform
To generate the PWM waveform, the control voltage from
the error amplifier is compared to a current sense signal
which represents the peak output inductor current (Figure
2). An increase in V
CC
causes the inductor current slope to
increase, thus reducing the duty cycle. This is an inherent
feed-forward characteristic of current mode control, since
the control voltage does not have to change during
changes of input supply voltage.
When the power supply sees a sudden large output cur-
rent increase, the control voltage will increase allowing the
duty cycle to momentarily increase. Since the duty cycle
tends to exceed the maximum allowed to prevent trans-
V
CC
ON/OFF Command
to reset of IC
V
ON
16V 8.4V
V
OFF
10V 7.6V
CSX842A CSX843A
<15mA
<1mA
V
ON
V
OFF
I
CC
V
CC
Circuit Description
Typical Performance Characteristics
.0005
.001
.002
.003
.005
.01
.02
.03
.04
800
900
F
C
T
(
μ
F)
700
600
500
400
300
200
100
.05
R
T
=1.5k
R
T
=680
R
T
=10k
100
200
700
1k
2k
5k
7k
10k
80
90
D
R
T
(
)
70
60
50
40
30
20
10
4k
3k
500
400
300
100
Oscillator Duty Cycle vs R
T
Oscillator Frequency vs C
T
Figure 1: Typical Undervoltage Characteristics
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