LTC1387
Single 5V RS232/RS485
Multiprotocol Transceiver
FEATURES
s
s
s
DESCRIPTIO
s
s
s
s
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Two RS232 Transceivers or One RS485 Transceiver
Operates from a Single 5V Supply
Guaranteed Receiver Output with Inputs
Floating or Shorted to Ground
Logic Selectable Fast/Slow RS485 Driver Slew Rate
Low Supply Current: 7mA Typical
5µA Supply Current in Shutdown
Self-Testing Capability in Loopback Mode
Separate Driver and Receiver Enable Controls
Driver Maintains High Impedance in Three-State,
Shutdown or with Power Off
Receiver Inputs Can Withstand
±25V
The LTC
®
1387 is a low power reconfigurable CMOS bidi-
rectional transceiver. It can be configured as an RS485
differential port or as two RS232 single-ended ports. An
onboard charge pump uses four 0.1µF capacitors to
generate boosted positive and negative supplies, allowing
the RS232 drivers to meet
±5V
output swing require-
ments with only a single 5V supply. A shutdown mode
reduces the I
CC
supply current to 5µA.
The RS232 transceivers are in full compliance with RS232
specification. The RS485 transceiver is in full compliance
with RS485 and RS422 specifications. The RS485 re-
ceiver assumes a known output state when the inputs are
floating or shorted to ground. All interface drivers feature
short-circuit and thermal shutdown protection. An enable
pin allows RS485 driver outputs to be forced into high
impedance which is maintained even when the outputs are
forced beyond supply rails or the power is off. A loop back
mode allows the driver outputs to be connected back to the
receiver inputs for diagnostic self-test.
The LTC1387 is available in 20-pin plastic SSOP and SW
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIONS
s
s
s
s
s
Point-of-Sale Terminals
Software Selectable Multiprotocol Interface Ports
Low Power RS485/RS422/RS232/EIA562 Interface
Cable Repeaters
Level Translators
TYPICAL APPLICATI
2
3
1 20
LTC1387
19
V
CC1
5V
18
RECOUT
17
4
5
120Ω
6
7
8
13
10
RS485 INTERFACE
120Ω
4
5
6
7
8
13
10
DR IN
SLEW
DR ENABLE
5V
15
14
9
12
11
4000-FT 24-GAUGE TWISTED PAIR
5V
5V
5V
5V
ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE
LTC1387 • TA01
U
19
20 1
LTC1387
2
3
18
V
CC2
5V
17
RECOUT
15
14
9
12
11
DR IN
SLEW
DR ENABLE
5V
UO
U
1
LTC1387
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
C1
+
1
C1
–
2
V
DD
3
A 4
B 5
Y 6
Z 7
485/232 8
DXEN 9
GND 10
G PACKAGE
20-LEAD PLASTIC SSOP
20 C2
+
19 C2
–
18 V
CC
17 R
A
16 R
B
15 D
Y
14 D
Z
/SLEW
13 ON
12 RXEN
11 V
EE
SW PACKAGE
20-LEAD PLASTIC SO
Supply Voltage (V
CC
) ............................................. 6.5V
Input Voltage
Drivers ................................... – 0.3V to (V
CC
+ 0.3V)
Receivers ............................................. – 25V to 25V
485/232, ON, DXEN
RXEN, SLEW ........................... – 0.3V to (V
CC
+ 0.3V)
Output Voltage
Drivers ................................................. – 18V to 18V
Receivers ............................... – 0.3V to (V
CC
+ 0.3V)
Short-Circuit Duration
Output ........................................................ Indefinite
