SC627_09 Datasheet, PDF (14/23 Pages) Semtech Corporation – LED Light Management Unit Charge Pump, 4 LEDs, 700mA Flash LED, Dual LDOs, and SemWireTM Interface

SC627
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 700mA for a flash LED or array of parallel
LEDs. Flash current settings are in 50mA increments from
50mA to 700mA. 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 SC627 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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