1
LT1381
Low Power 5V RS232 Dual
Driver/Receiver with
0.1µF Capacitors
R
Output Waveforms
DRIVER
OUTPUT
R
L
= 3k
C
L
= 2500pF
RECEIVER
OUTPUT
C
L
= 50pF
INPUT
U
S
A
O
PPLICATI
■
Portable Computers
■
Battery-Powered Systems
■
Power Supply Generator
■
Terminals
■
Modems
U
A
O
PPLICATITYPICAL
D
U
ESCRIPTIO
S
FEATURE
■
ESD Protection over ±10kV
■
Low Cost
■
Uses Small Capacitors: 0.1µF
■
CMOS Comparable Low Power: 40mW
■
Operates from a Single 5V Supply
■
120kBaud Operation for R
L
= 3k, C
L
= 2500pF
■
250kBaud Operation for R
L
= 3k, C
L
= 1000pF
■
Rugged Bipolar Design
■
Outputs Assume a High Impedance State When
Powered Down
■
Absolutely No Latchup
■
Available in Narrow SO Package
5k
5k
0.1µF
LOGIC
INPUTS
LOGIC
OUTPUTS 9
12
10
11
5
4
3
1
15
8
13
7
14
6
2
16 5V INPUT
V
+
OUT
V
–
OUT
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
LT1381 • TA01
LT1381
0.1µF
0.1µF
0.1µF
+
+
+
+
S
, LTC and LT are registered trademarks of Linear Technology Corporation.
TransZorb
®
is a registered trademark of General Instruments, GSI
The LT
®
1381 is a dual RS232 driver/receiver pair with
integral charge pump to generate RS232 voltage levels
from a single 5V supply. The circuit features rugged
bipolar design to provide operating fault tolerance and
ESD protection unmatched by competing CMOS designs.
Using only 0.1µF external capacitors, the circuit con-
sumes only 40mW of power and can operate to 120kbaud
even while driving heavy capacitive loads. New ESD struc-
tures on the chip allow the LT1381 to survive multiple
±10kV strikes, eliminating the need for costly TransZorbs
®
on the RS232 line pins. Driver outputs are protected from
overload and can be shorted to ground or up to ±25V
without damage. During power-off conditions, driver and
receiver outputs are in a high impedance state, allowing
line sharing.
LT1381 • TA02
2
LT1381
A
U
G
W
A
W
U
W
ARBSOLUTEXI T
IS
WU
U
PACKAGE/ORDER I FOR ATIO
(Note 1)
Supply Voltage (V
CC
) ................................................ 6V
V
+
........................................................................ 13.2V
V
–
...................................................................... –13.2V
Input Voltage
Driver ........................................................... V
–
to V
+
Receiver ............................................... – 30V to 30V
Output Voltage
Driver ................................. (V
+
– 30V) to (V
–
+ 30V)
Receiver ................................. –0.3V to (V
CC
+ 0.3V)
Short-Circuit Duration
V
+
................................................................... 30 sec
V
–
................................................................... 30 sec
Driver Output.............................................. Indefinite
Receiver Output.......................................... Indefinite
Operating Temperature Range
LT1381C................................................. 0°C to 70°C
LT1381I .............................................. –40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT1381CN
LT1381CS
LT1381IS
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
C1
+
V
+
C1
–
C2
+
C2
–
V
–
TR2 OUT
REC2 IN
V
CC
GND
TR1 OUT
REC1 IN
REC1 OUT
TR1 IN
TR2 IN
REC2 OUT
N PACKAGE
16-LEAD PLASTIC DIP S PACKAGE
16-LEAD PLASTIC SOIC
T
JMAX
= 125°C, θ
JA
= 90°C/W, θ
JC
= 46°C/W (N)
T
JMAX
= 125°C, θ
JA
= 110°C/ W, θ
JC
= 34°C/W (S)
Consult factory for Military grade parts.
