SP3221E 데이터 시트보기 (PDF) - Exar Corporation

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SP3221E

Intelligent +3.0V to +5.5V RS-232 Transceiver

Exar Corporation 

Charge Pump Capacitor selection

The Exar charge pump is designed to

operate reliably with a range of low cost

capacitors.Either polarized or non polar-

ized capacitors may be used. If polarized

capacitors are used they should be oriented

as shown in the Typical Operating Circuit.

The V+ capacitor may be connected to either

ground or Vcc (polarity reversed.)

The charge pump operates with 0.1µF ca-

pacitors for 3.3V operation. For other supply

voltages, see the table for required capacitor

values. Do not use values smaller than those

listed. Increasing the capacitor values (e.g.,

by doubling in value) reduces ripple

on the transmitter outputs and may slightly

reduce power consumption. C2, C3, and

C4 can be increased without changing

C1’s value

For best charge pump efficiency locate the

charge pump and bypass capacitors as

close as possible to the IC. Surface mount

capacitors are best for this purpose. Using

capacitors with lower equivalent series re-

sistance (ESR) and self-inductance, along

with minimizing parasitic PCB trace induc-

tance will optimize charge pump operation.

Designers are also advised to consider that

capacitor values may shift over time and

operating temperature.

Minimum recommended charge pump capacitor value

Input Voltage VCC

Charge pump capacitor value

3.0V to 3.6V

C1 - C4 = 0.1µF

4.5V to 5.5V

C1 = 0.047µF, C2-C4 = 0.33µF

3.0V to 5.5V

C1 - C4 = 0.22µF

Table 4. Capacitor selection table

Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • www.exar.com

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SP3221E_200_081816

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