V
DD
, V
EE
, C1
+
, C1
–
, C2
+
, C2
–
.......................... 30 sec
Operating Temperature Range
LTC1387C .............................................. 0°C to 70°C
LTC1387I ........................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER PART
NUMBER
LTC1387CG
LTC1387CSW
LTC1387IG
LTC1387ISW
T
JMAX
= 125°C,
θ
JA
= 120°C/W (G)
T
JMAX
= 125°C,
θ
JA
= 75°C/W (SW)
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
OD1
V
OD2
∆V
OD
V
OC
∆V
OC
I
OSD
I
OZD
V
O
I
OSD
V
IH
V
IL
I
IN
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (With Load)
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
Driver Common Mode Output Voltage
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
Driver Short-Circuit Current
Three-State Output Current (Y, Z)
Output Voltage Swing
Output Short-Circuit Current
Input High Voltage
Input Low Voltage
Input Current
RS485 Driver (485/232 = High, ON = DXEN = High)
I
O
= 0
T
A
= 25°C, V
CC
= 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
CONDITIONS
q
q
q
q
q
q
q
q
MIN
TYP
MAX
6
UNITS
V
V
V
V
V
V
mA
mA
µA
V
V
Figure 1, R = 50Ω (RS422)
Figure 1, R = 27Ω (RS485)
Figure 1, R = 27Ω or R = 50Ω
Figure 1, R = 27Ω or R = 50Ω
Figure 1, R = 27Ω or R = 50Ω
V
O
= – 7V, 12V; V
O
= High
V
O
= – 7V, 12V; V
O
= Low (Note 4)
– 7V
≤
V
O
≤
12V
Figure 4, R
L
= 3k, Positive
Figure 4, R
L
= 3k, Negative
V
O
= 0V
D
Y
, D
Z
, DXEN, RXEN, ON, 485/232, SLEW
D
Y
, D
Z
, DXEN, RXEN, ON, 485/232, SLEW
D
Y
, D
Z
, DXEN, RXEN, ON, 485/232
SLEW (Note 5)
2.0
1.5
6
6
0.2
3
0.2
35
10
±5
250
250
500
RS232 Driver (485/232 = Low, ON = DXEN = High)
q
q
q
5
–5
6.5
– 6.5
±17
±60
Driver Inputs and Control Inputs
q
q
q
q
2
0.8
±0.1
5
±10
15
2
U
mA
V
V
µA
µA
W
U
U
W W
W
LTC1387
DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
TH
∆V
TH
I
IN
R
IN
V
TH
∆V
TH
R
IN
V
OH
V
OL
I
OSR
I
OZR
V
DD
V
EE
PARAMETER
Differential Input Threshold Voltage
Input Hysteresis
Input Current (A, B)
Input Resistance
Receiver Input Voltage Threshold
Receiver Input Hysteresis
Receiver Input Resistance
Receiver Output High Voltage
Receiver Output Low Voltage
Short-Circuit Current
Three-State Output Current
V
DD
Output Voltage
V
EE
Output Voltage
RS485 Receiver (485/232 = High, ON = RXEN = High)
T
A
= 25°C, V
CC
= 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
CONDITIONS
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
V
IN
= 12V
V
IN
= – 7V
– 7V
≤
V
IN
≤
12V
Input Low Threshold
Input High Threshold
V
IN
=
±10V
I
O
= – 3mA, V
IN
= 0V, 485/232 = Low
I
O
= 3mA, V
IN
= 3V, 485/232 = Low
0V
≤
V
O
≤
V
CC
RXEN = 0V
No Load, ON = DXEN = RXEN = High
I
DD
= – 5mA, ON = DXEN = RXEN = High
No Load, ON = DXEN = RXEN = High
I
EE
= 5mA, ON = DXEN = RXEN = High
No Load, ON = DXEN = RXEN = High
Shutdown, ON = DXEN = RXEN = 0V
q
q
q
q
q
q
q
q
q
q
MIN
– 0.20
TYP
MAX
0.20
UNITS
V
mV
mA
mA
kΩ
V
V
V
kΩ
V
40
1
– 0.8
12
0.8
2.4
0.6
3
3.5
7
±0.1
8
7
– 7.7
– 7.0
7
5
25
100
5
4.6
0.2
0.4
85
±10
7
24
RS232 Receiver (485/232 = Low, ON = RXEN = High)
q
q
Receiver Output (ON = RXEN = High)
V
mA
µA
V
V
V
V
mA
µA
Power Supply Generator
