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PDF LTC1387IG Data sheet ( Hoja de datos )
| Número de pieza | LTC1387IG | |
| Descripción | Single 5V RS232/RS485 Multiprotocol Transceiver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1387
Single 5V RS232/RS485
Multiprotocol Transceiver
FEATURES
s Two RS232 Transceivers or One RS485 Transceiver
s Operates from a Single 5V Supply
s Guaranteed Receiver Output with Inputs
Floating or Shorted to Ground
s Logic Selectable Fast/Slow RS485 Driver Slew Rate
s Low Supply Current: 7mA Typical
s 5µA Supply Current in Shutdown
s Self-Testing Capability in Loopback Mode
s Separate Driver and Receiver Enable Controls
s Driver Maintains High Impedance in Three-State,
Shutdown or with Power Off
s Receiver Inputs Can Withstand ±25V
U
APPLICATIONS
s Point-of-Sale Terminals
s Software Selectable Multiprotocol Interface Ports
s Low Power RS485/RS422/RS232/EIA562 Interface
s Cable Repeaters
s Level Translators
DESCRIPTIO
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 ICC 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.
TYPICAL APPLICATI
VCC1
5V
2 1 20 19
3
LTC1387
18
19 20 1 2
3
LTC1387
18
VCC2
5V
17
RECOUT
DR IN
SLEW
DR ENABLE
5V
15
14
9
12
11
4
5 RS485 INTERFACE
120Ω
6
120Ω
7 4000-FT 24-GAUGE TWISTED PAIR
4
5
6
7
8 5V
13 5V
10
8
5V
5V 13
10
ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE
17
RECOUT
15
DR IN
14 SLEW
9 DR ENABLE
12 5V
11
LTC1387 • TA01
1
1 page  
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.
VEE (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 ICC 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.
DZ/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.
DY (Pin 15): Driver Y Input. Input Y in RS232 mode; the
differential driver input in RS485 mode.
RB (Pin 16): Receiver B Output. Output B in RS232 mode;
output is high impedance in RS485 mode.
RA (Pin 17): Receiver A Output. Output A in RS232 mode;
the differential receiver output in RS485 mode.
VCC (Pin 18): Positive Supply. 4.75V ≤ VCC ≤ 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.
5
5 Page 
LTC1387
APPLICATI S I FOR ATIO
A
INTERFACE
B
RS232
TXD
RS232
RXD
RS485
RS485
A
B
Y
Z
LTC1387
RA
RB
DY
DZ
RA
RB
DY
DZ/SLEW VCC
ON
RXEN
DXEN
485/232
RX
CONTROLLER
DX
RXEN
DXEN
MODE
RS232
MODE
RXEN = 1
DXEN = 0
MODE = 0
RS485
TRANSMIT MODE
RXEN = 0
DXEN = 1
MODE = 1
RS485
RECEIVE MODE
RXEN = 1
DXEN = 0
MODE = 1
Figure 14. Full-Duplex RS232 (1-Channel), Half-Duplex RS485
SHUTDOWN
MODE
RXEN = 0
DXEN = 0
MODE = 0
1387 • F14
RS232 RS485
A
RXD
RS485
B
INTERFACE RS232 RS485
Y
TXD
RS485
Z
A
B
Y
Z
LTC1387
RA
RB
DY
DZ
RA
RB
DY
DZ/SLEW VCC
ON
RXEN
DXEN
485/232
RX
CONTROLLER
DX
RXEN
DXEN
MODE
RS232
MODE
RXEN = 1
DXEN = 1
MODE = 0
RS485
MODE
RXEN = 1
DXEN = 1
MODE = 1
Figure 15. Full-Duplex RS232 (1-Channel), Full-Duplex RS485/RS422
SHUTDOWN
MODE
RXEN = 0
DXEN = 0
MODE = X
1387 • F15
RS232 RS485
A
RXD
B
INTERFACE
Y
RS232
CTS
RS232
TXD
RS485
RS485
RS232 RS485
Z
RTS
A
B
Y
Z
LTC1387
RA
RB
DY
DZ
RA
RB
DY
DZ/SLEW
ON
RXEN
DXEN
485/232
RX1
RX2
CONTROLLER
DX1
DX2/SLEW
ON
RXEN
DXEN
MODE
RS232
MODE
ON = 1
RXEN = 1
DXEN = 1
MODE = 0
RS485
MODE
ON = 1
RXEN = 1
DXEN = 1
MODE = 1
SHUTDOWN
MODE
ON = 0
RXEN = 0
DXEN = 0
MODE = X
1387 • F16
Figure 16. Full-Duplex RS232 (2-Channel), Full-Duplex RS485/RS422 with SLEW Control
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC1387IG.PDF ] | |
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