CS1108

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CIRCUIT DESCRIPTION

The CS1108 lamp driver IC provides up to 350 mA 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 Fault pin reports short circuit, open circuit, and

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

the open collector output Fault pin will be low. Typical

numbers for faults are: exceeding 500 mA of drive current

will report a short circuit. Less than 40 mA (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

500 mA), 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

current will exceed the current limit threshold during the

initial 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

condition will persist for a breif time until the lamp

resistance has increased enough to reduce it’s 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 cicuitry will shutoff

the output and the lamp will turn off. Once the die temperature

lowers below the thermal threshold, the output will be

allowed to turn back on.

Figure 2. Applications Diagram

10 nF

20 k

Output

Fault

Control

GND

GND

GND

GND

CS1108

microprocessor