SC622 datasheet(14/21 Pages) SEMTECH

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SC622

Applications Information (continued)

A 1μF, low ESR capacitor should be used as a bypass

capacitor on each LDO output to reduce noise and

ensure stability. In addition, it is recommended that a

minimum 22nF capacitor be connected from the BYP

pin to ground to minimize noise and achieve optimum

power supply rejection. A larger capacitor can be used

for this function, but at the expense of increasing turn-

on time. Capacitors with X7R or X5R ceramic dielectric

are strongly recommended for their low ESR and superior

temperature and voltage characteristics. Y5V capacitors

should not be used as their temperature coefficients

make them unsuitable for this application.

Shutdown State

The device is disabled when the SWIF pin is low. All

registers are reset to default condition when SWIF 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. Both LDOs can be powered up while in sleep

mode.

SemWire Single Wire Interface Functions

All device functions can be controlled via the SemWire

single wire interface. The interface is described in detail

in the SemWire Interface section of the datasheet.

Protection Features

The SC622 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.

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 1A applies.

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 output. If the output is programmed to be enabled

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

the output will be disabled to prevent a sustained output

OVP condition from occurring due to the resulting open

loop.

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