SP211EEA-L-TR Datasheet, PDF (6/15 Pages) Exar Corporation – 5V RS-232 Serial Transceivers

+10V
a) C2+
GND
GND
b) C2+
-10V
Figure 1. Charge Pump Waveforms
Transmitter/Driver
The drivers are inverting transmitters, which ac-
cept either TTL or CMOS inputs and output the
RS-232 output signals with an inverted sense
relative to the input logic levels. Typically, the
RS-232 output voltage swing is +/-9V with no
load, and +/-5V minimum with full load. The
transmitter outputs are protected against infi-
nite short-circuits to ground without degrada-
tion in reliability. The drivers of the SP206 and
SP211 can be tri-stated by using the SHUT-
DOWN function.
In the "power off" state, the output impedance
will remain greater than 300 Ohms, again satis-
fying the RS-232 specifications. Should the input
of the driver be left open, an internal 400kOhm
pull-up resistor to Vcc forces the input high, thus
committing the output to a low state. The slew
rate of the transmitter output is internally limited
to a maximum of 30V/µs in order to meet he EIA
standards (EIA RS-232D 2,1,7, Paragraph 5).
The transition of the loaded output from high to
low also meets the monotonicity requirements
of the standard.
DESCRIPTION
Receivers
The receivers convert RS-232 input signals to
inverted TTL signals. Since the input is usu-
ally from a transmission line where long cable
length and system interference can degrade
the signal, the inputs have a typical hysteresis
margin of 500mV. This ensures that the re-
ceiver is virtually immune to noisy transmission
lines. Should an input be left unconnected, an
internal 5kohm pull-down resistor to ground will
commit the output of the receiver to a HIGH
state.
Shutdown Mode
The SP206 and SP211 feature a control input
(SD) which will disable the device and reduce
the power supply current to less than 10µA,
making the parts ideal for battery-powered sys-
tems. In the "shutdown" mode the receivers
and transmitters will both be tri-stated. The V+
output of the charge pump will discharge to Vcc
and the V- output will discharge to ground.
Enable (EN)
The SP206 and SP211 feature an enable input
which allows the receiver outputs to be either
tri-stated or enabled. This can be especially
useful when the receiver is tied directly to a
microprocessor data bus. The enable pin is
active high.
V_CC = +5V
+
C_{1 –}
–5V
+5V
+
C_{2 –}
–5V
C₄
+ – _{VDD Storage Capacitor}
–+
C₃
V_SS Storage Capacitor
Figure 2, Charge pump - Phase 1
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • Fax [phone] • www.exar.com SP206, 207, 208, 211_101_060111