LT1780/LT1781
Low Power 5V RS232
Dual Driver/Receiver with
±15kV
ESD Protection
DESCRIPTIO
The LT
®
1780/LT1781 are dual RS232 driver/receiver pairs
with integral charge pump to generate RS232 voltage
levels from a single 5V supply. Using only 0.1µF external
capacitors, these circuits consume only 40mW of power,
and can operate to 120kbaud even while driving heavy
capacitive loads. New ESD structures on the chip allow the
LT1780/LT1781 to survive
±15kV
air gap and
±8kV
con-
tact ESD tests per IEC 1000-4-2, eliminating the need for
costly TransZorbs
®
on the RS232 line pins. The LT1780/
LT1781 are fully compliant with EIA RS232 standards.
Driver outputs are protected from overload, and can be
shorted to ground or up to
±30V
without damage. During
SHUTDOWN or power-off conditions, driver and receiver
outputs are in a high impedance state, allowing line
sharing.
The LT1780/LT1781 are direct upgrades to the LT1180A/
LT1181A, LT1280A/LT1281A and LT1381 for applications
which require the utmost ESD protection.
The LT1781 is available in 16-pin DIP,SO and SW pack-
ages. The LT1780 is supplied in 18-pin DIP and SW
packages for applications which require SHUTDOWN.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TransZorb is a registered trademark of General Instruments, GSI.
FEATURES
s
s
s
s
s
s
s
s
s
s
s
s
s
10mA Max Supply Current
ESD Protection to IEC 1000-4-2 Level 4
±
15kV Air Gap,
±
8kV Contact
Uses Small Capacitors: 0.1
µ
F
120kBaud Operation for R
L
= 3k, C
L
= 2500pF
250kBaud Operation for R
L
= 3k, C
L
= 1000pF
Outputs Withstand
±30V
Without Damage
CMOS Comparable Low Power: 40mW
Operates from a Single 5V Supply
Rugged Bipolar Design
Outputs Assume a High Impedance State When Off
or Powered Down
Meets All RS232 Specifications
Available With or Without Shutdown
Absolutely No Latch-up
APPLICATI
s
s
s
s
s
S
Portable Computers
Battery-Powered Systems
Power Supply Generator
Terminals
Modems
TYPICAL APPLICATI
2
0.1µF
4
LT1780
5
0.1µF
6
12
LOGIC
INPUTS
7
3
17
5V INPUT
V
+
OUT
0.1µF
V
–
OUT
0.1µF
DRIVER
OUTPUT
R
L
= 3k
C
L
= 2500pF
15
RS232 OUTPUT
11
13
8
14
5k
RECEIVER
OUTPUT
R
C
L
= 50pF
RS232 OUTPUT
RS232 INPUT
INPUT
LOGIC
OUTPUTS
10
18
9
5k
16
RS232 INPUT
ON/OFF
1780/81 • TA01
U
UO
UO
Output Waveforms
1780/81 • TA02
1
LT1780/LT1781
ABSOLUTE
AXI U
RATI GS
Supply Voltage (V
CC
) ................................................ 6V
V
+
........................................................................ 13.2V
V
–
...................................................................... –13.2V
Input Voltage
Driver ........................................................... V
–
to V
+
Receiver ............................................... – 30V to 30V
ON/OFF ................................................. – 0.3V to 12V
Output Voltage
Driver ...................................... V
+
– 30V to V
–
+ 30V
Receiver .................................... – 0.3V to V
CC
+ 0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC
C1
+
V
+
C1
–
C2
+
C2
–
V
–
TR2 OUT
REC2 IN
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
ON/OFF
V
CC
GND
TR1 OUT
REC1 IN
REC1 OUT
TR1 IN
TR2 IN
REC2 OUT
ORDER
PART
