S-8821 Seiko Instruments, S-8821 Datasheet - Page 8

• Manufacturer Part Number: S-8821
• Description: VOLTAGE REGULATION STEP-UP CHARGE PUMP DC-DC CONVERTER
• Manufacturer: Seiko Instruments

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8
VOLTAGE REGULATION STEP-UP CHARGE PUMP DC-DC CONVERTER
S-8821 Series
Operation
1. Basic operation
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
voltage (V
pulse frequency in order to keep the output voltage constant.
Figure 6 shows the block diagram of the S-8821 Series.
C
PUMP
C
IN
=0.10 μF
=4.7 μF
ref
) are compared by a comparator. This comparator signal is used to modulate the oscillation
VIN
C+
C−
SW2
SW1
SW3
SW4
control
Switch
circuit
Seiko Instruments Inc.
Soft start
circuit
ON/OFF
Figure 6
PFM control
(1.0 MHz)
oscillator
circuit
ON/OFF
circuit
Reference
voltage
+
-
s
R
R
s
f
and R
GND
f
and reference
VOUT
Rev.3.1
C
OUT
=10 μF
_00
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