SC620 datasheet(10/18 Pages) SEMTECH

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SC620

General Description

The SC620 includes eight independently controlled

current 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 devices for powering backlight and indicator

LEDs. In these types of 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

between 150mV and V

- 1.5V. This feature allows the

system 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

damage from operating in an unspecified state. These

features include:

Under-voltage Lockout Protection

Over-temperature Protection

Short-circuit Protection

Under-Voltage Lockout

An Under-Voltage Lockout Protection (UVLO) circuit dis-

ables the device in the event that the input voltage falls

below the threshold. UVLO typically occurs at 2V.

Hysteresis is provided to prevent chatter.

Short-Circuit Protection

The output sink pins ILED1 through ILED8 are protected

against shorting to V

, prevent device damage in the

event of a shorted LED. The source lead of each sink is con-

nected 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 is reduced.

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).

SCL

VIN

CIN

SC620

GND

SDA

GND

Ground plane

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

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

directly to the ground plane as shown.

The layout is simple and requires very few components in

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

capacitor at the IN pin is required. Place this capacitor

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

Applications Information

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