SP1820
Four Channels Constant Current LED Driver
APPLICATION INFORMATION
CIRCUIT DESCRIPTION
SP1820 is a four channels white-LED driver with matching current output. The matching current regulator has a
460:1 ratio between ILED and ISET. SP1820 is capable to supply 25mA for each channel with proper selection of
external resistor. The design has a band gap regulator, voltage to current converter and mirror drivers.
THERMAL PROTECTION
SP1820 has a thermal comparator to shut down the device when the internal temperature reaches 150℃. It will
remain shut down until the temperature drops to 130℃.
ENABLE
SP1820 has an enable pin that is designed for TTL input. The device will be active at voltage high. This pin can
also be used to control the brightness of LED with a PWM signal. The brightness is proportional to the duty cycle
of the PWM signal. When duty cycle is zero, LEDs are turned off. For 50% duty cycle, it will result an average
ILED to be half the programmed LED current which is set by RSET.
ISET
The ISET Pin is a voltage input to set the current of LED. An external resistor is used to set the output current, as
approximated with the following equation:
RSET = 460 * (1.2V/ILED)
However, the RSET shall not be selected to exceed the maximum current delivery capability of the device, 25mA.
A PWM signal or analog signal can also be applied at ISET pin to control the LED brightness.
2009/04/20
Ver.2
Page 5
SYNC-POWER [ SYNC POWER CROP. ]
