Typical Performance Characteristics
100
90
900
800
700
600
500
400
300
200
100
R
T =680Ω
80
70
60
50
40
RT =1.5kΩ
30
20
10
RT =10kΩ
.0005
.001
.002 .003
.005
.01
.02
.03 .04 .05
100
200 300 400 500 700 1k
RT (Ω)
2k
3k 4k 5k 7k 10k
CT (µF)
Oscillator Frequency vs CT
Oscillator Duty Cycle vs RT
Test Circuit Open Loop Laboratory Test Fixture
VREF
RT
2N2222
VCC
A
100kΩ
COMP
VFB
VREF
4.7kΩ
0.1µF
0.1µF
1kΩ
Error Amp
Adjust
VCC
1kΩ
1W
5kΩ
Sense
Adjust
4.7kΩ
VOUT
VOUT
Sense
OSC
Gnd
Gnd
CT
Circuit Description
Undervoltage Lockout
VCC
ON/OFF Command
to reset of IC
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.
VON =8.4V
V
OFF = 7.6V
PWM Waveform
ICC
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
<15mA
2). An increase in V causes the inductor current slope to
CC
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.
<500µA
VCC
VON VOFF
Figure 1: Startup voltage for the CS52843.
4
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
