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SP3238EEA-L Datasheet, PDF (8/20 Pages) Exar Corporation – Intelligent 3.0V to 5.5V RS-232 Transceiver | |||
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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
5kâ¦
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 5k⦠pulldown resistor
to ground will commit the output of the receiver
to a HIGH state.
Charge Pump
The charge pump is an Exarâpatented design
(U.S. 5,306,954) and uses a unique approach
compared to older lessâefficient designs.
The charge pump still requires four external
capacitors, but uses a fourâphase 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 (VCC) 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
SP3238E_100_020111
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