S-8813 Datasheet, PDF (8/29 Pages) Seiko Instruments Inc – 3-CHANNEL WHITE LED DRIVER IC (CHARGE PUMP IC WITH BUILT-IN CONSTANT-CURRENT CIRCUIT)

3-CHANNEL WHITE LED DRIVER IC (CHARGE PUMP IC WITH BUILT-IN CONSTANT-CURRENT CIRCUIT)
S-8813 Series
Rev.2.1_00
 Operation
1. Basic Operation
The S-8813 series controls by using the pulse frequency modulation (PFM) method. The SW1 to SW4
switching transistors are switched ON/OFF with the clock generated by the internal oscillator (OSC), and
operates the step-up charge pump.
The output voltage is feed back and the voltage split by feedback resistances R_s and R_f and reference
voltage (V_ref) are compared by a comparator. This comparator signal is used to modulate the oscillation
pulse frequency in order to keep the output voltage constant.
Using this constant output voltage as the voltage source, a constant current is created using V_ref and the
external resistance value applied to the RISET pin, and this constant current is supplied as the current
output to the three channels of output pins (IOUT1 to IOUT3). Therefore, even if the white LED V_F
(forward voltage) varies between 3 V and 4 V, a constant current can be supplied, making it possible to
reduce fluctuations in brightness and keep white LEDs shining at a constant brightness.
8
Seiko Instruments Inc.