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DS232A
Dual RS-232 Transmitter/Receiver
www.maxim-ic.com
FEATURES
Compatible with LT1181A and MAX232A
High data rate - 250 kbits/sec under load
16-pin DIP or SOIC package
20-pin TSSOP package for height restricted
applications
Operate from single +5V power
Meets all EIA-232E and V.28 specifications
Uses small capacitors: 0.1
μF
Optional industrial temperature range
available (-40°C to +85°C)
PIN ASSIGNMENT
C1+
V+
C1-
C2+
C2-
V-
T2
OUT
R2
IN
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
CC
GND
T1
OUT
R1
IN
R1
OUT
T1
IN
T2
IN
R2
OUT
16-Pin DIP AND SOIC
C1+
V+
C1-
C2+
NC
C2-
V-
NC
T2
OUT
R2
IN
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
NC
V
CC
GND
T1
OUT
R1
IN
R1
OUT
NC
T1
IN
T2
IN
R2
OUT
ORDERING INFORMATION
DS232A
DS232A-N
DS232AR
DS232AR-N
DS232AS
DS232AS-N
DS232AE
DS232AE-N
16-pin DIP
16-pin DIP (Industrial)
16-pin SOIC (150-Mil)
16-pin SOIC (150-Mil) (Industrial)
16-pin SOIC (300-Mil)
16-pin SOIC (300-Mil) (Industrial)
20-pin TSSOP
20-pin TSSOP (Industrial)
20-Pin TSSOP
PIN DESCRIPTION
V
CC
GND
V+
V-
T1
IN
, T2
IN
T1
OUT
, T2
OUT
R1
IN
, R2
IN
R1
OUT
, R2
OUT
C1+, C1-
C2+, C2-
- +5-Volt Supply
- Ground
- Positive Supply Output
- Negative Supply Output
- RS-232 Driver Inputs
- RS-232 Driver Outputs
- Receiver Inputs
- Receiver Outputs
- Capacitor 1 Connections
- Capacitor 2 Connections
DESCRIPTION
The DS232A is a dual RS-232 driver/receiver pair that generates RS-232 voltage levels from a single +5-
volt power supply. Additional
±12-volt
supplies are not needed since the DS232A uses on-board charge
pumps to convert the +5-volt supply to
±10
volts. The DS232A is fully compliant with EIA RS-232E and
V.28/V.24 standards. The DS232A contains two drivers and two receivers. Driver slew rates and data
rates are guaranteed up to 250k bits/sec. The DS232A operates with only 0.1
μF
charge pump capacitors.
OPERATION
The diagram in Figure 1 shows the main elements of the DS232A. The following paragraphs describe the
function of each pin.
1 of 10
112099
DS232A
FUNCTIONAL DIAGRAM OF DS232A
Figure 1
NOTE: C5 is a recommended decoupling capacitor which is the same value as C1, C2, C3, and C4.
( ) Are for TSSOP package only.
PIN DESCRIPTIONS
V
CC
, GND:
DC power is provided to the device on these pins. V
CC
is the +5-volt input.
V+:
Positive supply output (RS-232). V+ requires an external storage charge capacitor of at least 0.1
μF.
A larger capacitor (up to 10
μF)
can be used to reduce supply ripple.
V-:
Negative supply output (RS-232). V- requires an external storage capacitor of at least 0.1
μF.
A
larger capacitor (up to 10
μF)
can be used to reduce supply ripple.
T1
IN
, T2
IN
:
Standard TTL/CMOS inputs for the RS-232 drivers. The inputs of unused drivers can be left
unconnected since each input has a 400 kΩ pullup resistor.
T1
OUT
, T2
OUT
:
Driver outputs at RS-232 levels. Driver output swing meets RS-232 levels for loads up to
3 kΩ. These driver outputs provide current necessary to meet RS-232 levels for loads up to 2500 pF.
2 of 10
DS232A
R1
IN
, R2
IN
:
Receiver inputs. These inputs accept RS-232 level signals (±25 volts) into a protected 5 kΩ
terminating resistor. Each receiver provides 0.5V hysteresis (typical) for noise immunity.
R1
OUT
, R2
OUT
:
Receiver outputs at TTL/CMOS levels.
