1
LT1237
5V RS232 Transceiver with
Advanced Power Management and
One Receiver Active in Shutdown
s
One Receiver Remains Active While in Shutdown
s
ESD Protection over
15kV
s
Uses Small Capacitors: 0.1
F, 0.2
F, 1.0
F
s
60
A Supply Current in Shutdown
s
Pin Compatible with LT1137A
s
120kBaud Operation for R
L
= 3k, C
L
= 2500pF
s
250kBaud Operation for R
L
= 3k, C
L
= 1000pF
s
Operates to 120kBaud
s
CMOS Comparable Low Power 30mW
s
Operates from a Single 5V Supply
s
Easy PC Layout--Flowthrough Architecture
s
Rugged Bipolar Design
s
Outputs Assume a High Impedance State When Off
or Powered Down
s
Absolutely No Latchup
s
Available in SO and SSOP Packages
The LT
1237 is an advanced low power three driver, five
receiver RS232 transceiver. Included on the chip is a
shutdown pin for reducing supply current near zero.
During shutdown one receiver remains active to detect
incoming RS232 signals, for example, to wake up a
system.
The LT1237 is fully compliant with all EIA RS232 specifi-
cations. New ESD structures on the chip allow the LT1237
to survive multiple
15kV strikes, eliminating the need for
costly TransZorbs
on the RS232 line pins.
The LT1237 operates in excess of 120kbaud even driving
heavy capacitive loads. Two shutdown modes allow the
driver outputs to be shut down separately from the receiv-
ers for more versatile control of the RS232 interface.
During shutdown, drivers and receivers assume a high
impedance state.
s
Notebook Computers
s
Palmtop Computers
, LTC and LT are registered trademarks of Linear Technology Corporation.
TransZorb is a registered trademark of General Instruments, GSI
Output Waveforms
R
1237 TA02
RECEIVER
OUTPUT
C
L
= 50pF
INPUT
DRIVER
OUTPUT
R
L
= 3k
C
L
= 2500pF
LT1237 TA01
5V V
CC
1.0
F
2
0.1
F
0.1
F
TO
LINE
LT1237
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DRIVER 1 OUT
RX1 IN
DRIVER 2 OUT
RX2 IN
RX3 IN
RX4 IN
DRIVER 3 OUT
RX5 IN (LOW-Q)
ON/OFF
28
27
26
25
24
23
22
21
20
19
18
17
16
15
2
0.1
F
DRIVER 1 IN
RX1 OUT
DRIVER 2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DRIVER 3 IN
RX5 OUT (LOW-Q)
GND
DRIVER
DISABLE
RING DETECT IN
SHUTDOWN
CONTROL OUT
CONTROLLER OR
PROCESSOR
TO LOGIC
V
V
+
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LT1237
(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 .................................................... 30V to 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
LT1237C ................................................. 0
C to 70
C
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec)................. 300
C
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Power Supply Generator
V
+
Output
7.9
V
V
Output
7
V
Supply Current (V
CC
)
T
A
= 25
C (Note 3)
6
12
mA
q
6
14
mA
Supply Current when OFF (V
CC
)
Shutdown (Note 4)
q
0.06
0.15
mA
Driver Disable
3.00
mA
Supply Rise Time
C1 = C2 = 0.2
F,
2
ms
Shutdown to Turn-On
C
+
= 1.0
F, C
= 0.1
F
ON/OFF Pin Thresholds
Input Low Level (Drivers Enabled)
0.8
1.2
V
Input High Level (Drivers Disabled)
1.6
2.4
V
ON/OFF Pin Current
0V
V
ON/OFF
5V
q
15
80
A
DRIVER DISABLE Pin Thresholds
Input Low Level (Drivers Enabled)
q
0.8
1.4
V
Input High Level (Drivers Disabled)
q
1.4
2.4
V
DRIVER DISABLE Pin Current
0V
V
DRIVER DISABLE
5V
q
10
500
A
Oscillator Frequency
Driver Outputs Loaded R
L
= 3k
130
kHz
ELECTRICAL C
C
HARA TERISTICS
Consult factory for Industrial and Military grade parts.
