1
LTC1348
3.3V/5V Low Power RS232
3-Driver/5-Receiver Transceiver
S
FEATURE
D
U
ESCRIPTIO
■
Low Supply Current: 600µA at 3.3V
■
Supply Current in Shutdown: 0.2µA
■
Supply Current in Receiver Alive Mode: 15µA
■
ESD Protection over ±10kV
■
Operates from a Single 3V to 5.5V Supply
■
Operates to 120kBaud with 0.1µF Flying Capacitors
■
Three-State Outputs Are High Impedance When Off
■
Output Overvoltage Does Not Force Current
Back into Supplies
■
RS232 I/O Lines Can Be Forced to ±25V
Without Damage
■
Flowthrough Architecture
The LTC
®
1348 is a 3-driver/5-receiver RS232 transceiver
with very low supply current. The charge pump only
requires five 0.1µF capacitors. The LTC1348 provides full
RS232 output levels when operated over a wide supply
range of 3V to 5.5V
The transceiver operates in one of four modes: Normal,
Receiver Disable, Receiver Alive and Shutdown. In Normal
or Receiver Disable mode, I
CC
is only 600µA at 3.3V and
800µA at 5V in the no load condition. In Shutdown mode,
the supply current is further reduced to 0.2µA. In Receiver
Alive mode, all five receivers are kept alive and the supply
current is 15µA. All RS232 outputs assume a high imped-
ance state in Shutdown or Receiver Alive mode or with the
power off. The receiver outputs assume a high impedance
state in Receiver Disable or with the power off.
The LTC1348 is fully compliant with all data rate and
overvoltage RS232 specifications. The transceiver oper-
ates up to 120kbaud with all drivers loaded with 1000pF,
3kΩ. Both driver outputs and receiver inputs can be forced
to ±25V without damage and can survive multiple ±10kV
ESD strikes.
U
S
A
O
PPLICATI
■
Notebook Computers
■
Palmtop Computers
■
Printers
■
Portable Instruments
LT1348 • TA01
C5
0.1µFC2
0.1µFC3
0.1µF
C4
0.1µF
LTC1348
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DR 1 OUT
RX1 IN
DR 2 OUT
RX2 IN
RX3 IN
RX4 IN
DR 3 OUT
RX5 IN
28
27
26
25
24
23
22
21
20
19
18
17
16
15
DR 1 IN
RX1 OUT
DR 2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DR 3 IN
RX5 OUT
DREN
RXEN
V
–
V
+
V
CC
GND
C1
0.1µF
3-Drivers/5-Receivers with Shutdown
U
A
O
PPLICATITYPICAL
Supply Current
, LTC and LT are registered trademarks of Linear Technology Corporation.
TEMPERATURE (˚C)
–40
SUPPLY CURRENT (mA)
1.4
20
LT1348 •TA02
0.8
0.4
–20 0 40
0.2
0
1.6
1.2
1.0
0.6
SHUTDOWN CURRENT (µA)
1.4
0.8
0.4
0.2
0
1.6
1.2
1.0
0.6
60 80
QUIESCENT
CURRENT
SHUTDOWN
CURRENT
V
CC
= 5V
V
CC
= 3.3V
V
CC
= 3.3V
OR 5V
2
LTC1348
A
U
G
W
A
W
U
W
ARBSOLUTEXI T
I
S
WU
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
LTC1348CG
LTC1348CSW
LTC1348IG
LTC1348ISW
(Note 1)
Supply Voltage (V
CC
) ................................................ 6V
Input Voltage
Driver ....................................... –0.3V to V
CC
+ 0.3V
Receiver ............................................... – 25V to 25V
Driver/Receiver Enable Pin ........ –0.3V to V
CC
+ 0.3V
Output Voltage
Driver ................................................... –25V to 25V
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
LTC1348C................................................ 0°C to 70°C
LTC1348I............................................ –40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°CConsult factory for Military grade parts.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
