LT1537
Advanced Low Power
5V RS232 Transceiver with
Small Capacitors
FEATURES
s
s
s
s
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
Low Cost
Uses Small Capacitors: 0.1µF, 0.2µF
1
µ
A Supply Current in Shutdown
120kBaud Operation for R
L
= 3k, C
L
= 2500pF
250kBaud Operation for R
L
= 3k, C
L
= 1000pF
CMOS Comparable Low Power: 40mW
Operates from a Single 5V Supply
Easy PC Layout: Flow-through Architecture
Rugged Bipolar Design
Outputs Assume a High Impedance State When Off
or Powered Down
Improved Protection: RS232 I/O Lines Can Be Forced
to
±25V
Without Damage
Output Overvoltage Does Not Force Current Back
into Supplies
Absolutely No Latch-Up
Available in SO Package
The LT
®
1537 is a three-driver, five-receiver RS232 trans-
ceiver, pin compatible with the LT1137A, offering perfor-
mance improvements and two shutdown modes. The
LT1537’s charge pump is designed for extended compli-
ance and can deliver over 35mA of load current. Supply
current is typically 8mA, competitive with similar CMOS
devices. An advanced driver output stage operates up to
250kbaud while driving heavy capacitive loads.
The LT1537 is fully compliant with all RS232 specifica-
tions. Special bipolar construction techniques protect the
drivers and receivers beyond the fault conditions stipu-
lated for RS232. Driver outputs and receiver inputs can be
shorted to
±25V
without damaging the device or the
power supply generator. In addition, the RS232 I/O pins
are resilient to multiple
±5kV
ESD strikes.
The transceiver has two shutdown modes. One mode
disables the drivers and the charge pump, the other shuts
down all circuitry. While shut down, the drivers and
receivers assume high impedance output states.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATI
s
s
S
Notebook Computers
Palmtop Computers
TYPICAL APPLICATI
+
0.1µF
2
×
0.1µF
V
+
5V V
CC
1
2
3
4
DRIVER OUT
RX IN
DRIVER OUT
TO
LINE
RX IN
RX IN
RX IN
DRIVER OUT
RX IN
ON/OFF = 5V
5
6
7
8
9
10
11
12
13
14
LT1537
28
27
25
24
23
22
21
20
19
18
17
16
15
26
V
–
0.1µF
RECEIVER
OUTPUT
C
L
= 50pF
R
DRIVER
OUTPUT
R
L
= 3k
C
L
= 2500pF
DRIVER IN
RX OUT
DRIVER IN
RX OUT
RX OUT
RX OUT
DRIVER IN
RX OUT
GND
DRIVER
DISABLE
LT1537 • TA01
+
+
2
×
0.1µF
TO LOGIC
INPUT
U
Output Waveforms
LT1537 • TA02
+
UO
UO
1
LT1537
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
+
1
5V V
CC
2
C1
+
3
C1
–
4
DRIVER OUT 5
RX IN 6
DRIVER OUT 7
RX IN 8
RX IN 9
RX IN 10
DRIVER OUT 11
RX IN 12
ON/OFF 13
NC 14
G PACKAGE
28-LEAD PLASTIC SSOP
28 V
–
27 C2
–
26 C2
+
25 DRIVER IN
24 RX OUT
23 DRIVER IN
22 RX OUT
21 RX OUT
20 RX OUT
19 DRIVER IN
18 RX OUT
17 GND
16 DRIVER
DISABLE
15 NC
SW PACKAGE
28-LEAD PLASTIC SO WIDE
Supply Voltage (V
CC
) ............................................. 5.5V
V
+
........................................................................ 13.2V