(Note 2)
ELECTRICAL C CHARA TERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supply Generator
V
+
Output 7.9 V
V
–
Output –7.0 V
Supply Current (V
CC
) (Note 3), T
A
= 25°C814mA
●16 mA
Supply Rise Time C1 = C2 = C3 = C4 = 0.1µF 0.2 ms
Oscillator Frequency 130 kHz
Driver
Output Voltage Swing Load = 3k to GND Positive ●5.0 7.5 V
Negative ●–6.3 –5.0 V
Logic Input Voltage Level Input Low Level (V
OUT
= High) ●1.4 0.8 V
Input High Level (V
OUT
= Low) ●2.0 1.4 V
Logic Input Current 0.8V ≤ V
IN
≤ 2.0V ●520 µA
Output Short-Circuit Current V
OUT
= 0V 9 17 mA
Output Leakage Current Power Off V
OUT
= ±15V ●10 100 µA
Data Rate R
L
= 3k, C
L
= 2500pF 120 kBaud
R
L
= 3k, C
L
= 1000pF 250 kBaud
Slew Rate R
L
= 3k, C
L
= 51pF 15 30 V/µs
R
L
= 3k, C
L
= 2500pF 4 6 V/µs
Propagation Delay Output Transition t
HL
High to Low (Note 4) 0.6 1.3 µs
Output Transition t
LH
Low to High 0.5 1.3 µs
3
LT1381
PARAMETER CONDITIONS MIN TYP MAX UNITS
Receiver
Input Voltage Thresholds Input Low Threshold (V
OUT
= High) 0.8 1.3 V
Input High Threshold (V
OUT
= Low) 1.7 2.4 V
Hysteresis ●0.1 0.4 1.0 V
Input Resistance (Note 6) 3 5 7 kΩ
Output Voltage Output Low, I
OUT
= –1.6mA ●0.2 0.4 V
Output High, I
OUT
= 160µA (V
CC
= 5V) ●3.5 4.2 V
Output Short-Circuit Current Sinking Current, V
OUT
= V
CC
–10 mA
Sourcing Current, V
OUT
= 0V 10 20 mA
Propagation Delay Output Transition t
HL
High-to-Low (Note 5) 250 600 ns
Output Transition t
LH
Low-to-High 350 600 ns
ELECTRICAL C CHARA TERISTICS
(Note 2)
TYPICAL PERFOR A CE CHARACTERISTICS
WU
Driver Maximum Output Voltage
vs Load Capacitance
TEMPERATURE (°C)
–55
–10
DRIVER OUTPUT VOLTAGE (V)
–8
–4
–2
0
10
4
050 75
LT1381 • TPC03
–6
6
8
2
–25 25 100 125
RL = 3k
VCC = 5.5V
VCC = 5V
VCC = 4.5V
VCC = 4.5V
VCC = 5V
VCC = 5.5V
OUTPUT HIGH
OUTPUT LOW
Driver Minimum Output Voltage
vs Load Capacitance Driver Output Voltage
Note 4: For driver delay measurements, R
L
= 3k and C
L
= 51pF. Trigger
points are set between the driver’s input logic threshold and the output
transition to the zero crossing (t
HL
= 1.4V to 0V and t
LH
= 1.4V to 0V).
Note 5: For receiver delay measurements, C
L
= 51pF. Trigger points are
set between the receiver’s input logic threshold and the output transition
to standard TTL/CMOS logic threshold (t
HL
= 1.3V to 2.4V and t
LH
= 1.7V
to 0.8V).
Note 6: Tested at V
IN
= ±10V.
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: Testing done at V
CC
= 5V, unless otherwise specified.
Note 3: Supply current is measured as the average over several charge
pump cycles. C
+
= C
–
= C1 = C2 = 0.1µF. All outputs are open, with all
driver inputs tied high.
–20
LOAD CAPACITANCE (nF)
–7.0
PEAK OUTPUT VOLTAGE (V)
–6.0
–5.0
–4.0
2468
LT1381 • TPC02
1013579
–5.5
–4.5
–6.5
0
2 DRIVERS LOADED 120k BAUD
60k BAUD
20k BAUD
LOAD CAPACITANCE (nF)
0
PEAK OUTPUT VOLTAGE (V)
8.0
9.0
8
LT1381 • TPC01
7.0
6.0
5.0 24610
7.5
8.5
6.5
5.5
7
1359
2 DRIVERS LOADED
20k BAUD
60k BAUD
120k BAUD
4
LT1381
TYPICAL PERFOR A CE CHARACTERISTICS
WU
TEMPERATURE (°C)
–55
0.50
THRESHOLD VOLTAGE (V)
0.75
1.25
1.50
1.75
3.00
2.25
050 75
LT1381 • TPC04
1.00
2.50
2.75
2.00
–25 25 100 125
INPUT HIGH
INPUT LOW
Receiver Input Threshold Supply Current vs Data Rate
DATA RATE (kBaud)
0
0
SUPPLY CURRENT (mA)
10
20
30
40
50
25 50 75 100
LT1381 • TPC05
125 150
2 DRIVERS ACTIVE
R
L
= 3k
C
L
= 2500pF
Driver Leakage in Shutdown
TEMPERATURE (°C)
0.1
LEAKAGE CURRENT (µA)
10
100
LT1381 • TPC06
1
–55 0 50 75
–25 25 100 125
V
OUT
= –30V
V
OUT
= 30V
Receiver Short-Circuit Current
TEMPERATURE (°C)
–55
0
SHORT-CIRCUIT CURRENT (mA)
20
50
050 75
LTLT1381 • TPC07
10
40
30
–25 25 100 125
ISC
–
ISC
+
Driver Short-Circuit Current Slew Rate vs Load Capacitance
