SP232A
Enhanced RS-232 Line Drivers/Receivers
FEATURES
• Operates from a Single +5V Power Supply
• Meets all RS-232F and ITU V.28 Specifications
• Operates with 0.μF Ceramic Capacitors
• High Data rate - 20kbps under load
• Low power CMOS Operation
• +/-2kV Human Body Model ESD Protection
• Lead Free packaging available
The SP232A is a line driver and receiver pair that meets the specifications of RS-232 and V.28 serial
protocols. This device is pin-to-pin compatible with popular industry standard pinouts. The SP232A
offers 20kbps data rate under load, small ceramic type 0.μF charge pump capacitors and overall
ruggedness for comercial applications. The SP232A features Exar's BiCMOS design allowing for low
power operation without sacrificing performance. This device is avaialble in plastic DIP, SOICW and
nSOIC packages operating over the commercial and industrial temperature ranges.
DESCRIPTION
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • Fax (50)668-707 • www.exar.com
SP232A_00_05308
These are stress ratings only and functional opera-
tion of the device at these ratings or any other above
those indicated in the operation sections of the speci-
fications below are not implied. Exposure to absolute
maximum ratings conditions for extended periods of
time may affect reliability.
Supply Voltage (V
CC
)...............................................+ 6V
V+........................................................................... (Vcc-0.3V) to +.0V
V- .............................................................................-.0V
Input Voltages
Tin.....................................................-0.3V to (Vcc + 0.3V)
Rin............................................................................+/-5V
Output Voltages
Tout...............................................(V+, +0.3V) to (V-, -0.3V
Rout...................................................-0.3V to (Vcc + 0.3V)
AbSoLUTE MAxiMUM RATingS
Short Circuit duration
Tout.....................................................Continuous
Package Power Dissipation:
Plastic DIP...............................................375mW
(derate 7mW/°C above +70°C)
Small Outline...........................................375mW
(derate 7mW/°C above +70°C)
Storage Temperature..................-65°C to +50°C
Lead Temperature (soldering, 0s).......... +300°C
Vcc=5V ±0%, 0.
μ
F charge pump capacitors, T
min
to T
max
,
unless otherwise noted, Typical values are Vcc=5V
and T
a
=25°C
PARAMETER
TTL inPUT
Logic Threshold LOW
Logic Threshold HIGH
Logic Pull-Up Current
TTL oUTPUT
Output Voltge LOW
Output Voltage HIGH
RS-232 oUTPUT
output
Voltage Swing
Output Resistance
Output Short Circuit Current
Maximum Data Rate
RS-232 inPUT
Voltage Range
Voltage Threshold LOW
Voltage Threshold HIGH
Hysteresis
Resistance
Vcc = 5V,
T
a
=25°C
Vcc = 5V,
T
a
=25°C
Vcc = 5V,
T
a
=25°C
0.2
3
-5
0.8
.2
.7
0.5
5
2.4
.0
7
+5
Volts
Volts
Volts
Volts
kΩ
all
Transmitter outputs loaded
with 3k ohms to GND
Vcc = 0V, Vout = +/-2V
Infinite Duration
CL = 2500pF, RL = 3kΩ
20
+/-5.0
300
+/-8
240
+/-6.5V
Volts
Ohms
mA
kbps
i
ouT
= 3.2
mA:
V
cc
= +5V
i
ouT
= -1.0
mA
3.5
0.4
Volts
Volts
Tin
Tin
Tin = 0V
2.0
5
200
0.8
Volts
Volts
μA
TEST ConDiTionS
Min
TYP
MAx
UniT
ELECTRiCAL CHARACTERiSTiCS
T
a
=25°C,
-15V ≤ V
in
≤ +15V
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • Fax (50)668-707 • www.exar.com
SP232A_00_05308
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Vcc=5V ±0%, 0.
μ
F charge pump capacitors, T
min
to T
max
,
unless otherwise noted, Typical values are Vcc=5V
and T
a
=25°C
DYnAMiC CHARACTERiSTiCS
Driver Propagation Delay
Receiver Propagation Delay
Instantaneous Slew Rate
TTL to RS_232; CL = 50pF
RS-232 to TTL,
CL = 10pF, RL = 3-7kΩ
CL = 2500pF, RL = 3kΩ;
Measured from +3V to -3V or
-3V to +3V
.5
0.
3.0
.0
30
μs
μs
V/ μs
V/ μs
ELECTRiCAL CHARACTERiSTiCS
Transition Region Slew Rate
0
PoWER REQUiREMEnTS
Vcc Power Supply Current
Vcc Power Supply Current, Loaded
No Load, Vcc = 5V, T
a
=25°C
All Transmitters RL = 3kΩ,
T
a
=25°C
.5
5
mA
mA
Pin ASSignMEnTS
Pin number Pin name
2
3
4
5
6
7
8
C+
V+
C-
C2+
C2-
V-
T2OUT
R2IN
R2OUT
T2IN
TIN
ROUT
RIN
TOUT
GND
Vcc
Pin Function
Positive terminal of the voltage doubler charge pump
capacitor
+6.5V generated by the charge pump
Negative terminal of the voltage doubler charge pump
capacitor
Positive terminal of the inverting charge pump capacitor
Negative terminal of the inverting charge pump capacitor
-6.7V generated by the charge pump
RS-232 driver output
RS-232 receiver input
TTL/CMOS receiver output
TTL/CMOS driver input
TTL/CMOS driver input
TTL/CMOS receiver output
RS-232 receiver input
RS-232 driver output
Ground
5V supply voltage
9
0
2
3
4
5
6
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • Fax (50)668-707 • www.exar.com
SP232A_00_05308
3
DESCRiPTion
DETAiLED DESCRiPTion
The SP232A transceiver is a two driver and two
receiver device that meets the EIA/TIA- 232 and
V.28 serial communication protocol. The device
is pin-to-pin compatible with popular industry
standard pinouts. The SP232A offers 20kbps
data rate, 0V/
μ
s slew rate and a regulated
charge pump that operates from a single 5V
supply. The proprietary on-board charge pump
generates a regulated output of +/-6.5V for RS-
232 compliant voltage levels.
