SC628AEVB datasheet(13/21 Pages) SEMTECH

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SC628A

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 affects only the FL pin

and will turn off 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 off, sleep mode is activated. This is a

reduced current mode that helps minimize overall current

consumption by turning off the clock and the charge

pump while continuing to monitor the serial interface for

commands.

I2C Compatible Interface Functions

All device functions can be controlled via the I2C

compatible interface. The interface is described in detail

in the Serial Interface 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 off until V

OUT

is sufficiently 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.

•

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 off state.

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