V
+
C2
+
C2
–
V
CC
C1
+
C1
–
DR1 OUT
RX1 IN
DR2 OUT
RX2 IN
RX3 IN
RX4 IN
DR3 OUT
RX5 IN
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
–
C3
+
C3
–
DR1 IN
RX1 OUT
DR2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DR3 IN
RX5 OUT
DREN
RXEN
GND
TOP VIEW
SW PACKAGE
28-LEAD PLASTIC SO
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C, θ
JA
= 96°C/W (G)
T
JMAX
= 125°C, θ
JA
= 85°C/W (SW)
ELECTRICAL C CHARA TERISTICSCD
VCC = 3V to 5.5V, C1 to C4 = 0.1µF, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Any Driver
Output Voltage Swing V
CC
= 3.3V, 3k to GND Positive ● 5.0 6.2 V
Negative ●–5.0 – 6.0 V
Logic Input Voltage Level Input Low Level (V
OUT
= High) ●0.8 V
Input High Level (V
OUT
= Low), V
CC
= 3.3V ●2.0 V
Input High Level (V
OUT
= Low), V
CC
= 5V ●2.4 V
Logic Input Current V
IN
= V
CC
● 5 µA
V
IN
= 0V ●–5 –35 µA
Output Short-Circuit Current V
OUT
= 0V ±12 mA
Output Leakage Current Shutdown (Note 3) or Receiver Alive Mode (Note 4), ●±10 ±500 µA
V
OUT
= ±20V
Any Receiver
Input Voltage Thresholds Input Threshold (Receiver Alive Mode) 0.8 1.5 2.4 V
Input Low Threshold (Normal Mode) 0.8 1.3 V
Input High Threshold (Normal Mode) 1.7 2.4 V
Hysteresis Normal Mode 0.3 V
Input Resistance V
IN
= ±10V 3 5 7 kΩ
Output Voltage Output Low, I
OUT
= – 1.6mA ●0.2 0.4 V
Output High, I
OUT
= 160µA●V
CC
– 0.6V V
Output Short-Circuit Current Sinking Current, V
OUT
= V
CC
–3 –20 mA
Output Leakage Current Shutdown (Note 3), 0V ≤ V
OUT
≤ V
CC
●110 µA
3
LTC1348
ELECTRICAL C CHARA TERISTICSCD
VCC = 3V to 5.5V, C1 to C4 = 0.1µF, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supply Generator
V
+
Output Voltage I
OUT
= 0mA 8.0 V
I
OUT
= 8mA 7.5 V
V
–
Output Voltage I
OUT
= 0mA –8.0 V
I
OUT
= –8mA –7.0 V
Supply Rise Time Shutdown to Turn-On 0.2 ms
Power Supply
V
CC
Supply Current No Load (Note 2) V
CC
= 3.3V ●0.6 2.0 mA
No Load (Note 2) V
CC
= 5V ●0.8 2.5 mA
Receiver Alive Mode (Note 4) V
CC
= 3.3V or 5V ●15 30 µA
Supply Leakage Current (V
CC
) Shutdown (Note 3) ●0.2 10 µA
Driver/Receiver Enable Threshold Low ●0.8 V
Driver/Receiver Enable Threshold High V
CC
= 3.3V ●2.0 V
Driver/Receiver Enable Threshold High V
CC
= 5V ●2.4 V
AC ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Maximum Data Rate R
L
= 3k, C
L
= 1000pF, One Driver Switching 120 250 kbps
Slew Rate V
CC
= 5V, R
L
= 3k, C
L
= 51pF 8 30 V/µs
V
CC
= 3.3V, R
L
= 3k, C
L
= 2500pF 3 V/µs
Driver Propagation Delay t
HLD
(Figure 1) ●2.5 4 µs
(TTL to RS232) t
LHD
(Figure 1) ●2.5 4 µs
Receiver Propagation Delay t
HLR
(Figure 2) (Normal Mode) ●0.3 1 µs
(RS232 to TTL) t
LHR
(Figure 2) (Normal Mode) ●0.2 1 µs
t
HLR
(Figure 2) (Receiver Alive Mode) ●1.0 4 µs
t
LHR
(Figure 2) (Receiver Alive Mode) ●0.2 4 µs
Note 3: Supply current measurement in Shutdown is performed with
V
DREN
and V
RXEN
= 0V.
Note 4: Supply current measurement in Receiver Alive mode is performed
with V
DREN
= 0V and V
RXEN
= V
CC
.
VCC = 3V to 5.5V, C1 to C4 = 0.1µF, unless otherwise noted.
The ● denotes specifications which apply over the full operating
temperature range (0°C ≤ T
A
≤ 70°C for Commercial grade and
–40°C ≤ T
A
≤ 85°C for Industrial grade).
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: Supply current is measured with driver and receiver outputs
unloaded. The V
DREN
and V
RXEN
= V
CC
.
