1

LTC1387Single 5V RS232/RS485

Multiprotocol Transceiver

SFEATUREThe LTC®1387 is a low power reconfigurable CMOS bidi-rectional transceiver. It can be configured as an RS485differential port or as two RS232 single-ended ports. Anonboard charge pump uses four 0.1µF capacitors togenerate boosted positive and negative supplies, allowingthe RS232 drivers to meet ±5V output swing require-ments with only a single 5V supply. A shutdown modereduces the ICC supply current to 5µA.

The RS232 transceivers are in full compliance with RS232specification. The RS485 transceiver is in full compliancewith RS485 and RS422 specifications. The RS485 re-ceiver assumes a known output state when the inputs arefloating or shorted to ground. All interface drivers featureshort-circuit and thermal shutdown protection. An enablepin allows RS485 driver outputs to be forced into highimpedance which is maintained even when the outputs areforced beyond supply rails or the power is off. A loop backmode allows the driver outputs to be connected back to thereceiver inputs for diagnostic self-test.

The LTC1387 is available in 20-pin plastic SSOP and SWpackages.

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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

APPLICATIONSU

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

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PPLICATITYPICAL

9DR ENABLE

14SLEW

8 5V13

5V12 5V

18

3

18

31920

VCC15V

120Ω

4

LTC1387

LTC1387 • TA01

RECOUT RS485 INTERFACE5

6

7

10

17

DR IN15

11

4

9

LTC1387

RECOUT

15

DR ENABLE

DR IN

5

6

7

8

13

10

17

SLEW14

5V12

11

120Ω

4000-FT 24-GAUGE TWISTED PAIR

5V

5V

ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE

12 212019

VCC25V

2

LTC1387

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ARBSOLUTE XI TI S

ORDER PARTNUMBER

(Note 1)Supply Voltage (VCC) ............................................. 6.5VInput Voltage

Drivers ................................... –0.3V to (VCC + 0.3V)Receivers ............................................. –25V to 25V485/232, ON, DXENRXEN, SLEW ........................... –0.3V to (VCC + 0.3V)

Output VoltageDrivers ................................................. –18V to 18VReceivers ............................... –0.3V to (VCC + 0.3V)

Short-Circuit DurationOutput ........................................................ IndefiniteVDD, VEE, C1+, C1–, C2+, C2– .......................... 30 sec

Operating Temperature RangeLTC1387C .............................................. 0°C to 70°CLTC1387I ........................................... –40°C to 85°C

Storage Temperature Range ................ –65°C to 150°CLead Temperature (Soldering, 10 sec)................ 300°C

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PACKAGE/ORDER I FOR ATIO

Consult factory for Military grade parts.

TJMAX = 125°C, θJA = 120°C/W (G)TJMAX = 125°C, θJA = 75°C/W (SW)

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TOP VIEW

SW PACKAGE20-LEAD PLASTIC SO

G PACKAGE20-LEAD PLASTIC SSOP

20

19

18

17

16

15

14

13

12

11

C1+

C1–

VDD

A

B

Y

Z

485/232

DXEN

GND

C2+

C2–

VCC

RA

RB

DY

DZ/SLEW

ON

RXEN

VEE

DC ELECTRICAL CHARACTERISTICS

LTC1387CGLTC1387CSWLTC1387IGLTC1387ISW

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 Driver (485/232 = High, ON = DXEN = High)

VOD1 Differential Driver Output Voltage (Unloaded) IO = 0 6 V

VOD2 Differential Driver Output Voltage (With Load) Figure 1, R = 50Ω (RS422) 2.0 6 VFigure 1, R = 27Ω (RS485) 1.5 6 V

∆VOD Change in Magnitude of Driver Differential Figure 1, R = 27Ω or R = 50Ω 0.2 VOutput Voltage for Complementary Output States

