SP3221E Datasheet, PDF (9/20 Pages) Sipex Corporation – Intelligent +3.0V to +5.5V RS-232 Transceiver

Figure 6. Loopback Test Circuit for RS-232 Driver
Data Transmission Rates
Receiver
The receiver converts ±5.0V EIA/TIA-232
levels to TTL or CMOS logic output levels.
The receiver has an inverting output that can
be disabled by using the EN pin.
The receiver is active when the AUTO ON-
LINE® circuitry is enabled or when in shut-
down. During the shutdown, the receiver will
continue to be active. If there is no activity
present at the receiver for a period longer
than 100µs or when SHUTDOWN is enabled,
the device goes into a standby mode where
the circuit draws 1µA. Driving EN to a logic
HIGH forces the output of the receiver into
high-impedance. The truth table logic of the
SP3221E 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.
Figure 7. Loopback Test Circuit result at 250Kbps
(Driver Fully Loaded)
Device: SP3221E
SHUTDOWN EN
0
0
0
1
1
0
1
1
T_XOUT
High Z
High Z
Active
Active
R_XOUT
Active
High Z
Active
High Z
Table 2. SHUTDOWN and EN Truth Tables
Note: In AUTO ON-LINE^® Mode where ONLINE = GND
and SHUTDOWN = V_CC, the device will shut down if
there is no activity present at the Receiver inputs.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com

SP3221E_102_091014