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

SP3222EU/SP3232EU_102_031413

9

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.

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.

In most circumstances, decoupling the

power supply can be achieved adequately

using a 0.1µF bypass capacitor at C5 (refer

to figures 9 and 10). In applications that are

sensitive to power-supply noise, decouple

Vcc to ground with a capacitor of the same

value as charge-pump capacitor C1. Physi-

cally connect bypass capcitors as close to

the IC as possible.

Table 2. SP3222EU Truth Table Logic for Shutdown

and Enable Control

Figure 11. SP3222EU/SP3232EU Driver Loopback

Test Circuit

Figure 13. Loopback Test results at 1000kbps

Figure 12. Loopback Test results at 250kbps

SP3222EU

SP3232EU

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

250pF or 1000pF

* SP3222EU 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