CS1108
CS1108
Single Lamp Driver IC
Description
This ASIC provides up to 350mA of
drive current for powering bulbs.
The typical application for this part
is for use in airbag systems using a
type 194 bulb. On chip diagnostics
provide open circuit and short cir-
cuit detection in the output on
mode. In addition, the output
driver will turn on (sink current)
when V
CC
is low. Fault is an
active-low output which reports in
the output-on mode. Internal pull-
up circuitry is provided to ensure
the output pin turns on when the
Control pin is floating.
Features
s
Fault Detection
Open Circuit
Short Circuit
Over Temperature
s
V
CC
Sense: Output Turns
On with Loss of V
CC
s
Low Standby Current
Absolute Maximum Ratings
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65ûC to 150ûC
V
CC
, Fault , Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to 6V
ESD Capability (Human Body Model). . . . . . . . . . . . . . . . . . . . . . . . . . . 2kV
Peak Transient Voltage (output off mode, output pin only)
(26V load Dump @ 14V V
BAT
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40V
Lead Temperature Soldering
Reflow (SMD styles only) . . . . 60 sec. max above 183¡C, 230¡C peak
Block Diagram
V
CC
V
CC(SENSE)
I
SOURCE
Output
Drive
& Bias
Control
Overtemp
Shutdown
Package Options
8 Lead SO
(internally fused leads)
Output
V
CC
1
Duty cycle
during
short circuit
Gnd
Gnd
Gnd
Gnd
+
Fault
-
-
+
short circuit
detect
open circuit
detect
Fault
Control
Gnd
Gnd
Gnd
Gnd
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
Rev. 12/28/98
1
A
¨
Company
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
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