SP6415 Datasheet, PDF (6/12 Pages) Sipex Corporation – Integrated White LED Driver With Organic LED Display Power Supply

The SP645 is designed for white LED & OLED back-
lighting in mobile phone applications. It has a main
display loop which can drive up to 4 white LEDS in series
and a SUB display loop which is designed to drive OLED
up to 20V/0mA or 3 white LEDs.
The SP645 operates at a wide input voltage range
suitable for Li-ion battery and has a constant off time
for smaller inductor and capacitors. The block diagram
refers the operation circuit. By SEL pin, it can choose the
different channel to turn on CH or CH2.
Current Limit Protection
The SP645 has current limiting protection to prevent
excessive stress on itself and external components dur-
ing overload conditions. The internal current limit com-
parator will disable the NMOS power device at a typical
switch peak current limit of 300mA.
Detailed Description
Output Over-Voltage Protection
The SP645 contains dedicated circuitry for
monitoring the output voltage. In the event that the
primary LED network is disconnected the output will
increase and be limited to 22V(typ.). There is a ~V
hysteresis associated with this circuitry, which will turn
the NMOS off when the output voltage is at 23V(max.)
until the output voltage reach 2V(typ.) or lower. The
22V limit allows the use of 25V µF ceramic output
capacitors creating an overall small solution for white
LED applications.
Under Voltage Protection
The SP645 has a UVP comparator to turn the NMOS
power device off in case the input voltage or battery voltage
is too low,preventing an on state of the power device con-
ducting large amounts of current. There is a ~V hysteresis
associated with this circuitry, which will turn the NMOS off
when the output voltage is at 23V(max.) until the output
voltage reaches 2V(typ.) or lower. The 22V limit allows
the use of 25V mF ceramic output capacitors creating an
overall small solution for white LED applications.
Inductor Selection
The recommended value of inductor for SP645ap-
plications is 0uH. Small size and better efficiency are
the major concerns for portable device, such as SP645
used for dual panel mobile phone. The inductor should
have low DCR for better efficiency. To avoid inductor
saturation, current rating should be at least 600mA. The
input range is 2.7V to 5.5V.
Capacitor Selection
A 4.7µF input capacitor can reduce input ripple. For
better voltage stability, to increase the input capacitor
value or using an LC filter is feasible, especially in Li-
Ion battery applications. The input capacitor acts as a
bypass to the IC and needs to be connected directly to
the VIN pin and the GND pin for proper low ripple reg-
ulation.
Application Information
The output capacitor needs to be a minimum of uF
with 25V rating. For applications with 5V input, an
output capacitor of 2.2uF or 4.7uF may be needed to
lower output ripple and improve regulation. For better
voltage filtering, ceramic capacitors with low ESR are
recommended. X5R and X7R types are suitable be-
cause of their wider voltage and temperature ranges.
Diode Selection
A Schottky diode is a good choice for SP645
because of its lower forward voltage drop and faster
reverse recovery. Using Schottky diodes can help ob-
tain better efficiency. High speed rectification is also a
good characteristic of Schottky diodes for high switch-
ing frequency. Current rating of the diode must meet
the root mean square of the peak current and output
average current multiplication.
Feb27-07 Rev K
Integrated White LED Driver With Organic LED Display Power Supply

© 2007 Sipex Corporation