Power Supply
I
CC
V
CC
Supply Current
AC ELECTRICAL CHARACTERISTICS
SYMBOL
SR
t
T
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
SKEW
t
r
, t
f
PARAMETER
Slew Rate
Transition Time
Driver Input to Output
Driver Input to Output
Receiver Input to Output
Receiver Input to Output
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
RS232 Mode (ON = DXEN = RXEN = High, 485/232 = Low)
T
A
= 25°C, V
CC
= 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
CONDITIONS
Figure 4, R
L
= 3k, C
L
= 15pF
Figure 4, R
L
= 3k, C
L
= 1000pF
Figure 4, R
L
= 3k, C
L
= 2500pF
Figures 4, 10, R
L
= 3k, C
L
= 15pF
Figures 4, 10, R
L
= 3k, C
L
= 15pF
Figures 5, 11
Figures 5, 11
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
q
q
q
q
q
q
q
MIN
TYP
MAX
30
UNITS
V/µs
V/µs
µs
µs
µs
µs
µs
ns
ns
ns
ns
4
0.22
1.9
0.6
0.6
0.3
0.4
15
15
3
40
40
5
15
3.1
4
4
6
6
70
70
15
40
RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High)
q
q
q
q
3
LTC1387
AC ELECTRICAL CHARACTERISTICS
SYMBOL
t
ZL
t
ZH
t
LZ
t
HZ
t
PLH
t
PHL
t
SKEW
t
r
, t
f
t
ZL
t
ZH
t
LZ
t
HZ
t
PLH
t
PHL
t
SKEW
t
ZL
t
ZH
t
LZ
t
HZ
PARAMETER
Driver Enable to Output Low
Driver Enable to Output High
Driver Disable from Low
Driver Disable from High
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Driver Enable to Output Low
Driver Enable to Output High
Driver Disable from Low
Driver Disable from High
Receiver Input to Output
Receiver Input to Output
Differential Receiver Skew,
t
PLH
– t
PHL
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
T
A
= 25°C, V
CC
= 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
CONDITIONS
Figures 3, 8, C
L
= 100pF, S1 Closed
Figures 3, 8, C
L
= 100pF, S2 Closed
Figures 3, 8, C
L
= 15pF, S1 Closed
Figures 3, 8, C
L
= 15pF, S2 Closed
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 2, 7, R
L
= 54Ω, C
L
= 100pF
Figures 3, 8, C
L
= 100pF, S1 Closed
Figures 3, 8, C
L
= 100pF, S2 Closed
Figures 3, 8, C
L
= 15pF, S1 Closed
Figures 3, 8, C
L
= 15pF, S2 Closed
Figures 2, 9, R
L
= 54Ω, C
L
= 100pF
Figures 2, 9, R
L
= 54Ω, C
L
= 100pF
Figures 2, 9, R
L
= 54Ω, C
L
= 100pF
Figures 6, 12, C
L
= 15pF, S1 Closed
Figures 6, 12, C
L
= 15pF, S2 Closed
Figures 6, 12, C
L
= 15pF, S1 Closed
Figures 6, 12, C
L
= 15pF, S2 Closed
q
q
q
q
q
q
q
q
MIN
TYP
50
50
50
60
MAX
90
90
90
90
1500
1500
750
1500
1500
1500
200
200
140
140
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High)
RS485 Mode (Slow Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = Low)
q
q
q
q
q
q
q
q
100
100
150
700
700
200
300
600
600
100
100
RS485 Mode (ON = RXEN = High, 485/232 = High)
q
q
20
20
70
70
10
40
40
40
40
Receiver Output Enable/Disable (ON = High)
90
90
90
90
ns
ns
ns
ns
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 3:
All typicals are given at V
CC
= 5V, C1 = C2 = C3 = C4 = 0.1µF
and T
A
= 25°C.
Note 4:
Short-circuit current for RS485 driver output low state folds back
above V
CC
. Peak current occurs around V
O
= 3V.
Note 5:
SLEW includes an internal pull-up in RS485 mode.
PIN FUNCTIONS
C1
+
(Pin 1):
Commutating Capacitor C1 Positive Terminal.