C1+, C1-, C2+, C2-:
Charge pump capacitor inputs. These pins require two external capacitors (0.1
μF
minimum, 10
μF
maximum and should be the same size as C3 and C4). Capacitor 1 is connected between
C1+ and C1-. Capacitor 2 is connected between C2+ and C2-. Capacitor C1 can be omitted if +12 volts is
connected directly to V+. Likewise, C2 can be omitted if -12V is connected directly to V-.
DUAL CHARGE PUMP CONVERTERS
The DS232A has a two-stage on-board charge pump circuit that is used to generate
±10
volts from a
single +5-volt supply. In the first stage, capacitor C1 doubles the +5V supply to +10 volts which is then
stored on capacitor C3. The second stage uses capacitor C2 to invert the +10V potential to -10V. This
charge is then stored on capacitor C4. The
±10-volt
supplies allow the DS232A to provide the necessary
output levels for RS-232 communication. The DS232A will operate with charge pump capacitors as low
as 0.1
μF.
Larger capacitors (up to 10
μF)
can be used to reduce supply ripple.
RS-232 DRIVERS
The two RS-232 drivers are powered by the internal
±10-volt
supplies generated by the on-board charge
pump. The driver inputs are both TTL and CMOS compatible. Each input has an internal 400 kΩ pullup
resistor so that unused transmitter inputs can be left unconnected. The open circuit output voltage swing
is from (V+ - 0.6) to V- volts. Worst case conditions for EIA-232E/V.28 of
±5-volt
driving a 3 kΩ load
and 2500 pF are met at maximum operating temperature and V
CC
equal to 4.5 volts. Typical voltage
swings of
±8
volts occur when loaded with a nominal 5 kΩ RS-232 receiver. As required by EIA-232E
and V.28 specifications, the slew rate at the output is limited to less than 30 volts/μs. Typical slew rates
are 20 volts/μs unloaded and 12 volts/μs with 3 kΩ and 2500 pF load. These slew rates allow for bit rates
of over 250k bits/s. Driver outputs maintain high impedance when power is off.
RS-232 RECEIVERS
The two receivers conform fully to the RS-232E specifications. The input impedance is typically 5
kΩ and can withstand up to
±25
volts with or without V
CC
applied. The input switching thresholds are
within the
±3-volt
limit of RS-232E specification with an input threshold low of 0.8 volts and an input
threshold high of 2.4 volts. The receivers have 0.5 volts of hysteresis (typical) to improve noise rejection.
The TTL/CMOS compatible outputs of the receivers will be low whenever the RS-232 input is greater
than 2.4 volts. The receiver output will be high when the input is floating or driven between +0.8 volts
and -25 volts.
3 of 10
DS232A
ABSOLUTE MAXIMUM RATINGS*
Absolute Maximum Ratings
V
CC
V+
V-
Input Voltages
T
IN
R
IN
Output Voltages
T
OUT
R
OUT
Short Circuit Duration, T
OUT
*
-0.3V to +7.0V
(V
CC
-0.3V) to +14V
+0.3V to -14V
-0.3V to (V
CC
+0.3V)
±30V
(V+ + 0.3V) to (V- - 0.3V)
-0.3V to (V
CC
+ 0.3V)
Continuous
This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER
Operating Supply Voltage
SYMBOL
V
CC
MIN
4.5
TYP
MAX
5.5
(0°C to 70°C)
UNITS
V
NOTES
1
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Power Supply Current (No Load)
Power Supply Current (3 kΩ Load All
Outputs)
RS-232 Transmitters
Output Voltage Swing
Input Logic Threshold Low
Input Logic Threshold High
Maximum Data Rate
Logic Pullup/Input Current
Transmitter Output Resistance
Output Short-Circuit Current
V
ORS
V
TTL
V
TTH
f
D
I
PU
R
OUT
I
TSC
300
±15
250
±5
0.8
±8
1.4
1.4
350
5
10M
±30
±100
40
2.0
SYMBOL
I
CC1
I
CC2
MIN
TYP
4
15
MAX
10
(0°C to 70°C)
UNITS
mA
mA
NOTES
V
V
V
k bits/s
μA
Ω
mA
2
3
4
4 of 10
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