LT1237
5V RS232 Transceiver with
Advanced Power Management and
One Receiver Active in Shutdown
FEATURES
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DESCRIPTIO
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One Receiver Remains Active While in Shutdown
ESD Protection over
±15kV
Uses Small Capacitors: 0.1µF, 0.2µF, 1.0µF
60µA Supply Current in Shutdown
Pin Compatible with LT1137A
120kBaud Operation for R
L
= 3k, C
L
= 2500pF
250kBaud Operation for R
L
= 3k, C
L
= 1000pF
Operates to 120kBaud
CMOS Comparable Low Power 30mW
Operates from a Single 5V Supply
Easy PC Layout—Flowthrough Architecture
Rugged Bipolar Design
Outputs Assume a High Impedance State When Off
or Powered Down
Absolutely No Latchup
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TransZorb is a registered trademark of General Instruments, GSI
APPLICATIO S
s
s
Notebook Computers
Palmtop Computers
TYPICAL APPLICATIO
V
+
1.0µF
2
×
0.1µF
DRIVER 1 OUT
RX1 IN
DRIVER 2 OUT
TO
LINE
RX2 IN
RX3 IN
RX4 IN
DRIVER 3 OUT
RX5 IN (LOW-Q)
ON/OFF
5V V
CC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
LT1237
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
–
0.1µF
2
×
0.1µF
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
µCONTROLLER
OR
µPROCESSOR
SHUTDOWN
CONTROL OUT
LT1237 TA01
RECEIVER
OUTPUT
C
L
= 50pF
DRIVER
OUTPUT
R
L
= 3k
C
L
= 2500pF
TO LOGIC
R
INPUT
U
Output Waveforms
1237 TA02
U
U
1
LT1237
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
+
1
5V V
CC
2
C1
+
3
C1
–
4
DR1 OUT 5
RX1 IN 6
DR2 OUT 7
RX2 IN 8
RX3 IN 9
RX4 IN 10
DR3 OUT 11
RX5 IN 12
(LOW-Q)
ON/OFF 13
NC 14
28 V
–
27 C2
–
26 C2
+
25 DR1 IN
24 RX1 OUT
23 DR2 IN
22 RX2 OUT
21 RX3 OUT
20 RX4 OUT
19 DR3 IN
RX5 OUT
18 (LOW-Q)
17 GND
16 DRIVER
DISABLE
15 NC
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
ORDER PART
NUMBER
LT1237CG
LT1237CNW
LT1237CSW
G PACKAGE
NW PACKAGE
28-LEAD PLASTIC SSOP 28-LEAD (WIDE) PDIP
SW PACKAGE
28-LEAD (WIDE) PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 96°C/ W (G)
T
JMAX
= 150°C,
θ
JA
= 56°C/ W (NW)
T
JMAX
= 150°C,
θ
JA
= 85°C/ W (SW)
Consult factory for Industrial and Military grade parts.
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 2)
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
DRIVER DISABLE Pin Thresholds
DRIVER DISABLE Pin Current
Oscillator Frequency
CONDITIONS
MIN
TYP
7.9
–7
6
6
0.06
3.00
2
0.8
q
q
q
q
ELECTRICAL CHARACTERISTICS
MAX
UNITS
V
V
mA
mA
mA
mA
ms
V
V
µA
V
V
µA
kHz
T
A
= 25°C (Note 3)
q
Shutdown (Note 4)
Driver Disable
C1 = C2 = 0.2µF,
C
+
= 1.0µF, C
–
= 0.1µF
Input Low Level (Drivers Enabled)
Input High Level (Drivers Disabled)
0V
≤
V
ON/OFF
≤
5V
Input Low Level (Drivers Enabled)
Input High Level (Drivers Disabled)
0V
≤
V
DRIVER DISABLE
≤
5V
Driver Outputs Loaded R
L
= 3k
q
12
14
0.15
1.2
1.6
1.4
1.4
130
–15
0.8
–10
2.4
80
2.4
500
2
U
W
U
U
W W
W
LT1237
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 2)
PARAMETER
Any Driver
Output Voltage Swing
Logic Input Voltage Level
Logic Input Current
Output Short-Circuit Current
Output Leakage Current
Data Rate (Note 7)
Slew Rate
Propagation Delay
Any Receiver
Input Voltage Thresholds
Hysteresis
Input Resistance
Output Leakage Current
Receivers 1, 2, 3, 4
Output Voltage
Output Short-Circuit Current
Propagation Delay
Receiver 5 (LOW I
SUPPLY
RX)
Output Voltage
Output Short-Circuit Current
Propagation Delay
CONDITIONS
Load = 3k to GND
Input Low Level (V
OUT
= High)
Input High Level (V
OUT
= Low)
0.8V
≤
V
IN
≤
2V
V
OUT
= 0V
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)
q
ELECTRICAL CHARACTERISTICS
MIN
Positive
Negative
q
q
q
q
q
TYP
7.5
– 6.3
1.4
1.4
5
17
10
MAX
UNITS
V
V
V
V
µA
mA
µA
kBaud
kBaud
V/µs
V/µs
µs
µs
V
V
V
kΩ
µA
V
V
mA
mA
ns
ns
V
V
mA
mA
µs
µs
5.0
– 5.0
0.8
20
100
2.0
±9
q
120
250
4
15
7
0.6
0.5
1.3
1.7
0.4
5
1
0.2
4.2
– 20
20
250
350
0.2
4.2
–4
4
1.0
0.6
30
1.3
1.3
0.8
0.1
3
V
IN
=
±10V
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
Output Low, I
OUT
= – 500µA
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
2.4
1.0
7
10
0.4
3.5
– 10
10
600
600
0.4
q
q
3.5
–2
2
3
3
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
+
= 1.0µF, C
–
= 0.1µF, C1 = C2 = 0.2µF. 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.
