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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3222EU/SP3232EU_102_031413

The

SP3222EU/SP3232EU transceivers

meet the EIA/TIA-232 and ITU-T V.28/V.24

communication protocols and can be imple-

mented in battery-powered, portable, or

hand-held applications such as notebook

or palmtop computers. The

SP3222EU/

SP3232EU devices feature Exar's propri-

etary on-board charge pump circuitry that

generates ±5.5V for RS-232 voltage levels

from a single +3.0V to +5.5V power supply.

This series is ideal for +3.3V-only systems,

mixed +3.3V to +5.5V systems, or +5.0V-

only systems that require true RS-232

performance. The

SP3222EU/SP3232EU

devices can operate at a minimum data rate

of 1000kbps.

The

SP3222EU and SP3232EU are 2-

driver/2- receiver devices ideal for portable

or hand-held applications. The

SP3222EU

features a 1µA shutdown mode that reduces

power consumption and extends battery life

in portable systems. Its receivers remain

active in shutdown mode, allowing external

devices such as modems to be monitored

using only 1µA supply current.

THEORY OF OPERATION

The

SP3222EU/SP3232EU series is made

up of three basic circuit blocks:

1. Drivers

2. Receivers

3. The Exar proprietary charge pump

Drivers

The drivers are inverting level transmitters

that convert TTL or CMOS logic levels to

+5.0V EIA/TIA-232 levels with an inverted

sense relative to the input logic levels.

Typically, the RS-232 output voltage swing

is +5.4V with no load and +5V minimum fully

loaded. The driver outputs are protected

against infinite short-circuits to ground with-

out degradation in reliability. Driver outputs

will meet EIA/TIA-562 levels of +/-3.7V with

supply voltages as low as 2.7V.

The drivers have a minimum data rate of

1000kbps fully loaded with 3kΩ in parallel

with 250pF, ensuring compatability with PC-

to-PC communication software.

Figure 11 shows a loopback test circuit

used to test the RS-232 Drivers. Figure

12 shows the test results of the loopback

circuit with all drivers active at 250kbps

with RS-232 loads in parallel with a

1000pF capacitor. Figure 13 shows the

test results where one driver was active

at 1000kbps and all drivers loaded with an

RS-232 receiver in parallel with 250pF

capacitors.

The

SP3222EU driver's output stages are

turned off (tri-state) when the device is in

shutdown mode. When the power is off, the

SP3222EU device permits the outputs to be

driven up to +/-12V. The driver's inputs do

not have pull-up resistors. Designers should

connect unused inputs to Vcc or GND.

In the shutdown mode, the supply current

falls to less than 1µA, where SHDN = LOW.

When the

SP3222EU device is shut down,

the device's driver outputs are disabled (tri-

stated) and the charge pumps are turned off

with V+ pulled down to Vcc and V- pulled to

GND. The time required to exit shutdown is

typically 100µs. Connect SHDN to Vcc if the

shutdown mode is not used.

Receivers

The Receivers convert EIA/TIA-232 levels

to TTL or CMOS logic output levels. The

SP3222EU receivers have an inverting

tri-state output. These receiver outputs

(RxOUT) are tri-stated when the enable

control EN = HIGH. In the shutdown mode,

the receivers can be active or inactive. EN

has no effect on TxOUT. The truth table logic

ofthe

SP3222EUdriverandreceiveroutputs

can be found in Table 2.

DESCRIPTION