4
LTC1348
TYPICAL PERFORMANCE CHARACTERISTICS
UW
Driver Output Voltage High/Low
vs Load Capacitance (CL)Supply Current
vs Driver Data Rate
Driver Output Voltage High/Low
vs Load Capacitance (CL)
Driver Output Voltage High/Low
vs Temperature (°C)
TEMPERATURE (°C)
0
0
LEAKAGE CURRENT (µA)
5
15
20
25
50
45
LTC1348 G06
10
2010 30 40 60 70
30
35
40
V
OUT
= –20V
V
OUT
= 20V
V
CC
= 3.3V
LOAD CAPACITANCE (pF)
0
–7
DRIVER OUTPUT VOLTAGE HIGH/LOW
–5
–3
–1
7
6
4
2
0
–2
–4
–6
3
1000 2000 5000
5
1
3000 4000
250kbps
250kbps
120kbps
120kbps
64kbps
64kbps 20kbps
20kbps
VCC = 3.3V
0.1µF FLYING CAPACITORS
ALL DRIVERS LOADED 3kΩ + CL
1 DRIVER DRIVEN
LTC1348 G01
OUTPUT HIGH
OUTPUT LOW
LOAD CAPACITANCE (pF)
0
–7
DRIVER OUTPUT VOLTAGE HIGH/LOW
–5
–3
–1
7
6
4
2
0
–2
–4
–6
3
1000 2000 5000
5
1
3000 4000
120kbps
120kbps
64kbps
64kbps
20kbps
VCC = 3.3V
0.1µF FLYING CAPACITORS
ALL DRIVERS DRIVEN AND 
LOADED 3kΩ + CL
LTC1348 G02
OUTPUT HIGH
OUTPUT LOW
20kbps
Driver Leakage in SHUTDOWN
vs Temperature (°C)
TEMPERATURE (°C)
0
–7
DRIVER OUTPUT VOLTAGE HIGH/LOW
–5
–3
–1
7
6
4
2
0
–2
–4
–6
3
10 20 30 70
5
1
40 50 60
LTC1348 G04
V
CC
= 3V
V
CC
= 3V
V
CC
= 3.3V
OUTPUT HIGH
OUTPUT LOW
V
CC
= 3.3V
ALL DRIVERS
LOADED WITH 3kΩ
Driver Short-Circuit Current
vs Temperature (°C)
With VCC = 3.3V
All Driver Outputs Loaded with
3kΩ, 1000pF. 1 Driven at 250kbps
DRIVER DATA RATE
0
SUPPLY CURRENT (mA)
30
40
50
200
LTC1348 G03
20
10
050 100 150 250
3 OUTPUT LOADED
3kΩ // 2500pF
1 OUTPUT LOADED
3kΩ // 2500pF
V
CC
= 3.3V
TEMPERATURE (°C)
–40
0
SHORT-CIRCUIT CURRENT (mA)
4
8
10
12
60
20
LTC1348 G05
6
0–20 20 40 80 100
14
16
18
I
SC–
I
SC+
V
CC
= 3.3V
LTC1348 G07
DRIVER
INPUT
DRIVEN DRIVER
OUTPUT
5
LTC1348
PI FU CTIO S
U
UU
V
CC
: 3V to 5.5V Input Supply Pin. This pin should be
decoupled with a 0.1µF ceramic capacitor.
GND: Ground Pin.
RXEN: TTL/CMOS Compatible Enable Pin. Refer to Table
1 for its functional description.
DREN: TTL/CMOS Compatible Enable Pin. Refer to Table
1 for its functional description.
V
+
: Positive Supply Output (RS232 Drivers). This pin
requires an external capacitor C = 0.1µF for charge stor-
age. The capacitor may be tied to ground or V
CC
. With
multiple devices, the V
+
and V
–
pins may be paralleled into
common capacitors. For large numbers of devices, in-
creasing the size of the shared common storage capaci-
tors is recommended to reduce ripple.
V
–
: Negative Supply Output (RS232 Drivers). This pin
requires an external capacitor C = 0.1µF for charge
storage.
C1
+
, C1
–
, C2
+
, C2
–
, C3
+
, C3
–
: Commutating Capacitor
Inputs. These pins require three external capacitors C =
0.1µF: one from C1
+
to C1
–
, another from C2
+
to C2
–
and
another from C3
+
to C3
–
. To maintain charge pump
efficiency, the capacitor’s effective series resistance should
be less than 1Ω. Ceramic capacitors are recommended.
DR IN: RS232 Driver Input Pins. Inputs are TTL/CMOS
compatible. The inputs of unused drivers can be left
unconnected since 300k input pull-up resistors to V
CC
are
included on chip. To minimize power consumption, the
internal driver pull-up resistors are disconnected from V
CC
in the Shutdown or Receiver Alive mode.
