SP3232EBEY-L-TR Datasheet, PDF (9/24 Pages) Exar Corporation – True +3.0V to +5.5V RS-232 Transceivers

Figure 10. SP3222EB/SP3232EB Driver Loopback
Test Circuit
Figure 11. Loopback Test results at 120kbps
DESCRIPTION
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.
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. SP3222EB Truth Table Logic for Shutdown
and Enable Control
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.
Figure 12. Loopback Test results at 250kbps
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7000• www.exar.com
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SP3222EB/SP3232EB_106_022316