CS1108 datasheet(3/4 Pages) CHERRY

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VBAT

VCC

Output

Gnd

VCC

Control

Gnd

CS1108

Gnd

Fault

microprocessor

20k

10nF

Applications Diagram

Circuit Description

The CS1108 lamp driver IC provides up to 350mA of drive

current in a low-side configuration. The Output driver pin

is controlled through the TTL compatible Control input

pin. A high condition on the Control pin turns the output

pin on.

The

pin reports short circuit, open circuit, and

overtemperature conditions on the IC. If a fault is present,

the open collector output

pin will be low. Typical

numbers for faults are: exceeding 500mA of drive current

will report a short circuit. Less than 40mA (typical) will

report an open circuit. A temperature fault will be reported

when the die temperature exceeds 180¡C (typical). Faults

are only reported when the Control pin is high, due to the

low quiescent current when the Control pin is low and the

output device is turned off.

The CS1108 is designed to provide overcurrent protection

by duty cycle control. When the lamp current exceeds the

internally programmed current limit threshold (typically

500mA), the output enters duty cycle mode to reduce

power dissipation of the IC to a safe level.

Typical lamps have a low resistance when off and the cur-

rent will exceed the current limit threshold during the ini-

tial inrush period. During this inrush time, the IC will be

operating in the duty cycle mode. Due to characteristics of

lamps in this mode, they may appear dimly lit. This condi-

tion will persist for a brief time until the lamp resistance

has increased enough to reduce itÕs current below the

threshold. Once this occurs the lamp will appear at full

brightness. During the inrush period the Fault pin will be

forced low indicating that duty cycle mode is in operation.

Thermal protection has been designed into this IC. Should

duty cycle mode operate for an extended amount of time

and the power limitations of the IC are exceeded the IC die

temperature will rise. Once the die temperature reaches the

thermal temperature limit, the internal circuitry will shut-

off the output and the lamp will turn off. Once the die tem-

perature lowers below the thermal threshold then the out-

put will be allowed to turn back on.

Fault

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