SP2209EEY datasheet(9/15 Pages) SIPEX

9 / 15 page

SP2209E DS/06

SP2209E High ESD Dual Port RS-232 Transceivers

One receiver in each RS-232 port can be kept

active by a low current, +3.3V to +5V power

supply while the rest of the channels are pow-

ered down. This allows the SP2209E device to

monitor peripheral devices while the rest of the

system is in a power-saving standby mode.

The SP2209E device can be implemented as a

power management device to wake up the entire

system when any communication is initiated in

peripheral devices. The SP2209E device has a

low standby current of 100

µA.

Since receiver input is usually from a transmission

line where long cable lengths and system

interference can degrade the signal, the inputs

have a typical hysteresis margin of 300mV.

This ensures that the receiver is virtually

immune to noisy transmission lines and inputs

with slow transition times.

Charge Pump

The charge pump is a Sipex–patented design

(U.S. 5,306,954) and uses a unique approach

compared to older less–efficient designs.

The charge pump requires two external

capacitors using a two–phase voltage

shifting technique with a 200kHz internal

oscillator to attain a -9V power supply. Refer to

Figure 7 for the internal charge pump circuit.

The internal power supply consists of a charge

pump that provides output voltages of at least

+5V regardless of the input voltage (V

DD). This

is important to maintain compliant RS-232

levels regardless of power supply fluctuations.

A description of each phase follows.

C2-

VDD

VC2- = -VDD

Figure 7. Charge Pump Circuit

Figure 8. Charge Pump Waveforms

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