3
LT1237
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output Voltage
10
8
R
L
= 3k
OUTPUT HIGH
V
CC
= 5V
3.00
2.75
DRIVER OUTPUT VOLTAGE (V)
THRESHOLD VOLTAGE (V)
6
4
2
0
–2
–4
–6
–8
–10
–55 –25
OUTPUT LOW
V
CC
= 4.5V
2.25
2.00
1.75
1.50
1.25
1.00
0.75
INPUT LOW
INPUT HIGH
SUPPLY CURRENT (mA)
V
CC
= 4.5V
V
CC
= 5V
50
25
0
75
TEMPERATURE (°C)
Supply Current in Shutdown
150
125
SUPPLY CURRENT (µA)
5
THRESHOLD VOLTAGE (V)
SUPPLY CURRENT (mA)
100
75
50
25
0
–55 –25
50
25
75
0
TEMPERATURE (°C)
ON/OFF Thresholds
3.0
2.5
40
35
SUPPLY CURRENT (mA)
THRESHOLD VOLTAGE (V)
LEAKAGE CURRENT (µA)
2.0
1.5
1.0
ON THRESHOLD
OFF THRESHOLD
0.5
0
–55 –25
50
25
75
0
TEMPERATURE (°C)
4
U W
100
1237 G01
Receiver Input Thresholds
80
70
60
50
40
30
20
10
50
25
0
75
TEMPERATURE (°C)
100
125
Supply Current vs Data Rate
3 DRIVERS ACTIVE
R
L
= 3k
C
L
= 2500pF
2.50
125
0.50
–55 –25
0
0
25
75
50
100
DATA RATE (kBAUD)
125
150
1237 G02
1237 G03
Supply Current in Driver Disable
3.0
2.5
2.0
1.5
1.0
0.5
DRIVER DISABLE Threshold
4
3
2
1
100
125
0
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
0
–55 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1237 G04
1237 G05
1237 G06
Supply Current
100
3 DRIVERS LOADED
R
L
= 3k
Driver Leakage in Shutdown
30
25
20
15
10
5
10
1 DRIVER LOADED
R
L
= 3k
1
V
OUT
= 30V
V
OUT
= –30V
NO LOAD
100
125
0
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
0.1
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1237 G07
1237 G08
1237 G09
LT1237
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Short-Circuit Current
30
SHORT-CIRCUIT CURRENT (mA)
SHORT-CIRCUIT CURRENT (mA)
25
20
15
10
5
0
–55 –25
50
25
75
0
TEMPERATURE (°C)
Receiver Output Waveforms
RX5 OUTPUT
C
L
= 50pF
RX1 TO RX4
OUTPUT
C
L
= 50pF
DRIVER OUTPUT
R
L
= 3k
C
L
= 2500pF
DRIVER OUTPUT
R
L
= 3k
INPUT
INPUT
PI FU CTIO S
V
CC
:
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.
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
60µA 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
≥
1.0µF, 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
≥
0.1µF. See the Applications Infor-
mation section for guidance in choosing filter capacitors
for V
+
and V
–
.
U W
Receiver Short-Circuit Current
50
I
SC+
40
RX1 TO RX4
I
SC–
30
RX1 TO RX4
I
SC+
RX5 I
SC –
I
SC–
20
10
RX5 I
SC+
100
125
0
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1237 G10
1237 G11
Driver Output Waveforms
1237 G12
1237 G13
U
U
U
5
Microcontroller MCU
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