Requires an external 0.1µF capacitor between Pins 1 and 2.
C1
–
(Pin 2):
Commutating Capacitor C1 Negative Terminal.
V
DD
(Pin 3):
Charge Pump Positive Supply Output.
Requires an external 0.1µF capacitor to ground.
A (Pin 4):
Receiver Input A. Inverting input of RS232
receiver A in RS232 mode; inverting RS485 receiver input
in RS485 mode.
B (Pin 5):
Receiver Input B. Inverting input of RS232
receiver B in RS232 mode; noninverting RS485 receiver
input in RS485 mode.
Y (Pin 6):
Driver Output Y. Inverting RS232 driver Y output
in RS232 mode; inverting RS485 driver output in RS485
mode.
Z (Pin 7):
Driver Output Z. Inverting RS232 driver Z output
in RS232 mode; noninverting RS485 driver output in
RS485 mode.
4
U
U
U
LTC1387
PI FU CTIO S
485/232 (Pin 8):
Interface Mode Select Input. A low logic
input enables two RS232 drivers and two RS232 receiv-
ers. A high input enables the RS485 driver and the RS485
receiver.
DXEN (Pin 9):
Driver Enable Input. A high logic input
enables the drivers and a low logic input disables the
drivers. When disabled, all driver outputs are in high
impedance
GND (Pin 10):
Ground.
V
EE
(Pin 11):
Charge Pump Negative Supply Output.
Requires an external 0.1µF capacitor to ground.
RXEN (Pin 12):
Receiver Enable Input. A high logic input
enables the receivers and a low logic input disables the
receivers. When disabled, all receiver outputs are in high
impedance.
ON (Pin 13):
A high logic level at ON input keeps the charge
pump active regardless of the state of the DXEN and RXEN
inputs. When the charge pump is active, the drivers and
receivers can be enabled or disabled without waiting for
charge pump stabilization time (typically 100µs with 0.1µF
capacitors). A low logic state at the ON, DXEN and RXEN
inputs will put the transceiver and charge pump in shut-
down mode and reduces I
CC
to 5µA. Whenever the trans-
ceiver is activated from shutdown, the charge pump
should be allowed to stabilize before data transmission.
When DXEN and RXEN are high and ON is low, the charge
pump, drivers and receivers are all active and the driver
outputs are internally looped back to the inputs of the
receiver. The three control inputs ON, DXEN and RXEN can
be configured for one-, two- or three-wire control: one-
wire mode – all three inputs connected together; two-wire
mode – inputs ON and RXEN connected to one wire, DXEN
a separate wire; three-wire mode – separate wires to each
input. See the Function Tables.
D
Z
/SLEW (Pin 14):
Driver Z or Slew Input. In RS232
mode, this pin is the driver Z input. In RS485 mode, this
pin controls the slew rate of the RS485 driver. With the
SLEW pin high, the RS485 driver runs at maximum (fast)
slew rate and can transmit signals up to 5MBd. With the
SLEW pin low, the RS485 driver runs with reduced (slow)
slew rate to control reflections with improperly terminated
cables. In slow mode, the RS485 driver can support data
rates up to 150kBd. This SLEW pin has internal 5µA pull-
up during RS485 mode.
D
Y
(Pin 15):
Driver Y Input. Input Y in RS232 mode; the
differential driver input in RS485 mode.
R
B
(Pin 16):
Receiver B Output. Output B in RS232 mode;
output is high impedance in RS485 mode.
R
A
(Pin 17):
Receiver A Output. Output A in RS232 mode;
the differential receiver output in RS485 mode.
V
CC
(Pin 18):
Positive Supply. 4.75V
≤
V
CC
≤
5.25V.
Requires an external 0.1µF bypass capacitor to ground.
C2
–
(Pin 19):
Commutating Capacitor C2 Negative Termi-
nal. Requires an external 0.1µF capacitor between Pins 19
and 20.
C2
+
(Pin 20):
Commutating Capacitor C2 Positive
Terminal.
U
U
U
5
Embedded System
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