SC628A
13
Applications Information (continued)
timer’s default state is on, but the timer may be disabled
via the serial interface to allow continuous output current
in spotlight mode. The safety timer a ects only the FL pin
and will turn o the sink after a period of 1 second. The
timer may be reset by either forcing the FLEN pin low
or by resetting the Flash/Spotlight control bits via the
interface.
Shutdown State
The device is disabled when the EN pin is low. All registers
are reset to default condition when EN is low.
Sleep Mode
When the LED is o , sleep mode is activated. This is a
reduced current mode that helps minimize overall current
consumption by turning o the clock and the charge
pump while continuing to monitor the serial interface for
commands.
I
2
C Compatible Interface Functions
All device functions can be controlled via the I
2
C
compatible interface. The interface is described in detail
in the Serial I
nterface section of the datasheet.
Protection Features
The SC628A provides several protection features to
safeguard the device from catastrophic failures. These
features include:
Output Open Circuit Protection
Over-Temperature Protection
Charge Pump Output Current Limit
LED Float Detection
Output Open Circuit Protection
Over-Voltage Protection (OVP) is provided at the OUT
pin to prevent the charge pump from producing an
excessively high output voltage. In the event of an open
circuit at OUT, the charge pump runs in open loop and
the voltage rises up to the OVP limit. OVP operation is
hysteretic, meaning the charge pump will momentarily
turn o until V
OUT
is su ciently reduced. The maximum
OVP threshold is 6.0V, allowing the use of a ceramic
output capacitor rated at 6.3V with no fear of over-voltage
damage.
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•
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Over-Temperature Protection
The Over-Temperature (OT) protection circuit helps
prevent the device from overheating and experiencing
a catastrophic failure. When the junction temperature
exceeds 160 °C, the device goes into thermal shutdown
with all outputs disabled until the junction temperature
is reduced. All register information is retained during
thermal shutdown.
Charge Pump Output Current Limit
The device also limits the charge pump current at the
OUT pin. When OUT is shorted to ground, the typical
output current is 400mA. The current limiting is triggered
by an output under-voltage lockout below 2V. The output
returns to normal when the short is removed and OUT is
above 2.5V. Above 2.5V, a minimum current limit of
1000mA applies.
LED Float Detection
Float detect is a fault detection feature of the LED current
sink output. If the output is programmed to be enabled
and an open circuit fault occurs on the current sink, the
resulting open loop will cause the output voltage to
change to the default condition V
OUT
= 3.0V. The output
will remain 3.0V until the loop is once again completed by
an LED or the output is re-programmed to the o state.