NUMBER
LT1780CN
LT1780CSW
N PACKAGE
18-LEAD PLASTIC DIP
SW PACKAGE
18-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 80°C/ W,
θ
JC
= 36°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 90°C/ W,
θ
JC
= 26°C/W (SW)
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Power Supply Generator
V
+
Output
V
–
Output
Supply Current (V
CC
)
Supply Current When OFF (V
CC
)
Supply Rise Time
SHUTDOWN to Turn-On
ON/OFF Pin Thresholds
ON/OFF Pin Current
Oscillator Frequency
Driver
Output Voltage Swing
Logic Input Voltage Level
CONDITIONS
(Note 2)
MIN
TYP
7.9
–7
8
q
q
(Note 3), T
A
= 25°C
SHUTDOWN (Note 4) LT1780 Only
C1 = C2 = C3 = C4 = 0.1µF
LT1780 Only
Input Low Level (Device SHUTDOWN)
Input High Level (Device Enabled)
0V
≤
V
ON/OFF
≤
5V
Load = 3k to GND
Input Low Level (V
OUT
= High)
Input High Level (V
OUT
= Low)
2
U
U
W
W W
U
W
(Note 1)
Short-Circuit Duration
V
+
................................................................... 30 sec
V
–
................................................................... 30 sec
Driver Output .............................................. Indefinite
Receiver Output .......................................... Indefinite
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
C1
+
V
+
C1
–
C2
+
C2
–
V
–
TR2 OUT
REC2 IN
1
2
3
4
5
6
7
8
16 V
CC
15 GND
14 TR1 OUT
13 REC1 IN
12 REC1 OUT
11 TR1 IN
10 TR2 IN
9
REC2 OUT
ORDER
PART
NUMBER
LT1781CN
LT1781CS
LT1781CSW
S PACKAGE
SW PACKAGE
N PACKAGE
16-LEAD PLASTIC DIP 16-LEAD PLASTIC SO 16-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 90°C/ W,
θ
JC
= 46°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 95°C/ W,
θ
JC
= 34°C/W (S)
T
JMAX
= 125°C,
θ
JA
= 95°C/ W,
θ
JC
= 27°C/W (SW)
MAX
UNITS
V
V
mA
mA
µA
ms
ms
V
V
µA
kHz
V
V
V
V
q
q
q
0.8
– 15
1
0.2
0.2
1.2
1.6
130
10
14
10
2.4
80
Positive
Negative
q
q
q
q
5.0
7.5
– 6.3
1.4
1.4
–5
0.8
2.0
LT1780/LT1781
ELECTRICAL CHARACTERISTICS
PARAMETER
Logic Input Current
Output Short-Circuit Current
Output Leakage Current
Data Rate
Slew Rate
Propagation Delay
Receiver
Input Voltage Thresholds
Hysteresis
Input Resistance
Output Leakage Current
Output Voltage
Output Short-Circuit Current
Propagation Delay
V
IN
=
±10V
CONDITIONS
0.8V
≤
V
IN
≤
2.0V
V
OUT
= 0V
(Note 2)
MIN
q
TYP
5
17
10
MAX
20
100
UNITS
µA
mA
µA
kBaud
kBaud
±7
q
SHUTDOWN V
OUT
=
±30V
(Note 4)
R
L
= 3k, C
L
= 2500pF
R
L
= 3k, C
L
= 1000pF
R
L
= 3k, C
L
= 51pF
R
L
= 3k, C
L
= 2500pF
Output Transition t
HL
High-to-Low (Note 5)
Output Transition t
LH
Low-to-High
Input Low Threshold (V
OUT
= High)
Input High Threshold (V
OUT
= Low)
120
250
4
15
7
0.6
0.5
0.8
q
30
1.3
1.3
V/µs
V/µs
µs
µs
V
V
V
kΩ
µA
V
V
mA
mA
ns
ns
1.3
1.7
0.4
5
1
0.2
4.2
– 20
20
250
350
2.4
1
7
10
0.4
– 10
600
600
0.1
3
SHUTDOWN (Note 4) 0
≤
V
OUT
≤
V
CC
Output Low, I
OUT
= – 1.6mA
Output High, I
OUT
= 160µA (V
CC
= 5V)
Sinking Current, V
OUT
= V
CC
Sourcing Current, V
OUT
= 0V
Output Transition t
HL
High-to-Low (Note 6)
Output Transition t
LH
Low-to-High
q
q
q
3.5
10
The
q
denotes specifications which apply over the 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 and V
ON/OFF
= 3V, 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.
