SP3223ECY-L Datasheet, PDF (10/20 Pages) Exar Corporation – Intelligent 3.0V to 5.5V RS-232 Transceivers

Device: SP3223
SHUTDOWN EN
0
0
0
1
1
0
T_XOUT
High Z
High Z
Active
1
1
Active
R_XOUT
Active
High Z
Active
High Z
Table 3. 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.
Receivers
The receivers convert ±5.0V EIA/TIA-232
levels to TTL or CMOS logic output levels.
Receivers have an inverting output that can
be disabled by using the EN pin.
Receivers are active when the AUTO ON-
LINE® circuitry is enabled or when in shut-
down. During the shutdown, the receivers will
continue to be active. If there is no activity
present at the receivers 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 outputs of the receivers into
high-impedance. The truth table logic of the
SP3223 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 14. Loopback Test Circuit for RS-232 Driver
Data Transmission Rates
Figure 15. Loopback Test Circuit result at 250Kbps
(All Drivers Fully Loaded)
Charge Pump
The charge pump 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 symmetrical
5.5V power supplies. The internal power
supply consists of a regulated dual charge
pump that provides output voltages of
+/-5.5V regardless of input voltage (V_CC)
over the +3.0V to +5.5V range. This
is important to maintain compliant RS-
232 levels regardless of power supply
fluctuations.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com
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SP3223E/EB/EU_101_062712