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LTC1387

Single 5V RS232/RS485

Multiprotocol Transceiver

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

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.

ESCRIPTIO

■

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

■

Point-of-Sale Terminals

■

Software Selectable Multiprotocol Interface Ports

■

Low Power RS485/RS422/RS232/EIA562 Interface

■

Cable Repeaters

■

Level Translators

APPLICATIONS

, LTC and LT are registered trademarks of Linear Technology Corporation.

ITY

DR ENABLE

SLEW

1920

CC1

120Ω

LTC1387

LTC1387 • TA01

RECOUT

RS485 INTERFACE

DR IN

LTC1387

RECOUT

DR ENABLE

DR IN

SLEW

120Ω

4000-FT 24-GAUGE TWISTED PAIR

ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE

212019

CC2

Summary of content (12 pages)

PAGE 1
LTC1387 Single 5V RS232/RS485 Multiprotocol Transceiver U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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
PAGE 2
LTC1387 U U RATI GS W W W W AXI U PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VCC) ............................................. 6.5V Input Voltage Drivers ................................... – 0.3V to (VCC + 0.3V) Receivers ............................................. – 25V to 25V 485/232, ON, DXEN RXEN, SLEW ........................... – 0.3V to (VCC + 0.3V) Output Voltage Drivers ................................................. – 18V to 18V Receivers ............................... – 0.
PAGE 3
LTC1387 DC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RS485 Receiver (485/232 = High, ON = RXEN = High) VTH Differential Input Threshold Voltage – 7V ≤ VCM ≤ 12V ∆VTH Input Hysteresis VCM = 0V IIN Input Current (A, B) VIN = 12V VIN = – 7V ● ● – 0.8 – 7V ≤ VIN ≤ 12V ● 12 Input Low Threshold Input High Threshold ● ● 0.8 RIN Input Resistance ● – 0.20 0.
PAGE 4
LTC1387 AC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
PAGE 5
LTC1387 U U U PI FU CTIO S 485/232 (Pin 8): Interface Mode Select Input. A low logic input enables two RS232 drivers and two RS232 receivers. 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.
PAGE 6
LTC1387 U U FU CTIO TABLES Select Modes SELECT INPUTS ON RXEN DXEN RECEIVER 485/232 RXA DRIVER RXB DXY DXZ CHARGE PUMP LOOPBACK COMMENTS 1 0 0 0 Z Z Z Z ON OFF RS232 Mode, DX and RX Off 1 0 1 0 Z Z ON ON ON OFF RS232 Mode, DXY and DXZ On, RX Off 1 1 0 0 ON ON Z Z ON OFF RS232 Mode, DX Off, RXA and RXB On 1 1 1 0 ON ON ON ON ON OFF RS232 Mode, DXY and DXZ On, RXA and RXB On 0 0 1 0 Z Z ON Z ON OFF RS232 Mode, DXY On, DXZ Off, RX Off 0 1 0 0
PAGE 7
LTC1387 W BLOCK DIAGRAM RS232 MODE WITHOUT LOOPBACK 1 20 C1 VDD A B Y Z 485/232 DXEN GND 2 19 3 18 4 17 5 16 6 15 7 14 8 13 9 12 10 11 RS485 MODE WITHOUT LOOPBACK 1 20 C2 C1 VCC RA RB DY DZ ON VDD 2 19 3 18 17 4 A 5 B 15 6 Y DXEN GND VCC VDD 8 13 9 12 10 11 RS485 MODE WITH LOOPBACK 20 2 19 3 18 RA 17 16 RB DY Y 14 485/232* VEE 1 C2 C1 7 Z RXEN 16 RS232 MODE WITH LOOPBACK Z SLEW ON RXEN 485/232 DXEN* VEE GND 6 15 7 14 8 13 9 12 10 11 C
PAGE 8
LTC1387 U W SWITCHI G WAVEFOR S f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE) f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE) 3V 1.5V D 1.5V 0V tPLH tPHL VO 90% Z–Y 50% 10% –VO VDIFF = V(A) – V(B) 90% 50% 10% 1/2 VO tr tf Y VO Z tSKEW tSKEW LTC1387 • F07 Figure 7. RS485 Driver Propagation Delays f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE) f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE) 3V 1.5V DXEN 1.5V 0V tZL tLZ 5V Y, Z 2.
PAGE 9
LTC1387 U W SWITCHI G WAVEFOR S VIH 1.7V 1.3V A, B VIL tPHL tPLH VOH 2.4V R LTC1387 • F11 0.8V VOL Figure 11. RS232 Receiver Propagation Delays 3V 1.5V RXEN f = 1MHz: tr ≤ 10ns: tf ≤ 10ns 1.5V 0V tZL tLZ 5V R 1.5V OUTPUT NORMALLY LOW VOL tZH OUTPUT NORMALLY HIGH VOH 0.5V tHZ 0.5V 1.5V R 0V LTC1387 • F12 Figure 12.
PAGE 10
LTC1387 W U U UO APPLICATI S I FOR ATIO EMI and signal reflection problems. Slow slew rate systems can often use improperly terminated or even unterminated cables with acceptable results. The RS485 differential input receiver features an offset input threshold of – 80mV at 0V common mode voltage. This allows the receiver output to have a known High output state when the inputs are open or shorted. The receiver also features an input hysteresis of 40mV.
PAGE 11
LTC1387 W U U UO APPLICATI S I FOR ATIO LTC1387 RS232 A INTERFACE B RS485 RA A TXD RS232 RA RS485 RXD Y RX RB B RB DY CONTROLLER DY DX DZ/SLEW Z ON DZ VCC RXEN DXEN 485/232 RS232 MODE RS485 TRANSMIT MODE RS485 RECEIVE MODE SHUTDOWN MODE RXEN RXEN = 1 RXEN = 0 RXEN = 1 RXEN = 0 DXEN DXEN = 0 DXEN = 1 DXEN = 0 DXEN = 0 MODE MODE = 0 MODE = 1 MODE = 1 MODE = 0 1387 • F14 Figure 14.
PAGE 12
LTC1387 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. G Package 20-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 6.90 – 7.50* (.272 – .295 ) 5.00 – 5.60** (.197 – .221) 2.0 (.079) 20 19 18 17 16 15 14 13 12 11 1.25 ±0.12 0° – 8° 0.65 (.0256) BSC 0.55 – 0.95 (.022 – .037) 0.09 – 0.25 (.0035 – .010) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 7.40 – 8.20 7.8 – 8.2 (.291 – .323) 5.3 – 5.7 0.05 (.002) 0.