SC624 Ver la hoja de datos (PDF) - Semtech Corporation

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SC624

LED Light Management Unit Charge Pump, 4 LEDs, Dual LDOs, and SemWire™ Interface

Semtech Corporation 

SC624

Applications Information (continued)

Backlight Quiescent Current

The quiescent current required to operate all four

backlights is reduced by 1.5mA when backlight current

is set to 4.0mA or less. This feature results in higher

efficiency under light-load conditions. Further reduction

in quiescent current will result from using fewer than four

LEDs.

Fade-In and Fade-Out

Backlight brightness can be set to automatically fade-in

when current is set to increase and fade-out when current

is set to decrease. When enabled with a new current

setting, the current will step through each incremental

setting between the old and new values. The result is a

visually smooth change in brightness with a rate of fade

that can be set to 8, 16, 24, or 32 ms per step.

Programmable LDO Outputs

Two low dropout (LDO) regulators are provided for

camera module I/O and core power. Each LDO has at least

100mA of available load current with ±3.5% accuracy. The

minimum current limit is 200mA, so outputs greater than

100mA are possible at somewhat reduced accuracy.

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 all LEDs are 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 SC624 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 is sufficiently reduced. The maximum

OUT

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.

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