VOC Driver Common Mode Output Voltage Figure 1, R = 27Ω or R = 50Ω 3 V

∆VOC Change in Magnitude of Driver Common Mode Figure 1, R = 27Ω or R = 50Ω 0.2 VOutput Voltage for Complementary Output States

IOSD Driver Short-Circuit Current VO = –7V, 12V; VO = High 35 250 mAVO = –7V, 12V; VO = Low (Note 4) 10 250 mA

IOZD Three-State Output Current (Y, Z) –7V ≤ VO ≤ 12V ±5 500 µA

RS232 Driver (485/232 = Low, ON = DXEN = High)

VO Output Voltage Swing Figure 4, RL = 3k, Positive 5 6.5 VFigure 4, RL = 3k, Negative –5 –6.5 V

IOSD Output Short-Circuit Current VO = 0V ±17 ±60 mA

Driver Inputs and Control Inputs

VIH Input High Voltage DY, DZ, DXEN, RXEN, ON, 485/232, SLEW 2 V

VIL Input Low Voltage DY, DZ, DXEN, RXEN, ON, 485/232, SLEW 0.8 V

IIN Input Current DY, DZ, DXEN, RXEN, ON, 485/232 ±0.1 ±10 µASLEW (Note 5) 5 15 µA

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LTC1387

DC ELECTRICAL CHARACTERISTICSTA = 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 – 0.20 0.20 V

∆VTH Input Hysteresis VCM = 0V 40 mV

IIN Input Current (A, B) VIN = 12V 1 mAVIN = –7V –0.8 mA

RIN Input Resistance –7V ≤ VIN ≤ 12V 12 24 kΩRS232 Receiver (485/232 = Low, ON = RXEN = High)

VTH Receiver Input Voltage Threshold Input Low Threshold 0.8 VInput High Threshold 2.4 V

∆VTH Receiver Input Hysteresis 0.6 V

RIN Receiver Input Resistance VIN = ±10V 3 5 7 kΩReceiver Output (ON = RXEN = High)

VOH Receiver Output High Voltage IO = –3mA, VIN = 0V, 485/232 = Low 3.5 4.6 V

VOL Receiver Output Low Voltage IO = 3mA, VIN = 3V, 485/232 = Low 0.2 0.4 V

IOSR Short-Circuit Current 0V ≤ VO ≤ VCC 7 85 mA

IOZR Three-State Output Current RXEN = 0V ±0.1 ±10 µA

Power Supply Generator

VDD VDD Output Voltage No Load, ON = DXEN = RXEN = High 8 VIDD = –5mA, ON = DXEN = RXEN = High 7 V

VEE VEE Output Voltage No Load, ON = DXEN = RXEN = High –7.7 VIEE = 5mA, ON = DXEN = RXEN = High –7.0 V

Power Supply

ICC VCC Supply Current No Load, ON = DXEN = RXEN = High 7 25 mAShutdown, ON = DXEN = RXEN = 0V 5 100 µA

AC ELECTRICAL CHARACTERISTICSTA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

RS232 Mode (ON = DXEN = RXEN = High, 485/232 = Low)

SR Slew Rate Figure 4, RL = 3k, CL = 15pF 30 V/µsFigure 4, RL = 3k, CL = 1000pF 4 V/µs

tT Transition Time Figure 4, RL = 3k, CL = 2500pF 0.22 1.9 3.1 µs

tPLH Driver Input to Output Figures 4, 10, RL = 3k, CL = 15pF 0.6 4 µs

tPHL Driver Input to Output Figures 4, 10, RL = 3k, CL = 15pF 0.6 4 µs

tPLH Receiver Input to Output Figures 5, 11 0.3 6 µs

tPHL Receiver Input to Output Figures 5, 11 0.4 6 µs

RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High)

tPLH Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF 15 40 70 ns

tPHL Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF 15 40 70 ns

tSKEW Driver Output to Output Figures 2, 7, RL = 54Ω, CL = 100pF 5 15 ns

tr, tf Driver Rise or Fall Time Figures 2, 7, RL = 54Ω, CL = 100pF 3 15 40 ns

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LTC1387

AC ELECTRICAL CHARACTERISTICSTA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.

