Package Lead Description
PACKAGE LEAD #
LEAD SYMBOL
FUNCTION
CS7054
14 Lead PDIP
1
2
3
4
5
6
7
8
9
10
11
12
13
14
OUTPUT
Gnd
FLT
C
OSC
R
OSC
CTL
NC
V
REG
I
SENSE-
I
SENSE+
I
ADJ
INH
PGnd
V
CC
MOSFET Gate Drive
Ground
Fault time out capacitor
Oscillator capacitor
Oscillator resistor
Pulse width control input
No connection
5V linear regulator
Current sense minus
Current sense plus
Current limit adjust
Output Inhibit
Power ground for on chip clamp
Positive power supply input
Application Information
Theory Of Operation
Oscillator
The IC sets up a constant frequency triangle wave at the
C
OSC
lead whose frequency is determined by the external
components R
OSC
and C
OSC
by the following equation:
0.83
R
OSC
´
C
OSC
T = 2C
OSC
´
(V
PEAK
- V
VALLEY
)
I
COSC
I
COSC
= ±
V
CC
R
OSC
I
ROSC
is multiplied by two (2) internally and transferred to
the C
OSC
lead. Therefore:
The period of the oscillator is:
Frequency =
The peak and valley of the triangle wave are proportional
to V
CC
by the following:
V
VALLEY
= 0.2
´
V
CC
V
PEAK
= 0.8
´
V
CC
This is required to make the voltage compensation func-
tion properly. In order to keep the frequency of the oscilla-
tor constant the current that charges C
OSC
must also vary
with supply. R
OSC
sets up the current which charges C
OSC
.
The voltage across R
OSC
is 50% of V
CC
and therefore:
V
CC
R
OSC
The R
OSC
and C
OSC
components can be varied to create fre-
quencies over the range of 15Hz to 25kHz. With the sug-
gested values of 105k�½ and 390pF for R
OSC
and C
OSC
respectively, the nominal frequency will be approximately
20 kHz. I
ROSC
, at V
CC
= 14V, will be 66.7 µA. I
ROSC
should
not change over a more than 2:1 ratio and therefore C
OSC
should be changed to adjust the oscillator frequency.
Voltage Duty Cycle Conversion
The IC translates an input voltage at the CTL lead into a
duty cycle at the OUTPUT lead. The transfer function
incorporates Cherry SemiconductorÕs patented Voltage
Compensation method to keep the average voltage and
current across the load constant regardless of fluctuations
3
I
ROSC
= 0.5
´
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
