+10V
a) C
2+
GND
GND
b) C
2–
–10V
Figure 3. Charge Pump Waveforms
pump. Each model within the Series incorpo-
rates variations of these circuits to achieve the
desired configuration and performance.
Transmitter/Driver
The drivers are inverting transmitters, which ac-
cept either TTL or CMOS inputs and output the
RS-232 signals with an inverted sense relative to
the input logic levels. Typically, the RS-232 out-
put voltage swing is
±9V
with no load, and
±5V
minimum with full load. The transmitter outputs
are protected against infinite short–circuits to
ground without degradation in reliability. The
drivers of the
SP200, SP206, SP206B, SP207B,
SP211, SP211B
and
SP213
can be tri–stated by
using
the
SHUTDOWN
function.
In the “power off” state, the output impedance will
remain greater than 300 Ohms, again satisfying the
RS-232 specifications. Should the input of the
V
CC
= +5V
driver be left open, an internal 400kOhm pullup
resistor to V
CC
forces the input high, thus commit-
ting the output to a low state. The slew rate of the
transmitter output is internally limited to a maxi-
mum of 30V/µs in order to meet the 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.
Receivers
The receivers convert RS-232 input signals to
inverted TTL signals. Since the input is usually
from a transmission line where long cable lengths
and system interference can degrade the signal,
the inputs have a typical hysteresis margin of
500mV. This ensures that the receiver is virtu-
ally immune to noisy transmission lines. Should
an input be left unconnected, a 5kOhm pulldown
resistor to ground will commit the output of the
receiver to a high state.
+5V
C
1
+
–
C
4
+
–
+
C
2
+
–
–
V
DD
Storage Capacitor
V
SS
Storage Capacitor
–5V
–5V
C
3
Figure 4. Charge Pump — Phase 3
Date:05/26/2005
+5V High-Speed RS232 Transceivers
© Copyright 2005 Sipex Corporation
7
SIPEX [ SIPEX CORPORATION ]
