SP3238EEY-L-TR Datasheet, PDF (8/21 Pages) Exar Corporation – Intelligent +3.0V to +5.5V RS-232 Transceiver

VCC
+
C5 0.1µF
VCC
C1+
+
V+
C1 0.1µF
C1-
C2+ SP3238E _V-
+
C2 0.1µF
C2-
LOGIC
INPUTS
TxIN
TxOUT
LOGIC
OUTPUTS
VCC
RxOUT
ONLINE
SHUTDOWN
RxIN
5kΩ
GND
+
C3 0.1µF
C4 0.1µF
+
1000pF
Figure 7. Loopback Test Circuit for RS-232 Driver
Data Transmission Rates
Figure 8. Loopback Test results at 120kbps
(All Drivers Fully Loaded)
Receivers
The receivers convert +5.0V EIA/TIA-232
levels to TTL or CMOS logic output levels. Re-
ceivers are High-Z when the AUTO ON-LINE^®
circuitry is enabled or when in shutdown.
The SP3238E includes an additional non-in-
verting receiver with an output R₁OUT. R₁OUT
is an extra output that remains active and
monitors activity while the other receiver
outputs are forced into high impedance.
This allows a Ring Indicator (RI) signal from a
peripheral to be monitored without forward
biasing the TTL/CMOS inputs of the other
devices connected to the receiver outputs.
Since receiver input is usually from a transmis-
sion 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–patented 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 symmetrical 5.5V
power supplies. The internal power supply
consists of a regulated dual charge pump that
provides output voltages 5.5V regardless of
the input voltage (V_CC) over the +3.0V to +5.5V
range. This is important to maintain compli-
ant RS-232 levels regardless of power supply
fluctuations.
Figure 9. Loopback Test results at 250Kbps
(All Drivers Fully Loaded)
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

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