DR OUT: Driver Outputs at RS232 Voltage Levels. Outputs
are in a high impedance state when in the Shutdown,
Receiver Alive mode or V
CC
= 0V. The driver outputs are
protected against ESD to ±10kV for human body model
discharges.
RX IN: Receiver Inputs. These pins can be forced to ±25V
without damage. The receiver inputs are protected against
ESD to ±10kV for human body model discharges. Each
receiver provides 0.4V of hysteresis for noise immunity. In
Receiver Alive mode all receivers have no hysteresis.
RX OUT: Receiver Outputs with TTL/CMOS Voltage Lev-
els. Outputs are in a high impedance state when in the
Shutdown or Receiver Disable mode to allow data line
sharing.
Table 1. Functional Description
MODE RX ENABLE DR ENABLE DRIVERS RECEIVERS I
CC
TYP
Shutdown 0 0 All Drivers Shutdown. All Receivers Shutdown. 0.2µA
All Driver Outputs Assume High Impedance. All Receiver Outputs Assume High Impedance.
All Driver Pull-Up Resistors Disconnect
From V
CC
.
Receiver 0 1 All Drivers Alive. All Receiver Outputs in Three-State. 600µA at
Disable 3.3V,
800µA at
5V
Receiver 1 0 All Drivers Shutdown. All Receivers Alive. 15µA
Alive All Driver Outputs in Three-State.
All Driver Pull-Up Resistors Disconnect
From V
CC
.
Normal 1 1 All Drivers Alive. All Receivers Alive. 600µA at
3.3V,
800µA at
5V
6
LTC1348
Figure 1. Driver Propagation Delay Timing Figure 2. Receiver Propagation Delay Timing
SWITCHI G TI E WAVEFOR S
WWU
1.4V
0V
VCC
0V
V+
V–
0V
DRIVER
INPUT
DRIVER
OUTPUT
1.4V
t HLD
t LHD
LTC1348 • F01
0.8V
V
CC
0V
2.4V
RX
INPUT
RX
OUTPUT
1.3V
t
HLR
1.7V
t
LHR
LTC1348 • F02
V
CC
0V
APPLICATIONS INFORMATION
WUU U
TEST CIRCUITS
Figure 3. Driver Timing Test Load
RX
RX INPUT
51pF
RX
OUTPUT
LTC1348 • F04
Figure 4. Receiver Timing Test Load
DRIVER
DRIVER
INPUT
3k
51pF
DRIVER
OUTPUT
LTC1348 • F03
Power Supply
The LTC1348 includes an onboard voltage-tripling charge
pump capable of generating ±8V from a single 3.3V
supply. This allows the LTC1348 drivers to provide guar-
anteed ±5V RS232-compliant voltage levels with a 3.3V
supply. With all outputs loaded with 3kΩ, the LTC1348
can typically swing ±5V with voltages as low as 2.85V. It
will meet the ±3.7V EIA562 levels with supply voltages as
low as 2.2V. The charge pump requires three external
flying capacitors to operate; 0.1µF ceramic capacitors are
adequate for most applications. For applications requiring
extremely high data rates or abnormally heavy output
loads, 0.33µF flying capacitors are recommended. Bypass
and output capacitor values should match those of the
flying capacitors and all capacitors should be mounted as
close to the package as possible.
LT1348 • TC
RS232 LINE PINS
PROTECTED TO ±10kV
0.1µF
0.1µF
0.1µF0.1µF
0.1µF
LTC1348
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DR1 OUT
RX1 IN
DR2 OUT
RX2 IN
RX3 IN
RX4 IN
DR3 OUT
RX5 IN
28
27
26
25
24
23
22
21
20
19
18
17
16
15
DR1 IN
RX1 OUT
DR2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DR3 IN
RX5 OUT
DREN
RXEN
V
–
V
+
V
CC
GND
0.1µF
C2
+
C3
+
C3
–
C2
–
C1
+
C1
–
ESD Test Circuit
7
LTC1348
APPLICATIONS INFORMATION
WUU U
DRIVER OUTPUT
RECEIVER OUTPUT
DRIVER INPUT
LTC1348 G06
DRIVER OUTPUT
RECEIVER OUTPUT
DRIVER INPUT
LTC1348 G07
LT1348 • F05
0.1µF
0.1µF0.1µF
0.1µF
LTC1348
1
2
3
4
5
6
7
8
9
10
11
12
13
14
RX1 IN
RX2 IN
RX3 IN
RX4 IN
RX5 IN
28
27
26
25
24
23
22
21
20
19
18
17
16
15
DR1 IN
RX1 OUT
DR2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DR3 IN
RX5 OUT
DREN
RXEN
V
–
V
+
V
CC
GND
0.1µF
0.1µF
1000pF
0.1µF0.1µF
0.1µF
LTC1348
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DR1 OUT
DR2 OUT
RX3 IN
RX4 IN
DR3 OUT
28
27
26
25
24
23
22
21
20
19
18
17
16
15
DRIVER 1 IN
RX1 OUT
DRIVER 2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DRIVER 3 IN
RX5 OUT
DREN
RXEN
V
–
V
+
V
CC
GND
0.1µF
DR1 OUT
DR2 OUT
RX5 IN
DR3 OUT
RX1 IN
1000pF
1000pF
RX2 IN
C2
+
C3
+
C3
–
C3
+
C3
–
C2
–
C1
+
C1
–
C2
+
C2
–
C1
+
C1
–
Figure 5. Data Rate Evaluation Circuit
Figure 6. Driver Test Result at 120kbps
Figure 7. Driver Test Results at 250kbps
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 its circuits as described herein will not infringe on existing patent rights.