V
–
(Note 7) .......................................................... – 6.5V
Input Voltage
Driver ........................................................... V
–
to V
+
Receiver ............................................... – 25V to 25V
Output Voltage
Driver ....................................... V
+
– 25V to V
–
+ 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
LT1537C ................................................. 0°C to 70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT1537CG
LT1537CSW
T
JMAX
= 150°C,
θ
JA
= 96°C/ W (G)
T
JMAX
= 150°C,
θ
JA
= 85°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
)
Shutdown to Turn-On
ON/OFF Pin Thresholds
ON/OFF Pin Current
Driver Disable Pin Thresholds
Driver Disable Pin Current
Oscillator Frequency
Any Driver
Output Voltage Swing
Logic Input Voltage Level
Logic Input Current
Output Short-Circuit Current
CONDITIONS
(Note 2)
MIN
TYP
8.6
– 7.0
8
1.0
1.5
0.2
1.4
1.4
1.4
1.4
130
MAX
UNITS
V
V
mA
µA
mA
ms
V
V
µA
V
V
µA
kHz
V
V
V
µA
mA
(Note 3)
Shutdown (Note 4)
DRIVER DISABLE
C
+
, C
–
= 0.1µF, C1, C2 = 0.2µF
Input LOW Level (Device Shutdown)
Input HIGH Level (Device Enabled)
0V
≤
V
ON/OFF
≤
5V
Input LOW Level (Drivers Enabled)
Input HIGH Level (Drivers Disabled)
0V
≤
V
DRIVER DISABLE
≤
5V
q
q
17
10
q
q
q
q
q
q
0.8
80
0.8
500
2.4
–15
2.4
–10
Load = 3k to GND
Input LOW Level (V
OUT
= HIGH)
Input HIGH Level (V
OUT
= LOW)
0.8V
≤
V
IN
≤
2V
V
OUT
= 0V
Positive
Negative
q
q
q
q
q
5.0
2
7.5
– 6.3
1.4
1.4
5
±17
– 5.0
0.8
20
2
U
W
U
U
W W
W
LT1537
ELECTRICAL CHARACTERISTICS
PARAMETER
Any Driver
Output Leakage Current
Data Rate
Slew Rate
Propagation Delay
Any Receiver
Input Voltage Thresholds
Hysteresis
Input Resistance
Output Voltage
Output Leakage Current
Output Short-Circuit Current
Propagation Delay
CONDITIONS
(Note 2)
MIN
q
TYP
10
MAX
100
UNITS
µA
kBaud
kBaud
V/µs
V/µs
µs
µs
V
V
V
kΩ
V
V
µA
mA
mA
ns
ns
Shutdown V
OUT
=
±15V
(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)
V
IN
=
±10V
Output LOW, I
OUT
= – 1.6mA
Output HIGH, I
OUT
= 160µA (V
CC
= 5V)
Shutdown (Note 4) 0
≤
V
OUT
≤
V
CC
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
120
250
4
15
15
0.6
0.5
1.3
1.7
0.4
5
0.2
4.2
1
– 20
20
250
350
30
1.3
1.3
q
q
q
q
q
q
0.8
0.1
3
3.5
2.4
1.0
7
0.4
10
– 10
600
600
10
The
q
denotes specifications which apply over the 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:
Testing done at V
CC
= 5V and V
ON/OFF
= 3V. C1 = C2 = 0.2µF,
C
+
= C
–
= 0.1µF.
Note 3:
Supply current is measured with driver and receiver outputs
unloaded and the driver inputs tied high.
Note 4:
Supply current and leakage current 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:
Absolute maximum externally applied voltage. Internal charge
pump may force a larger value on this pin.