The denotes specifications which apply over the full operatingtemperature range.Note 1: Absolute Maximum Ratings are those values beyond which the lifeof the device may be impaired.Note 2: All currents into device pins are positive; all currents out of devicepins are negative. All voltages are referenced to device ground unlessotherwise specified.

Note 3: All typicals are given at VCC = 5V, C1 = C2 = C3 = C4 = 0.1µFand TA = 25°C.Note 4: Short-circuit current for RS485 driver output low state folds backabove VCC. Peak current occurs around VO = 3V.Note 5: SLEW includes an internal pull-up in RS485 mode.

PIN FUNCTIONS

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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.VDD (Pin 3): Charge Pump Positive Supply Output.Requires an external 0.1µF capacitor to ground.A (Pin 4): Receiver Input A. Inverting input of RS232receiver A in RS232 mode; inverting RS485 receiver inputin RS485 mode.

B (Pin 5): Receiver Input B. Inverting input of RS232receiver B in RS232 mode; noninverting RS485 receiverinput in RS485 mode.Y (Pin 6): Driver Output Y. Inverting RS232 driver Y outputin RS232 mode; inverting RS485 driver output in RS485mode.Z (Pin 7): Driver Output Z. Inverting RS232 driver Z outputin RS232 mode; noninverting RS485 driver output inRS485 mode.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High)

tZL Driver Enable to Output Low Figures 3, 8, CL = 100pF, S1 Closed 50 90 ns

tZH Driver Enable to Output High Figures 3, 8, CL = 100pF, S2 Closed 50 90 ns

tLZ Driver Disable from Low Figures 3, 8, CL = 15pF, S1 Closed 50 90 ns

tHZ Driver Disable from High Figures 3, 8, CL = 15pF, S2 Closed 60 90 ns

RS485 Mode (Slow Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = Low)

tPLH Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF 100 700 1500 ns

tPHL Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF 100 700 1500 ns

tSKEW Driver Output to Output Figures 2, 7, RL = 54Ω, CL = 100pF 200 750 ns

tr, tf Driver Rise or Fall Time Figures 2, 7, RL = 54Ω, CL = 100pF 150 300 1500 ns

tZL Driver Enable to Output Low Figures 3, 8, CL = 100pF, S1 Closed 600 1500 ns

tZH Driver Enable to Output High Figures 3, 8, CL = 100pF, S2 Closed 600 1500 ns

tLZ Driver Disable from Low Figures 3, 8, CL = 15pF, S1 Closed 100 200 ns

tHZ Driver Disable from High Figures 3, 8, CL = 15pF, S2 Closed 100 200 ns

RS485 Mode (ON = RXEN = High, 485/232 = High)

tPLH Receiver Input to Output Figures 2, 9, RL = 54Ω, CL = 100pF 20 70 140 ns

tPHL Receiver Input to Output Figures 2, 9, RL = 54Ω, CL = 100pF 20 70 140 ns

tSKEW Differential Receiver Skew, tPLH – tPHL Figures 2, 9, RL = 54Ω, CL = 100pF 10 ns

Receiver Output Enable/Disable (ON = High)

