SP3224E datasheet(13/23 Pages) SIPEX

13 / 23 page

Rev P 11/20/06

SP3224E-SP3227E Transceivers with Auto On-line® Plus

THEORY OF OPERATION

The SP3224E-SP3227E devices have the

advanced Auto On-Line® Plus feature

RS-232 signals use both positive and neg-

ative voltages of greater than ±5V magni-

tude. Receivers have nominal 5kΩ imped-

ance to ground. Even when idle, drivers

will maintain output signal voltage creating

a continuous current ﬂow. In low power,

battery operated devices this constant cur-

rent drain can decrease battery life

signiﬁcantly.

are widely used for power-supply decou-

pling) are ideal for use on the charge pump.

The charge pumps are designed to be able

to function properly with a wide range of

capacitor styles and values. If polarized ca-

pacitors are used the positive and negative

terminals should be connected as shown

on the Typical Operating Circuit.

Capacitance values may be increased if

operating at higher VCC or to provide great-

er stability as the capacitors age.

Minimum Recommended Charge Pump Capacitor Values

Input Voltage VCC

Charge Pump Capacitor Value for SP32XX

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

Charge Pump Capacitor Values

Phases 1 and 3: Store/Double.

Double charge from C1 onto C2.

C2 is now charged to -2xVcc

Phase 2 – Vss transfer from C2 to C4.

Meanwhile C1 is charged to Vcc

Vss

transfer from C2 to C3.

Meanwhile C1 is charged to Vcc

V-

V+

V-

V+

Patented 5,306,954 (Sipex, inc.)

Phase 4 VDD

Charge Pump Phases

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