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output Voltage
10
8
OUTPUT HIGH
3.00
2.75
THRESHOLD VOLTAGE (V)
DRIVER OUTPUT VOLTAGE (V)
6
4
2
0
–2
–4
–6
–8
–10
–50 –25
OUTPUT LOW
50
25
0
75
TEMPERATURE (°C)
R
L
= 3k
100
125
V
CC
= 5V
V
CC
= 5.5V
V
CC
= 4.5V
V
CC
= 5.5V
V
CC
= 5V
V
CC
= 4.5V
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
INPUT LOW
INPUT HIGH
SUPPLY CURRENT (mA)
U W
LT1537 • TPC01
Receiver Input Thresholds
80
70
60
50
40
30
20
10
0
Supply Current vs Data Rate
3 DRIVERS ACTIVE
R
L
= 3k
C
L
= 2500pF
2.50
0
25
100
75
DATA RATE (kBAUD)
50
125
150
ILT1537 • TPC02
LTX1537 • TPC03
3
LT1537
TYPICAL PERFOR A CE CHARACTERISTICS
Positive Supply Output
Compliance Curve
10
NEGATIVE SUPPLY OUTPUT (V)
POSITIVE SUPPLY OUTPUT (V)
THRESHOLD VOLTAGE (V)
8
6
4
2
0
0
5
10
POSITIVE LOAD CURRENT (mA)
On/Off Thresholds
3.0
2.5
THRESHOLD VOLTAGE (V)
LEAKAGE CURRENT (µA)
SUPPLY VOLTAGE (mA)
2.0
ON THRESHOLD
1.5
1.0
OFF THRESHOLD
0.5
0
–55
–25
75
0
25
50
TEMPERATURE (°C)
Driver Output Short-Circuit Current
30
30
I
SC+
SHORT-CIRCUIT CURRENT (mA)
SHORT-CIRCUIT CURRENT (mA)
25
20
I
SC
15
10
5
0
–55 –25
–
50
25
75
0
TEMPERATURE (°C)
4
U W
15
LT1537 • TPC04
Negative Supply Output
Compliance Curve
–10
Driver Disable Threshold
3.0
2.5
2.0
1.5
1.0
0.5
0
–55
–8
–6
–4
–2
0
0
5
10
NEGATIVE LOAD CURRENT (mA)
15
–25
75
0
25
50
TEMPERATURE (°C)
100
125
LT1537 • TPC05
LT1537 • TPC06
Supply Current
40
20kBAUD
35
30
25
20
15
10
5
0
–55
–25
0
50
75
25
TEMPERATURE (°C)
100
125
3 DRIVERS LOADED R
L
= 3k
2 DRIVERS LOADED R
L
= 3k
1 DRIVERS LOADED R
L
= 3k
NO LOAD
100
Driver Leakage in Shutdown
10
1
V
OUT
= 15V
V
OUT
= –15V
100
125
0.1
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
LT1537 • TPC07
LT1537 • TPC08
LT1537 • TPC09
Receiver Short-Circuit Current
25
20
15
I
SC–
10
5
0
–55 –25
I
SC+
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
LT1537 • TPC10
LT1537 • TPC11
LT1537
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown to Driver Output
DRIVER
OUTPUT HIGH
R
L
= 3k
10
5
0
DRIVER – 5
OUTPUT LOW
R
L
= 3k – 10
ON/OFF PIN
DRIVER OUTPUT
R
L
= 3k
C
L
= 2500pF
DRIVER OUTPUT
R
L
= 3k
PI FU CTIO S
V
CC
:
5V Input Supply Pin. Supply current drops to zero in
the shutdown mode. This pin should be decoupled with a
0.1µF ceramic capacitor close to the package pin. Insuffi-
cient 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 shutdown mode which
reduces input supply current to zero and places all of the
drivers and receivers in high impedance state. 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 drivers
in a high impedance state. 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 1.5mA 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
≥
0.1µF, tied to ground or V
CC
. Larger value capaci-
tors may be used to reduce supply ripple. With multiple
transceivers, the V
+
and V
–
pins may be paralleled into
common capacitors. For large numbers of transceivers,
increasing the size of the shared common storage capaci-
tors is recommended to reduce ripple.
V
–
:
Negative Supply Output (RS232 Drivers). V
–
≈
–(2V
CC
– 2.5V). This pin requires an external charge
storage capacitor C
≥
0.1µF. V
–
is short-circuit proof for
30 seconds.
C1
+
, C1
–
, C2
+
, C2
–
:
Commutating Capacitor Inputs. These
pins require two external capacitors C
≥
0.2µF: one from
C1
+
to C1
–
and another from C2
+
to C2
–
. To maintain
charge pump efficiency, the capacitor’s effective series
resistance should be less than 2Ω. Low ESR ceramic
capacitors work well in this application.
DRIVER IN:
RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Inputs should not be allowed to
float. Tie unused inputs to V
CC
.
DRIVER OUT:
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 in
shutdown mode, V
CC
= 0V or when the driver disable pin
is active. Outputs are fully short-circuit protected from V
–
+ 25V to V
+
– 25V. Applying higher voltages will not
damage the device if the overdrive 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
±5kV
for human body model discharges.
U W
Driver Output Waveforms
INPUT
LT1537 • TPC12
LT1537 • TPC13
U
U
U
5
PCB Design
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