tZL Receiver Enable to Output Low Figures 6, 12, CL = 15pF, S1 Closed 40 90 ns

tZH Receiver Enable to Output High Figures 6, 12, CL = 15pF, S2 Closed 40 90 ns

tLZ Receiver Disable from Low Figures 6, 12, CL = 15pF, S1 Closed 40 90 ns

tHZ Receiver Disable from High Figures 6, 12, CL = 15pF, S2 Closed 40 90 ns

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LTC1387

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485/232 (Pin 8): Interface Mode Select Input. A low logicinput enables two RS232 drivers and two RS232 receiv-ers. A high input enables the RS485 driver and the RS485receiver.DXEN (Pin 9): Driver Enable Input. A high logic inputenables the drivers and a low logic input disables thedrivers. When disabled, all driver outputs are in highimpedanceGND (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 inputenables the receivers and a low logic input disables thereceivers. When disabled, all receiver outputs are in highimpedance.ON (Pin 13): A high logic level at ON input keeps the chargepump active regardless of the state of the DXEN and RXENinputs. When the charge pump is active, the drivers andreceivers can be enabled or disabled without waiting forcharge pump stabilization time (typically 100µs with 0.1µFcapacitors). A low logic state at the ON, DXEN and RXENinputs 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 pumpshould be allowed to stabilize before data transmission.When DXEN and RXEN are high and ON is low, the chargepump, drivers and receivers are all active and the driveroutputs are internally looped back to the inputs of thereceiver. 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-wiremode – inputs ON and RXEN connected to one wire, DXENa separate wire; three-wire mode – separate wires to eachinput. See the Function Tables.DZ/SLEW (Pin 14): Driver Z or Slew Input. In RS232mode, this pin is the driver Z input. In RS485 mode, thispin controls the slew rate of the RS485 driver. With theSLEW pin high, the RS485 driver runs at maximum (fast)slew rate and can transmit signals up to 5MBd. With theSLEW pin low, the RS485 driver runs with reduced (slow)slew rate to control reflections with improperly terminatedcables. In slow mode, the RS485 driver can support datarates 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; thedifferential 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 19and 20.C2 + (Pin 20): Commutating Capacitor C2 PositiveTerminal.

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LTC1387

FU CTIO TABLESU U

Select ModesSELECT INPUTS RECEIVER DRIVER

ON RXEN DXEN 485/232 RXA RXB DXY DXZ

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 Z ON ON Z ON OFF RS232 Mode, DXY On,DXZ Off, RXA Off, RXB On

