Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-707 • www.exar.com

SP3223E/EB/EU_0_06272

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Receivers

The receivers convert ±5.0V EIA/TIA-232

levels to TTL or CMOS logic output levels.

Receivers have an inverting output that can

be disabled by using the EN pin.

Receivers are active when the AUTO ON-

LINE® circuitry is enabled or when in shut-

down.Duringtheshutdown,thereceiverswill

continue to be active. If there is no activity

present at the receivers for a period longer

than00µsorwhenSHUTDOWNisenabled,

the device goes into a standby mode where

the circuit draws µA. Driving EN to a logic

HIGH forces the outputs of the receivers into

high-impedance. The truth table logic of the

SP3223 driver and receiver outputs can be

found in Table 2.

Since receiver input is usually from a trans-

mission 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. Should an input be left unconnected,

an internal 5kΩ pull-down resistor to ground

will commit the output of the receiver to a

HIGH state.

Table 3. SHUTDOWN and EN Truth Tables

and SHUTDOWN = V

there is no activity present at the Receiver inputs.

Figure 4. Loopback Test Circuit for RS-232 Driver

Data Transmission Rates

Charge Pump

The charge pump uses a unique approach

compared to older less–efficient designs.

The charge pump still requires four external

capacitors, but uses a four–phase voltage

shifting technique to attain symmetrical

5.5V power supplies. The internal power

supply consists of a regulated dual charge

pump that provides output voltages of

+/-5.5V regardless of input voltage (V

over the +3.0V to +5.5V range. This

is important to maintain compliant RS-

232 levels regardless of power supply

fluctuations.

Figure 5. Loopback Test Circuit result at 250Kbps

(All Drivers Fully Loaded)

Device: SP3223

SHUTDOWN

EN

T

R

0

0

High Z

Active

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High Z

High Z



0

Active

Active





Active

High Z