CS7054 datasheet(3/6 Pages) CHERRY

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Package Lead Description

PACKAGE LEAD #

LEAD SYMBOL

FUNCTION

Application Information

Oscillator

The IC sets up a constant frequency triangle wave at the

COSC lead whose frequency is determined by the external

components ROSC and COSC by the following equation:

Frequency =

The peak and valley of the triangle wave are proportional

to VCC by the following:

VVALLEY = 0.2 ´ VCC

VPEAK = 0.8 ´ VCC

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 COSC must also vary

with supply. ROSC sets up the current which charges COSC.

The voltage across ROSC is 50% of VCC and therefore:

IROSC = 0.5 ´

IROSC is multiplied by two (2) internally and transferred to

the COSC lead. Therefore:

ICOSC = ±

The period of the oscillator is:

T = 2COSC ´

The ROSC and COSC components can be varied to create fre-

quencies over the range of 15Hz to 25kHz. With the sug-

gested values of 105k½ and 390pF for ROSC and COSC

respectively, the nominal frequency will be approximately

20 kHz. IROSC, at VCC = 14V, will be 66.7 µA. IROSC should

not change over a more than 2:1 ratio and therefore COSC

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

(VPEAK - VVALLEY)

ICOSC

VCC

ROSC

VCC

ROSC

0.83

ROSC ´ COSC

Theory Of Operation

14 Lead PDIP

OUTPUT

MOSFET Gate Drive

Gnd

Ground

FLT

Fault time out capacitor

4COSC

Oscillator capacitor

5ROSC

Oscillator resistor

CTL

Pulse width control input

No connection

8VREG

5V linear regulator

9ISENSE-

Current sense minus

ISENSE+

Current sense plus

IADJ

Current limit adjust

INH

Output Inhibit

PGnd

Power ground for on chip clamp

VCC

Positive power supply input

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