S-8813 Datasheet, PDF (10/29 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
2. Step-up Charge Pump
The step-up charge pump steps up the voltage by switching ON/OFF the SW1 to SW4 switching
transistors.
First, in order to charge the pump capacitance (C_PUMP), set SW1 to OFF, SW2 to ON, SW3 to OFF, and
SW4 to ON (charge cycle). Following charging the electricity, in order to discharge the charged electricity
to the output capacitance (C_OUT), SW1 set the switches as to ON, SW2 to OFF, SW3 to ON, and SW4 to
OFF (discharge cycle).
The input voltage can be stepped up to a constant voltage value by repeating this charge cycle and
discharge cycle.
In the S-8813 Series, the V_IN voltage range of 2.7 V to 4.5 V is stepped up to V_CPOUT = 5 V.
SW2: ON
SW1: OFF
V_IN
Current flow
C_PUMP=0.22 μF
C_OUT=10 μF
SW4: ON
SW3: OFF
Figure 6 Charge Cycle
SW2: OFF
SW1: ON
V_IN
Current flow
C_PUMP=0.22 μF
SW4: OFF
SW3: ON
C_OUT=10 μF
Figure 7 Discharge Cycle
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Seiko Instruments Inc.