Theory of operation
The SP232A is made up of three basic circuit
blocks: . Driver, 2. Receiver, and 3. charge
pump.
Drivers
The drivers are inverting level transmitters that
convert TTL or CMOS logic levels to EIA/TIA-
232 levels with an inverted sense relative to the
input logic levels. Typically, the RS-232 output
voltage swing is +/-6.5V with no load and +/-
5.0V minimum when fully loaded. The driver out-
puts are protected against infinite short-circuits
to ground without degradation in reliability.
The drivers can guarantee output data rates of
20Kbps under worst case loading of 3k ohms
and 2500pF.
The driver output Slew Rate is internally limited
to 30V/μs in order to meet the EIA standards
(EIA-232F). Additionally, the driver output LOW
to HIGH transition meet the monotonicity output
requirements of the standard.
Receivers
The receivers convert EIA/TIA-232 signal levels
to TTL or CMOS logic output levels. Since the
input is usually from a transmission line, where
long cable length and system interference can
degrade the signal, the receiver inputs have a
typical hysteresis margin of 500mV. This en-
sures that the receiver is virtually immune to
noisy transmission lines. Should a input be left
unconnected, an internal 5Kohm pull-down re-
sistor to ground will commit the output of the re-
ceiver to a logic HIGH state. The input voltage
range for the SP232A Receiver is +/-5V.
Charge pump
The charge pump is a patented design and
uses a unique approach compared to older less
efficient designs. The charge pump requires 4
external capacitors and uses a four phase volt-
age shifting technique. The internal power sup-
ply consists of a regulated dual charge pump
that provides output voltages of +/-6.5V. This
is important to maintain compliant RS-232 lev-
els regardless of power supply fluctuations.
The charge pump operates in a discontinous
mode using an internal oscillator. If the voltages
are less than a magnitude of 6.5V, the charge
pump is enabled. If the output voltage exceed
a magnitude of 6.5V then the charge pump is
disabled. The internal oscillator controls the four
phases of the voltage shifting. A description of
each phase follows:
Phase 1
Vss charge store and double: The positive ter-
minals of capacitors C and C2 are charged
from Vcc with their negative terminals initially
connected to ground. C+ is then connected
to ground and the stored charge from C- is
superimposed onto C2-. Since C2+ is still con-
nected to Vcc the voltage potential across C2 is
now 2 x Vcc.
Phase 2
Vss transfer and invert: Phase two connects
the negative terminal of C2 to the Vss storage
capacitor and the positive terminal of C2 to
ground. This transfers the doubled and inverted
(V-) voltage onto C4. Meanwhile, capacitor C
is charged from Vcc in order to prepare it for its
next phase.
Phase 3
Vdd charge store and double: Phase three is
identical to the first phase. The positive termi-
nals of C and C2 are charged from Vcc with
their negative terminals initially connected to
ground. C+ is then connected to ground and
the stored charge from C- is superimposed
onto C2-. Since C2+ is still connected to Vcc
the voltage potential across capacitor C2 is now
2 x Vcc.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • Fax (50)668-707 • www.exar.com
SP232A_00_05308
4
Phase 4
Vdd transfer. The fourth phase connects the
negative terminal of C2 to ground and the posi-
tive terminal of C2 to the Vdd storage capacitor .
This transfers the doubled (V+) voltage onto C3.
Meanwhile, capacitor C is charged from Vcc to
prepare it for its next phase.
Under lightly loaded conditions, the intelligent
pump oscillator maximizes efficiency by running
only as needed to maintain V+ and V- voltage
levels. Since interface transceivers spend most
of their time at idle, this power-efficient innova-
tion can greatly reduce total power consump-
tion. This improvement is made possible by
the independent phase sequences of the Exar
charge pump design.
DESCRiPTion
The clock rate of the charge pump typically op-
erates greater than 70kHz allowing the pump to
operate efficiently with small 0.1uF capacitors.
Efficient operation depends on rapid charging
and discharging of C and C2. Therefore, the
capacitors should be mounted as close as pos-
sible to the IC and have a low ESR (equivalent
series resistance). Inexpensive, surface mount
ceramic capacitors are ideal for use on charge
pump. If polarized capacitors are used the posi-
tive and negative terminals should be connect-
ed as shown on the typical operating circuit. A
diagram of the 4 individual phases is shown in
Figure .
+
V
CC
-
Phase 2 – Vss transfer from C2 to C4.
Meanwhile C1 is charged to Vcc
+
+
V
CC
-
C
Phases 1 and 3: Store/Double.
Double charge from C1 onto C2.
C2 is now charged to -2xVcc
+
1
C
+
2
V+
e
-
e
-
C
+
3
e
-
C
Vss
4
+
C
+
1
C
+
2
V+
V-
C
+
3
Patented 5,306,954
+
V
CC
-
e
-
e
-
C
4
Phase 4 V
DD
transfer from C2 to C3.
Meanwhile C1 is charged to Vcc
V
e
+
DD
e
+
+
C
+
1
C
+
2
V+
V-
C
+
3
e
-
C
4
Figure . Charge pump phases
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • Fax (50)668-707 • www.exar.com
SP232A_00_05308
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