SP3232EHCT-L Exar Corporation, SP3232EHCT-L Datasheet - Page 8

• Manufacturer Part Number: SP3232EHCT-L
• Description: 3.3V, 460Kbps RS-232 Transceivers
• Manufacturer: Exar Corporation
• Type: Transceiverr

Specifications of SP3232EHCT-L

• Number Of Drivers/receivers: 2/2
• Protocol: RS232
• Voltage - Supply: 3 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The SP3232EH is a 2-driver / 2-receiver
devices
applications. The SP3232EH transceiver
meets the EIA/TIA-232 and ITU-T V.28/V.24
communication protocols and can be imple-
mented in battery-powered, portable, or
hand-held applications such as notebook or
palmtop computers. The SP3232EH device
features Exar's proprietary on-board charge
pump circuitry that generates ±5.5V for RS-
232 voltage levels from a single +3.0V to
+5.5V power supply. This device is ideal for
+3.3V-only systems, mixed +3.3V to +5.5V
systems, or +5.0V-only systems that require
true RS-232 performance. The SP3232EH
device can operate at a minimum data rate
of 460kbps when fully loaded.
THEORY OF OPERATION
The SP3232EH is made up of three basic
circuit blocks:
1. Drivers
2. Receivers
3. The Exar proprietary charge pump
Drivers
The drivers are inverting level transmitters
that convert TTL or CMOS logic levels to
+5.0V EIA/TIA-232 levels with an inverted
sense relative to the input logic levels.
Typically, the RS-232 output voltage swing
is +5.4V with no load and +5V minimum fully
loaded. The driver outputs are protected
against infinite short-circuits to ground with-
out degradation in reliability. Driver outputs
will meet EIA/TIA-562 levels of +/-3.7V with
supply voltages as low as 2.7V.
The drivers have a minimum data rate of
460kbps fully loaded with 3kΩ in parallel
with 1000pF, ensuring compatibility with
PC-to-PC communication software.
Figure 6 shows a loopback test circuit
used to test the RS-232 Drivers. Figure
7 shows the test results of the loopback
ideal for portable or hand-held
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
8
circuit with all drivers active at 120kbps
with RS-232 loads in parallel with a
1000pF capacitor. Figure 8 shows the
test results where one driver was active
at 460kbps and all drivers loaded with an
RS-232 receiver in parallel with 1000pF
capacitor. Designers should connect unused
inputs to Vcc or GND.
Receivers
The Receivers convert EIA/TIA-232 levels
to TTL or CMOS logic output levels. Since
receiver 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
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-patended
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 sym-
metrical 5.5V power supplies. The internal
power supply consists of a regulated dual
charge pump that provides output voltages
of +/-5.5V regardless of the input voltage
(Vcc) over the +3.0V to +5.5V range.
In most circumstances, decoupling the
power supply can be achieved adequately
using a 0.1µF bypass capacitor at C5 (refer
to figure 5)
In applications that are sensitive to power-
supply noise, decouple Vcc to ground with a
capacitor of the same value as charge-pump
capacitor C1. Physically connect bypass
capacitors as close to the IC as possible.
The charge pump operates in a discontinu-
ous mode using an internal oscillator. If the
output voltages are less than a magnitude
SP3232EH_100_010611
DESCRIPTION