V+ Compliance Curve
LOAD CURRENT
+
(mA)
0
0
V
+
(V)
2
4
6
8
10
510
LT1381 • TPC10
15
V
+
(0.1µF)
V
+
(1µF)
TEMPERATURE (˚C)
–55
SHORT-CIRCUIT CURRENT (mA)
20
25
30
25 75
LT1381 • TPC08
15
10
–25 0 50 100 125
5
0
ISC
+
ISC
–
CAPACITANCE (nF)
0
SLEW RATE (V/µs)
12
16
20
4
LT1381 • TPC09
8
4
01235
10
14
18
6
2
+SLEW RATE
–SLEW RATE
V– Compliance Curve
LOAD CURRENT
–
(mA)
0
0
V
–
(V)
–2
–4
–6
–8
–10
510
LT1381 • TPC11
15
V
–
(0.1µF)
V
–
(1µF)
5
LT1381
PI FU CTIO S
U
UU
C1
+
, C1
–
, C2
+
, C2
–
(Pins 1, 3, 4, 5): Commutating
Capacitor Inputs. These pins require two external capaci-
tors C ≥ 0.1µF: one from C1
+
to C1
–
and another from C2
+
to C2
–
. C1 may be deleted if a separate 12V supply is
available and connected to pin C1
+
.
V
+
(Pin 2): Positive Supply Output (RS232 Drivers).
V
+
≈ 2V
CC
– 2.1V. This pin requires an external charge
storage capacitor C ≥ 0.1µF, tied to ground or V
CC
. Larger
value capacitors may be used to reduce supply ripple. With
multiple transceivers, the V
+
and V
–
pins may be paralleled
into common capacitors.
V
–
(Pin 6): Negative Supply Output (RS232 Drivers).
V
–
≈ –(2V
CC
– 3V). This pin requires an external charge
storage capacitor C ≥ 0.1µF. Larger value capacitors may
be used to reduce supply ripple. With multiple transceiv-
ers, the V
+
and V
–
pins may be paralleled into common
capacitors.
TR2 OUT, TR1 OUT (Pin 7, 14): Driver Outputs at RS232
Voltage Levels. Driver output swing meets RS232 levels
for loads up to 3k. Slew rates are controlled for lightly
loaded lines. Output current capability is sufficient for
load conditions up to 2500pF. Outputs are in a high
impedance state when V
CC
= 0V. Outputs are fully short-
circuit protected from V
–
+ 25V to V
+
– 25V. Applying
higher voltages will not damage the device if the over-
drive is moderately current limited. Short circuits on one
output can load the power supply generator and may
disrupt the signal levels of the other outputs. The driver
outputs are protected against ESD to ±10kV for human
body model discharges.
REC2 IN, REC1 IN (Pins 8, 13): Receiver Inputs. These
pins accept RS232 level signals (±30V) into a protected 5k
terminating resistor. The receiver inputs are protected
against ESD to ±10kV for human body model discharges.
Each receiver provides 0.4V of hysteresis for noise immu-
nity. Open receiver inputs assume a logic low state.
REC2 OUT, REC1 OUT (Pins 9, 12): Receiver Outputs with
TTL/CMOS Voltage Levels. Outputs are fully short-circuit
protected to ground or V
CC
with the power ON or OFF.
TR2 IN, TR1 IN (Pins 10, 11): RS232 Driver Input Pins.
These inputs are TTL/CMOS compatible. Inputs should
not be allowed to float. Tie unused inputs to V
CC
.
GND (Pin 15): Ground Pin.
V
CC
(Pin 16): 5V Input Supply Pin. This pin should be
decoupled with a 0.1µF ceramic capacitor close to the
package pin. Insufficient supply bypassing can result in
low output drive levels and erratic charge pump operation.
ESD PROTECTIO
U
The RS232 line inputs of the LT1381 have on-chip protec-
tion from ESD transients up to ±10kV. The protection
structures act to divert the static discharge safely to
system ground. In order for the ESD protection to function
effectively, the power supply and ground pins of the circuit
must be connected to ground through low impedances.
The power supply decoupling capacitors and charge pump
storage capacitors provide this low impedance in normal
application of the circuit. The only constraint is that low
ESR capacitors must be used for bypassing and charge
storage. ESD testing must be done with pins V
CC
, V
+
, V
–
and GND shorted to ground or connected with low ESR
capacitors.
