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

SP3222EB/SP3232EB_103_081414

9

Receivers

The Receivers convert EIA/TIA-232 levels

to TTL or CMOS logic output levels. The

SP3222EB 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

of the SP3222EB 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 pulldown resistor to ground

will commit the output of the receiver to a

HIGH state.

Table 2. SP3222EB Truth Table Logic for Shutdown

and Enable Control

Figure 10. SP3222EB/SP3232EB Driver Loopback

Test Circuit

Charge Pump

The charge pump is an Exar-patended

design (U.S. 5,306,954) and 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 sym-

metrical 5.5V power supplies. The internal

power supply consists of a regulated dual

charge pump that provides output voltages

of +/-5.5V regardless of the input voltage

(Vcc) over the +3.0V to +5.5V range.

Figure 12. Loopback Test results at 250kbps

Figure 11. Loopback Test results at 120kbps

SP3222EB

SP3232EB

GND

TxIN

TxOUT

C1+

C1-

C2+

C2-

V+

V-

0.1µF

0.1µF

0.1µF

+

C2

C5

C1

+

+

C3

C4

+

+

0.1µF

0.1µF

LOGIC

INPUTS

5kΩ

RxIN

RxOUT

LOGIC

OUTPUTS

EN*

*SHDN

1000pF

* SP3222EB only

SHDN

EN

TxOUT

RxOUT

0

0

Tri-state

Active

0

1

Tri-state

Tri-state

1

0

Active

Active

1

1

Active

Tri-state

DESCRIPTION