Applications Information

General Description

The SC620 includes eight (8) independently controlled cur-

rent sinks designed to control LED backlighting for mobile

phones and other battery-operated handheld devices. As

LED forward voltages decrease for white, blue, and other

colored LEDs, there is less need for voltage boosting de-

vices for powering backlight and indicator LEDs. In such

systems where there is a fixed supply voltage large enough

to supply the LEDs or where the LEDs can be powered over

the entire battery range, the SC620 provides a simple low-

cost driver alternative to charge pump or inductor-based

switching boost converters.

Current Sink Design

Each current sink is designed for a pin voltage range be-

tween 150mV and V

to operate backlight LEDs with constant current without

interference caused by blinking indicator LEDs or driving

LEDs with various forward voltages and currents.

Protection Circuitry

The SC620 contains protection circuitry that prevents

the device from operating in an unspecified state. These

features are: Under-voltage Lockout Protection, Over-tem-

perature Protection and Short-circuit Protection.

Under-Voltage Lockout

An Under-voltage Lockout Protection (UVLO) circuit disables

the device in the event that the input voltage falls too low.

UVLO typically occurs at 2V. Hysteresis is provided to pre-

vent chatter.

Short-Circuit Protection

The output sink pins ILED1 through ILED8 are protected

against shorting to V

in the event of a shorted LED. The source lead of each

sink is connected to ground, so the output sink pins do

not require protection against being externally shorted to

ground, as this would result in zero potential across the

sink device.

Over-Temperature Protection

The Over-temperature Protection circuit helps prevent the

device from overheating and experiencing a catastrophic

failure. When the junction temperature exceeds 155°C, the

device is disabled and remains disabled until the junction

temperature drops by the hysteresis value.

Layout Considerations

The MLPQ-UT-16 package has a thermal die attach pad

located at the center. This pad must be connected to the

ground plane through multiple vias as shown (illustration

not to scale).

For low noise, four ground pins are located at the corner

pins 1, 4, 9 and 12. Connect each of the ground pins di-

rectly to the ground plane as shown.

The layout is otherwise quite simple and requires very few

components in addition to the LEDs that it will drive. A 1μF

decoupling capacitor at VIN is required. Place this capacitor

near pin 2, and ground it close to the SC620 as shown.

SCL

SC620

GND

GND

SDA

GND

GND

GND

EN

Ground plane

7

© 2006 Semtech Corp.

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POWER MANAGEMENT

SC620