VOLTAGE REGULATION STEP-UP CHARGE PUMP DC-DC CONVERTER
S-8821 Series
Rev.5.0_00
Seiko Instruments Inc. 12
External Capacitor Selection
1. Input and Output Capacitors (C
IN
, C
OUT
)
The input capacitor (C
IN
) lowers the power supply impedance and averages the input current.
The C
IN
value is selected according to the impedance of the power supply that is used. Select a ceramic
capacitor with a small equivalent series resistance (ESR). Although this figure varies according to the
impedance of the power supply that is used as well as the load current value, it is generally in the range
of 4.7 μF to 10 μF.
For the output capacitor (C
OUT
), select a ceramic capacitor with a small ESR for smoothing the ripple
voltage. A value of 10 μF is recommended for the capacitance value. Use of a capacitor with a
capacitance lower than 10 μF results in a larger ripple voltage. Conversely, use of a capacitor with a
capacitance greater than 10 μF results in the output voltage not being able to rise up to setting value
and the impossibility to obtain the desired output current.
2. Pump Capacitor (C
PUMP
)
The pump capacitor (C
PUMP
) is required for stepping up the voltage. Select a ceramic capacitor with a
small ESR. A capacitance value of 0.10 μF is recommended. Use of a capacitor with a capacitance
greater than 0.10 μF results in a larger ripple voltage. Conversely, use of a capacitor with a capacitance
lower than 0.10 μF results in the output voltage not being able to raise up to setting value and the
impossibility to obtain the desired output current.
