SC621 datasheet(15/23 Pages) SEMTECH

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SC621

Protection Features

The SC621 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

LDO Current Limit

LED Float Detection

Output Open Circuit Protection

Over-Voltage Protection (OVP) is provided at the VOUT

pin to prevent the charge pump from producing an

excessively high output voltage. In the event of an open

circuit at VOUT, 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.

•

Applications Information (continued)

Charge Pump Output Current Limit

The device also limits the charge pump current at

the VOUT pin. When VOUT is shorted to ground, the

typical output current limit is 300mA. The current limiting

is triggered by an output under-voltage lockout below 2V.

The output returns to normal when the short is removed

and VOUT is above 2.5V. Above 2.5V, a typical current

limit of 300mA applies when the FL current sink is off and

a typical current limit of 1A applies when the FL current

sink is on.

LDO Current Limit

The device limits the output currents of LDO1 and LDO2 to

help prevent it from overheating and to protect the loads.

The minimum limit is 200mA, so load current greater than

the rated 100mA can be used with degraded accuracy

and larger dropout without tripping the current limit.

LED Float Detection

Float detect is a fault detection feature of the LED current

sink outputs. If an output is programmed to be enabled

and an open circuit fault occurs at any current sink output,

that output will be disabled to prevent a sustained output

OVP condition from occurring due to the resulting open

loop. Float detect ensures device protection but does

not ensure optimum performance. Unused LED outputs

must be disabled to prevent an open circuit fault from

occurring.

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