S-8821 datasheet(11/19 Pages) SII

11 / 19 page

VOLTAGE REGULATION STEP-UP CHARGE PUMP DC-DC CONVERTER

Rev.3.1_00

S-8821 Series

Seiko Instruments Inc.

External Capacitor Selection

1. Input and Output Capacitors (CIN, COUT)

The input capacitor (CIN) lowers the power supply impedance and averages the input current.

The CIN 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 (COUT), 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 (CPUMP)

The pump capacitor (CPUMP) 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.

S-8821 Datasheet(PDF) 11 Page - Seiko Instruments Inc