ESD Test Circuit
LT1381 • ESD TC
0.1µF
RS232
LINE PINS
PROTECTED
TO ±10kV
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
0.1µF
0.1µF
0.1µF
C1
+
V
+
C1
–
C2
+
C2
–
V
–
TR2 OUT
LT1381 0.1µF
5V V
CC
GND
TR1 OUT
REC1 IN
REC1 OUT
TR1 IN
TR2 IN
RS232
LINE PINS
PROTECTED
TO ±10kV
REC2 IN REC2 OUT
++
+
+
+
6
LT1381
TYPICAL APPLICATIO S
U
Isolated RS232 Driver/Receiver
I
LIM
LT1111
FB
SW2
V
IN
SW1
GND
1N5818
L1
20µH
CTX20-1
1:1
47Ω
10k
1k
1N5818
100µF
1ΩLT1121-5
100µF
V
IN
= 5V
±10% FROM
SYSTEM 5V ±10%
V
CC
GND1
IN
GND2
13.7V
LT1381
RS232
GND2
OS
GND1
V
CC
OS
IN
1
3
4
5
16
2
6
98
11 14
RS232 INPUT
RS232 OUTPUT
V
OUT
V
IN
ISOLATOR OUTPUT
(DATA TO SYSTEM)
ISOLATOR INPUT
(DATA FROM SYSTEM)
LTC1145
LTC1145
ISOLATION BARRIER
FLOATING GROUND
LT1381 • TA03
R
X
D
X
V
CC
15
SYSTEM GROUND
+
+
10µF
+
0.1µF
+
0.1µF
+
0.1µF
+
0.1µF
+
1µF
0.1µF
+
ISOLATOR
OUTPUT
RS232
INPUT
ISOLATOR
INPUT
RS232
OUTPUT
Data Transmission Across Isolation Barrier
1381 TA04 1381 TA05
7
LT1381
PACKAGE DESCRIPTIO
U
Dimensions in inches (millimeters) unless otherwise noted.
N Package
16-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
N16 1197
0.255 ± 0.015*
(6.477 ± 0.381)
0.770*
(19.558)
MAX
16
12345678
910
11
12
13
14
15
0.020
(0.508)
MIN
0.125
(3.175)
MIN
0.130 ± 0.005
(3.302 ± 0.127)
0.065
(1.651)
TYP
0.045 – 0.065
(1.143 – 1.651)
0.018 ± 0.003
(0.457 ± 0.076)
0.100 ± 0.010
(2.540 ± 0.254)
0.009 – 0.015
(0.229 – 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.325 +0.035
–0.015
+0.889
–0.381
8.255
()
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
0.016 – 0.050
0.406 – 1.270
0.010 – 0.020
(0.254 – 0.508)× 45°
0° – 8° TYP
0.008 – 0.010
(0.203 – 0.254)
12345678
0.150 – 0.157**
(3.810 – 3.988)
16 15 14 13
0.386 – 0.394*
(9.804 – 10.008)
0.228 – 0.244
(5.791 – 6.197)
12 11 10 9
S16 0695
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
S Package
16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of circuits as described herein will not infringe on existing patent rights.
8
LT1381
LINEAR TECHNOLOGY C ORPORATION 1993
TYPICAL APPLICATIO S
U
RELATED PARTS
1381fa, sn1381 LT/TP 1098 REV A 2K • PRINTED IN USA
PART NUMBER DESCRIPTION COMMENTS
LT1180A/LT1181A 5V 2-Driver/2-Receiver RS232 Transceivers Pin Compatible with LT1280A/LT1280A
LT1280A/LT1281A 5V 2-Driver/2-Receiver RS232 Transceivers Pin Compatible with LT1180A/LT1181A
LT1780/LT1781 5V 2-Driver/2-Receiver RS232 Transceivers IEC 1000-4-2 Level 4 Compliance
Operation Using 5V and 12V Power Supplies
Sharing Capacitors
16
11
10
12
2
14
13
98
14
5k
5k
6
7
5
3
V
+
V
–
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
C2
+
C2
–
C1
–
C1
+
TTL OUTPUT
TTL OUTPUT
TTL INPUT
TTL INPUT
5V V
CC
LT1381
LT1381 • TA07
0.1µF
+
0.1µF
+
+
+
16
11
10
12
2
14
13
98
14
5k
5k
6
7
5
3
V
+
V
–
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
C2
+
C2
–
C1
–
C1
+
TTL OUTPUT
TTL OUTPUT
TTL INPUT
TTL INPUT
5V V
CC
LT1381
0.1µF
0.1µF
+
0.1µF
+
5k
5k
S
LOGIC
INPUTS
LOGIC
OUTPUTS 9
12
10
11
5
4
2
1
15
8
13
7
14
16
3
16 5V INPUT
–12V
OUT
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
LT1381 • TA06
LT1381
12V INPUT
0.1µF
+
0.1µF
+
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
