CS1108
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 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 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.
Applications Diagram
Output
10nF
V
CC
Fault
20k
Control
V
BAT
V
CC
CS1108
Gnd
Gnd
Gnd
Gnd
microprocessor
3
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