Note 4:
Supply current measurements in SHUTDOWN are performed with
V
ON/OFF
≤
0.1V.
Note 5:
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 6:
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).
3
LT1780/LT1781
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Maximum Output Voltage
vs Load Capacitance
8.0
7.5
PEAK OUTPUT VOLTAGE (V)
DRIVER OUTPUT VOLTAGE (V)
PEAK OUTPUT VOLTAGE (V)
7.0
20k BAUD
6.5
60k BAUD
6.0
5.5
5.0
0
1
2
3 4 5 6 7 8
LOAD CAPACITANCE (nF)
9
10
120k BAUD
Receiver Input Thresholds
3.00
2.75
THRESHOLD VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
–55 –25
INPUT LOW
INPUT HIGH
SUPPLY CURRENT (mA)
50
25
0
75
TEMPERATURE (°C)
ON/OFF Thresholds
3.0
2.5
THRESHOLD VOLTAGE (V)
2.0
1.5
1.0
OFF THRESHOLD
0.5
0
–55 –25
ON THRESHOLD
SUPPLY CURRENT (mA)
50
25
75
0
TEMPERATURE (°C)
4
U W
1780 • G01
Driver Minimum Output Voltage
vs Load Capacitance
–4.0
–4.5
120k BAUD
–5.0
60k BAUD
–5.5
–6.0
–6.5
–7.0
0
1
2
3 4 5 6 7 8
LOAD CAPACITANCE (nF)
9
10
20k BAUD
10
8
6
4
2
0
–2
–4
–6
–8
Driver Output Voltage
R
L
= 3k
V
CC
= 5.5V
V
CC
= 5V
V
CC
= 4.5V
OUTPUT HIGH
OUTPUT LOW
V
CC
= 4.5V
V
CC
= 5V
V
CC
= 5.5V
–10
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1780 • G02
1780 • G03
Supply Current vs Data Rate
50
2 DRIVERS ACTIVE
R
L
= 3k
C
L
= 2500pF
40
30
20
10
0
100
125
0
25
50
75
100
DATA RATE (kBAUD)
125
150
1780 • G04
1780 • G05
Supply Current
25
20
2 DRIVERS LOADED R
L
= 3k
15
1 DRIVER LOADED R
L
= 3k
10
NO LOAD
5
100
125
0
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1780 • G06
1780 • G07
LT1780/LT1781
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Leakage in Shutdown
100
SHORT-CIRCUIT CURRENT (mA)
30
25
ISC
+
20
15
ISC
–
10
5
0
–55 –25
(
µA)
10
LEAKAGE CURRENT
1
0.1
–55 –25
50
25
0
75
TEMPERATURE (°C)
Receiver Short-Circuit Current
50
SHORT-CIRCUIT CURRENT (mA)
40
SLEW RATE (V/µs)
30
RX ISC
+
20
10
0
–55 –25
50
25
75
0
TEMPERATURE (°C)
Shutdown to Driver Outputs
10V
DRIVER 1
OUTPUT
5V
GND
GND
DRIVER 2
OUTPUT
– 5V
– 10V
ON/OFF PIN
INPUT
1780 • G12
U W
Driver Short-Circuit Current
V
OUT
= 30V
V
OUT
= –30V
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
1780 • G08
1780 • G09
Slew Rate vs Load Capacitance
16
14
RX ISC
–
12
10
8
+SLEW
6
–SLEW
4
2
100
125
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
LOAD CAPACITANCE (nF)
1780 • G11
1780 • G10
Driver Output Waveforms
DRIVER OUTPUT
R
L
= 3k
C
L
= 2500pF
DRIVER OUTPUT
R
L
= 3k
1780 • G13
5
