SC621 datasheet(14/23 Pages) SEMTECH

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SC621

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.

LED Flash and Spotlight Current Sink

A single output current sink is provided to drive both flash

and spotlight functions. In flash mode, this current sink

provides up to 400mA for a flash LED or array of parallel

LEDs. Flash current settings are in 50mA increments from

50mA to 400mA. The FLEN pin directly triggers the FLASH

function when pulled high, or it can be wired to VIN to

enable software control via the serial interface.

In spotlight mode, the output can be set for up to 250mA

of continuous current. Settings are available in 50mA

increments from 50mA to 250mA. Continuous operation

above 250mA is not recommended due to high power

dissipation.

Flash and Spotlight Safety Timer

A safety timer disables the flash and spotlight output

current sink if the sink remains active for an extended

period. The timer protects the SC621 and the LED from

high power dissipation that can cause overheating. The

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.

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.

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