SC624
13
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
e ciency 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 coe cients
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 o , sleep mode is activated. This is a
reduced current mode that helps minimize overall current
consumption by turning o 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 o until V
OUT
is su ciently 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.
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