LT1237CG
LT1237CNW
LT1237CSW
1
2
3
4
5
6
7
8
9
10
11
12
13
14
V
+
5V V
CC
C1
+
C1
DR1 OUT
RX1 IN
DR2 OUT
RX2 IN
RX3 IN
RX4 IN
DR3 OUT
RX5 IN
(LOW-Q)
ON/OFF
NC
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
C2
C2
+
DR1 IN
RX1 OUT
DR2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DR3 IN
RX5 OUT
(LOW-Q)
GND
DRIVER
DISABLE
NC
NW PACKAGE
28-LEAD (WIDE) PDIP
TOP VIEW
SW PACKAGE
28-LEAD (WIDE) PLASTIC SO
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 150
C,
JA
= 96
C/ W (G)
T
JMAX
= 150
C,
JA
= 56
C/ W (NW)
T
JMAX
= 150
C,
JA
= 85
C/ W (SW)
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. (Note 2)
3
LT1237
ELECTRICAL C
C
HARA TERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Any Driver
Output Voltage Swing
Load = 3k to GND
Positive
q
5.0
7.5
V
Negative
q
6.3
5.0
V
Logic Input Voltage Level
Input Low Level (V
OUT
= High)
q
1.4
0.8
V
Input High Level (V
OUT
= Low)
q
2.0
1.4
V
Logic Input Current
0.8V
V
IN
2V
q
5
20
A
Output Short-Circuit Current
V
OUT
= 0V
9
17
mA
Output Leakage Current
Shutdown V
OUT
=
30V (Note 4)
q
10
100
A
Data Rate (Note 7)
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/
s
R
L
= 3k, C
L
= 2500pF
4
7
V/
s
Propagation Delay
Output Transition t
HL
High to Low (Note 5)
0.6
1.3
s
Output Transition t
LH
Low to High
0.5
1.3
s
Any 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
q
0.1
0.4
1.0
V
Input Resistance
V
IN
=
10V
3
5
7
k
Output Leakage Current
Shutdown (Note 4) 0
V
OUT
V
CC
q
1
10
A
Receivers 1, 2, 3, 4
Output Voltage
Output Low, I
OUT
= 1.6mA
q
0.2
0.4
V
Output High, I
OUT
= 160
A (V
CC
= 5V)
q
3.5
4.2
V
Output Short-Circuit Current
Sinking Current, V
OUT
= V
CC
10
20
mA
Sourcing Current, V
OUT
= 0V
10
20
mA
Propagation Delay
Output Transition t
HL
High to Low (Note 6)
250
600
ns
Output Transition t
LH
Low to High
350
600
ns
Receiver 5 (LOW I
SUPPLY
RX)
Output Voltage
Output Low, I
OUT
= 500
A
q
0.2
0.4
V
Output High, I
OUT
= 160
A (V
CC
= 5V)
q
3.5
4.2
V
Output Short-Circuit Current
Sinking Current, V
OUT
= V
CC
2
4
mA
Sourcing Current, V
OUT
= 0V
2
4
mA
Propagation Delay
Output Transition t
HL
High to Low (Note 6)
1.0
3
s
Output Transition t
LH
Low to High
0.6
3
s
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 burst cycles. C
+
= 1.0
F, C
= 0.1
F, C1 = C2 = 0.2
F. All outputs
are open, with all driver inputs tied high.
Note 4: Measurements in shutdown are performed with V
ON/OFF
0.1V.
Supply current measurements using driver disable are performed with
V
DRIVER DISABLE
3V.
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).
Note 7: Data rate operation guaranteed by slew rate, short-circuit current
and propagation delay tests.