0 1 1 0 ON ON ON ON ON ON RS232 Loopback Mode, DXY and DXZ On,RXA and RXB On

0 0 0 X Z Z Z Z OFF OFF Shutdown, RS485 RIN

1 0 0 1 Z Z Z Z ON OFF RS485 Mode, DX and RX Off

X 0 1 1 Z Z ON ON ON OFF RS485 Mode, DX On, RX Off

X 1 0 1 ON Z Z Z ON OFF RS485 Mode, DX Off, RX On

1 1 1 1 ON Z ON ON ON OFF RS485 Mode, DX On, RX On

0 1 1 1 ON Z ON ON ON ON RS485 Loopback Mode, DX On, RX On

RS232 Driver ModeINPUTS OUTPUTS

SELECTED 485/232 D CONDITIONS Y, Z

YES 0 0 No Fault 1

YES 0 1 No Fault 0

YES 0 X Thermal Fault Z

NO 0 X X Z

RS232 Receiver ModeINPUTS OUTPUTS

SELECTED 485/232 A, B RA, RB

YES 0 0 1

YES 0 1 0

YES 0 Inputs Open 1

NO 0 X Z

RS485 Driver Slew RateINPUTS OUTPUTS

DXEN 485/232 SLEW SLEW RATE

1 1 0 Slow

1 1 1 Fast

0 1 X Z

RS485 Driver ModeINPUTS OUTPUTS

DXEN 485/232 D CONDITIONS Z Y

1 1 0 No Fault 0 1

1 1 1 No Fault 1 0

1 1 X Thermal Fault Z Z

0 1 X X Z Z

RS485 Receiver ModeINPUTS OUTPUTS

RXEN 485/232 B – A RA RB

1 1 < –0.2V 0 Z

1 1 > 0.2V 1 Z

1 1 Inputs Open 1 Zor Shorted to Ground

0 1 X Z Z

CHARGE PUMP LOOPBACK COMMENTS

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LTC1387

BLOCK DIAGRAM

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RS232 MODEWITHOUT LOOPBACK

ON13

RA

C2C1

RB

DY

DZ

B

A

VDD VCC

19

201

4

2

3

6

7

8

18

16

15

14Y

Z

5

17

GND

DXEN

485/232

10

9

LTC1387 • BD

RXEN12

11VEE

RS232 MODEWITH LOOPBACK

ON13

RA

C2C1

RB

DY

DZ

VDD VCC

19

201

2

3

6

7

8

18

16

15

14Y

Z

17

GND

DXEN*

485/232

10

9RXEN*

12

11VEE

RS485 MODEWITHOUT LOOPBACK

ON13

RA

C2C1

RB

DY

SLEW

B

A

VDD VCC

19

201

4

2

3

6

7

8

18

16

15

14

Y

Z

5

17

GND

DXEN

485/232*

10

9RXEN

12

11VEE

RS485 MODEWITH LOOPBACK

ON13

RA

C2C1

RB

DY

SLEW

VDD VCC

19

201

2

3

6

7

8

18

16

15

14

Y

Z

17

GND

DXEN*

485/232*

10

9RXEN*

12

11VEE

*485/232, DXEN, RXEN = VCC

TEST CIRCUITS

Figure 2. RS485 Driver/ReceiverTiming Test Circuit

Figure 1. RS485 DriverTest Load

R

R

VOD

Z

Y

LTC1387 • F01

VOC

RL

CL

LTC1387 • F02

Z

Y

CL B

RA

15pF

D

SLEW

485 = 3V, DXEN = 3V, RXEN = 3V

Figure 3. RS485 Driver OutputEnable/Disable Timing Test Load

DR OUT

CL

500Ω

S2

LTC1387 • F03

VCC

S1

Figure 4. RS232 DriverTiming Test Circuit

Figure 6. Receiver OutputEnable/Disable Timing Test Load

RECEIVEROUT

CL

1k

S2

LTC1387 • F06

VCC

S1

Figure 5. RS232 ReceiverTiming Test Circuit

LTC1387 • F05

15pF

Y, ZD RA, B

232 = 0V, DXEN = 3V, RXEN = 3V

RL

LTC1387 • F04

Y, ZD

CL

232 = 0V, DXEN = 3V

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LTC1387

SWITCHI G WAVEFOR SU W

Figure 9. RS485 Receiver Propagation Delays

3V

D

Y, Z

–VO

VOLTC1387 • F10

tPHL tPLH

0V

0V0V

1.5V 1.5V

Figure 10. RS232 Driver Propagation Delays

1.5V

3V

0V

D

f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE)f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE)

1.5V

Z – Y

–VO

VO

tSKEW

1/2 VO

LTC1387 • F07

tPLH

tr

90%50%

10%

tPHL

tf

90%50%

10%

VO

tSKEW

VDIFF = V(A) – V(B)

Z

Y

Figure 7. RS485 Driver Propagation Delays

1.5V

3V

0V

DXEN

f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE)f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE)

1.5V

Y, Z

VOL

5V

tZL tLZ

0.5VOUTPUT NORMALLY LOW

0VLTC1387 • F08

2.3V

2.3V

tZH

VOHOUTPUT NORMALLY HIGH

tHZ

0.5VZ, Y

Figure 8. RS485 Driver Enable and Disable Times

0V

VOD2

B – Af = 1MHz: tr ≤ 10ns: t f ≤ 10ns

1.5VR

VOL

VOH

LTC1387 • F09

tPLH tPHL

INPUT

–VOD2

OUTPUT

0V

1.5V

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LTC1387

SWITCHI G WAVEFOR SU W

VIH

A, B

R

VOL

VOHLTC1387 • F11

tPHL tPLH

VIL

2.4V

0.8V

1.3V 1.7V

Figure 11. RS232 Receiver Propagation Delays

1.5V

3V

0V

RXENf = 1MHz: tr ≤ 10ns: tf ≤ 10ns

1.5V

R

VOL

5V

tZL tLZ

0.5VOUTPUT NORMALLY LOW

0VLTC1387 • F12

1.5V

1.5V

tZH

VOHOUTPUT NORMALLY HIGH

tHZ

0.5VR

Figure 12. Receiver Enable and Disable Times

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I FOR ATIOBasic Theory of Operating