High Data Rates
The LTC1348 maintains true RS232 ±5V minimum driver
output even at high data rates. Figure 5 shows a test circuit
with 2m wires connecting the two test chips. Both chips
are run from 3.3V supplies. Figure 6 shows the typical line
waveforms with all three drivers, loaded with 1000pF and
3kΩ, toggling simultaneously at 120kbaud. Figure 7 shows
the same circuit with a single 1000pF/3kΩ loaded driver
driven at 250kbaud, and the other two drivers loaded but
not toggling. This closely approximates the actual behav-
ior of an RS232 serial port, with only one driver (TX) driven
at high speed and the other two drivers (RTS and DTR)
driven at a relatively low data rate or at DC. Under the same
conditions, the LTC1348 can go as fast as 350kbaud and
still meet EIA562 (±3.7V) minimum driver output levels.
8
LTC1348
LINEAR TECHNOLOGY CORPORATION 1994
1348fa LT/GP 0197 5K REV A • PRINTED IN USA
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters) unless otherwise noted.
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT1137A 3-DR/5-RX RS232 Transceiver ±15kV IEC-801-2 ESD Protection
LTC1327 3-DR/5-RX RS562 Transceiver 3.3V Operation
LT1330 3-DR/5-RX RS232 3V Logic Interface
LT1331 3-DR/5-RX RS232/RS562 Transceiver 5V RS232 or 3V RS562 Operation
LTC1347 3-DR/5-RX Micropower RS232 Transceiver 5 Receivers Active in Shutdown
S28 (WIDE) 0396
0° – 8° TYP
NOTE 1
0.009 – 0.013
(0.229 – 0.330) 0.016 – 0.050
(0.406 – 1.270)
0.291 – 0.299**
(7.391 – 7.595)
× 45°
0.010 – 0.029
(0.254 – 0.737)
0.037 – 0.045
(0.940 – 1.143)
0.004 – 0.012
(0.102 – 0.305)
0.093 – 0.104
(2.362 – 2.642)
0.050
(1.270)
TYP 0.014 – 0.019
(0.356 – 0.482)
NOTE 1
0.697 – 0.712*
(17.70 – 18.08)
12345678
0.394 – 0.419
(10.007 – 10.643)
910
2526
11 12
22 21 20 19 18 17 16 152324
1413
2728
NOTE:
1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS
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
*
**
G Package
28-Lead Plastic SSOP (0.209)
(LTC DWG # 05-08-1640)
G28 SSOP 0694
0.005 – 0.009
(0.13 – 0.22)
0° – 8°
0.022 – 0.037
(0.55 – 0.95)
0.205 – 0.212**
(5.20 – 5.38)
0.301 – 0.311
(7.65 – 7.90)
12345678 9 10 11 12 1413
0.397 – 0.407*
(10.07 – 10.33)
2526 22 21 20 19 18 17 16 1523242728
0.068 – 0.078
(1.73 – 1.99)
0.002 – 0.008
(0.05 – 0.21)
0.0256
(0.65)
BSC 0.010 – 0.015
(0.25 – 0.38)
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH 
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD 
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
SW Package
28-Lead Plastic Small Outline (Wide 0.300)
(LTC DWG # 05-08-1620)
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
(408) 432-1900
FAX: (408) 434-0507
●
TELEX: 499-3977
●
www.linear-tech.com