S-8821 Datasheet, PDF (8/19 Pages) Seiko Instruments Inc – VOLTAGE REGULATION STEP-UP CHARGE PUMP DC-DC CONVERTER

VOLTAGE REGULATION STEP-UP CHARGE PUMP DC-DC CONVERTER
S-8821 Series
Rev.3.1_00
„ Operation
1. Basic operation
Figure 6 shows the block diagram of the S-8821 Series.
The S-8821 series controls the output voltage 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 circuit, and operates the step-up charge pump.
The output voltage is fed 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.
VIN
C_IN=4.7 μF
SW1
C+
C_PUMP=0.10 μF
C−
SW2
SW3
SW4
Switch
control
circuit
Soft start
circuit
PFM control
oscillator
circuit
(1.0 MHz)
R_s
+
R_f
-
ON/OFF
circuit
Reference
voltage
VOUT
C_OUT=10 μF
ON/OFF
GND
Figure 6
8
Seiko Instruments Inc.