CS52843
Typical Performance Characteristics
100
90
900
800
R
T
=680Ω
700
80
DUTY CYCLE (%)
70
60
50
40
30
FREQ. (kHz)
600
500
R
T
=1.5kΩ
400
300
200
100
R
T
=10kΩ
20
10
.0005
.001
.002
.003
.005
.01
.02
.03 .04 .05
100
200
300 400 500 700
1k
2k
3k 4k 5k
7k
10k
C
T
(µF)
R
T
(Ω)
Oscillator Frequency vs C
T
Oscillator Duty Cycle vs R
T
Test Circuit Open Loop Laboratory Test Fixture
V
REF
R
T
2N2222
100kΩ
4.7kΩ
1kΩ
Error Amp
Adjust
4.7kΩ
5kΩ
A
COMP
V
REF
0.1µF
V
CC
V
FB
V
CC
0.1µF
1kΩ
1W
Sense
Adjust
Sense
V
OUT
V
OUT
OSC
Gnd
Gnd
C
T
Circuit Description
V
CC
Undervoltage Lockout
ON/OFF Command
to reset of IC
V
ON
=8.4V
V
OFF
= 7.6V
During Undervoltage Lockout (Figure 1), the output driv-
er is biased to sink minor amounts of current. The output
should be shunted to ground with a resistor to prevent
activating the power switch with extraneous leakage cur-
rents.
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.
4
I
CC
<15mA
<500µA
V
ON
V
OFF
V
CC
Figure 1: Startup voltage for the CS52843.
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
