SC620_09 Datasheet, PDF (10/18 Pages) Semtech Corporation – Octal LED Driver,General Purpose Current Sink With Serial Interface

SC620
Applications Information
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
IN
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_IN, 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.
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).
Ground plane
SC620
GND
GND
C_IN
EN
GND
SCL
SDA
V_{IN GND}
GND
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.
Over-Temperature Protection
The Over-temperature Protection circuit helps prevent the
device from overheating and experiencing a catastrophic
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