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. (Note 2)
4
LT1237
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
TEMPERATURE (C)
55
10
DRIVER OUTPUT VOLTAGE (V)
8
4
2
0
10
4
0
50
75
1237 G01
6
6
8
2
25
25
100
125
OUTPUT HIGH
OUTPUT LOW
R
L
= 3k
V
CC
= 5V
V
CC
= 4.5V
V
CC
= 4.5V
V
CC
= 5V
Driver Output Voltage
TEMPERATURE (C)
55
0.50
THRESHOLD VOLTAGE (V)
0.75
1.25
1.50
1.75
3.00
2.25
0
50
75
1237 G02
1.00
2.50
2.75
2.00
25
25
100
125
INPUT HIGH
INPUT LOW
Receiver Input Thresholds
DATA RATE (kBAUD)
0
0
SUPPLY CURRENT (mA)
20
30
40
60
25
50
125
150
1237 G03
70
80
50
10
75
100
3 DRIVERS ACTIVE
R
L
= 3k
C
L
= 2500pF
Supply Current vs Data Rate
DRIVER DISABLE Threshold
Supply Current in Shutdown
ON/OFF Thresholds
Supply Current
TEMPERATURE (C)
0
SUPPLY CURRENT (mA)
10
15
20
30
1237 G08
35
40
25
5
3 DRIVERS LOADED
R
L
= 3k
55
0
50
75
25
25
100
125
1 DRIVER LOADED
R
L
= 3k
NO LOAD
Driver Leakage in Shutdown
TEMPERATURE (C)
55
0
SUPPLY CURRENT (mA)
2
5
0
50
75
1237 G05
1
4
3
25
25
100
125
TEMPERATURE (C)
55
SUPPLY CURRENT (
A)
100
125
150
25
75
1237 G04
75
50
25
0
50
100
125
25
0
TEMPERATURE (C)
55
THRESHOLD VOLTAGE (V)
2.0
2.5
3.0
25
75
1237 G06
1.5
1.0
25
0
50
100
125
0.5
0
TEMPERATURE (C)
0.1
LEAKAGE CURRENT
(
A)
10
100
1237 G09
1
55
0
50
75
25
25
100
125
V
OUT
= 30V
V
OUT
= 30V
TEMPERATURE (C)
55
THRESHOLD VOLTAGE (V)
2.0
2.5
3.0
25
75
1237 G07
1.5
1.0
25
0
50
100
125
0.5
0
ON THRESHOLD
OFF THRESHOLD
Supply Current in Driver Disable
5
LT1237
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Receiver Short-Circuit Current
Driver Short-Circuit Current
TEMPERATURE (
C)
55
SHORT-CIRCUIT CURRENT (mA)
20
25
30
25
75
1237 G10
15
10
25
0
50
100
125
5
0
I
SC
+
I
SC
TEMPERATURE (
C)
55
0
SHORT-CIRCUIT CURRENT (mA)
20
50
0
50
75
1237 G11
10
40
30
25
25
100
125
RX1 TO RX4
I
SC
+
RX1 TO RX4
I
SC
RX5 I
SC
RX5 I
SC
+
Receiver Output Waveforms
DRIVER OUTPUT
R
L
= 3k
DRIVER OUTPUT
R
L
= 3k
C
L
= 2500pF
RX5 OUTPUT
C
L
= 50pF
1237 G12
RX1 TO RX4
OUTPUT
C
L
= 50pF
INPUT
1237 G13
INPUT
Driver Output Waveforms
PI FU CTIO S
U
U
U
V
CC
: 5V Input Supply Pin. This pin should be decoupled
with a 0.1
F ceramic capacitor close to the package pin.
Insufficient supply bypassing can result in low output
drive levels and erratic charge pump operation.
GND: Ground Pin.
ON/OFF: TTL/CMOS Compatible Operating Mode Control.
A logic low puts the device in the low power shutdown
mode. All three drivers and four receivers (RX1, RX2, RX3,
and RX4) assume a high impedance output state in shut-
down. Only receiver RX5 remains active while the trans-
ceiver is in shutdown. The transceiver consumes only
60
A of supply current while in shutdown. A logic high
fully enables the transceiver.
DRIVER DISABLE: This pin provides an alternate control
for the charge pump and RS232 drivers. A logic high on
this pin shuts down the charge pump and places all driver
outputs in a high impedance state. All five receivers remain
active under these conditions. Floating the driver disable
pin or driving it to a logic low level fully enables the
transceiver. A logic low on the ON/OFF pin supersedes the
state of the DRIVER DISABLE pin. Supply current drops to
3mA when in driver disable mode.
V
+
: Positive Supply Output (RS232 Drivers). V
+
2V
CC
1.5V. This pin requires an external charge storage capaci-
tor C
1.0
F, tied to ground or V
CC
. Larger value capaci-
tors may be used to reduce supply ripple. The ratio of the
capacitors on V
+
and V
should be greater than 5 to 1.
V
: Negative Supply Output (RS232 Drivers). V
(2V
CC
2.5V). This pin requires an external charge
storage capacitor C
0.1
F. See the Applications Infor-
mation section for guidance in choosing filter capacitors
for V
+
and V
.
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