SP3222EU Datasheet, PDF (9/20 Pages) Sipex Corporation – 3.3V, 1000 Kbps RS-232 Transceivers

VCC
+
C5 0.1µF
+
C1 0.1µF
+
C2 0.1µF
LOGIC
INPUTS
VCC
C1+
V+
C1-
C2+ ^SP3222EU V-
SP3232EU
C2-
TxIN
TxOUT
+
C3 0.1µF
C4 0.1µF
+
LOGIC
OUTPUTS
RxOUT
EN*
RxIN
5kΩ
*SHDN
VCC
GND
250pF or 1000pF
* SP3222EU only
Figure 11. SP3222EU/SP3232EU Driver Loopback
Test Circuit
Figure 12. Loopback Test results at 250kbps
DESCRIPTION
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.
SHDN
EN
TxOUT
RxOUT
0
0
Tri-state
Active
0
1
Tri-state
Tri-state
1
0
Active
Active
1
1
Active
Tri-state
Table 2. SP3222EU Truth Table Logic for Shutdown
and Enable Control
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.
Figure 13. Loopback Test results at 1000kbps
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3222EU/SP3232EU_102_031413