The LTC1387 is a single 5V supply, single-port logicreconfigurable RS485/RS232 transceiver with an onboardcharge pump. The interface port offers a flexible combina-tion of an RS485 driver and an RS485 receiver or twoRS232 drivers and two RS232 receivers. The RS485transceiver and the RS232 transceivers are designed toshare the same I/O pins. A logic input 485/232 controls theselection between RS485 and RS232 transceiver modes.The RS485 transceiver supports both RS485 and RS422standards, whereas the RS232 transceivers support bothRS232 and EIA562 standards. With four additional controlinputs: ON, DXEN, RXEN and SLEW, the LTC1387 caneasily be reconfigured via software to adapt to variouscommunication needs including a one-signal-line RS232I/O mode. Four examples of interface port connections areshown in Figures 13 through 16.

Both the interface drivers and the receivers feature three-state outputs. Driver outputs are forced into highimpedance when the driver is disabled, in the shutdownmode or with the power off. The driver outputs can beforced beyond power supply levels without damage up to±18V. The receiver inputs can withstand ±25V withoutdamage. The receiver input resistance is typically 24k inRS485 mode, shutdown mode or power off but drops to5k in RS232 mode.

In RS485 mode, the DXEN and RXEN control the three-state outputs of the driver and receiver respectively. TheSLEW input is active during RS485 mode and the logiclevel controls the differential driver slew rate. This pin hasan internal 5µA pull-up current source during the RS485mode. A high logic selects fast differential driver slew rateand a low logic selects slow slew rate. In slow slew mode,the maximum signal bandwidth is reduced, minimizing

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LTC1387

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PPLICATI

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I FOR ATIOEMI and signal reflection problems. Slow slew rate sys-tems can often use improperly terminated or evenunterminated cables with acceptable results. The RS485differential input receiver features an offset input thresh-old of –80mV at 0V common mode voltage. This allowsthe receiver output to have a known High output statewhen the inputs are open or shorted. The receiver alsofeatures an input hysteresis of 40mV. The charge pumpcan be kept active regardless of the state of DXEN andRXEN pins by keeping the ON pin High. This improves thereceiver response time by removing the 100µs chargepump start-up time.

In RS232 mode, the drivers and receivers can be selectedfrom the Function Tables with control inputs ON, RXENand DXEN. The receivers feature a typical 0.6V inputhysteresis.

All the interface driver outputs are fault protected by acurrent limiting and thermal shutdown circuit. The thermalshutdown circuit disables both the RS232 and RS485driver outputs when the die temperature reaches 150°C.The thermal shutdown circuit reenables the drivers whenthe die temperature cools to 135°C.

A loopback mode enables internal connections from driveroutputs to receiver inputs for self-test. The driver outputsare not isolated from the external loads during loopback.

The charge pump generates boosted positive voltage VDDand negative voltage VEE for true RS232 levels from asingle 5V VCC supply. The charge pump requires four0.1µF capacitors.

RA

RBDY

DZ

A

B

Y

Z

RA

RB

DY

DZ/SLEW

ONVCC

RXEN

DXEN

485/232

CONTROLLER

DX/RX

RXEN

DXENMODE

INTERFACE

A

B

RS232 RS485

RS485

RS232 RS232 RS485 RS485 SHUTDOWNTRANSMIT MODE RECEIVE MODE TRANSMIT MODE RECEIVE MODE MODE

RXEN = 0 RXEN = 1 RXEN = 0 RXEN = 1 RXEN = 0

DXEN = 1 DXEN = 0 DXEN = 1 DXEN = 0 DXEN = 0

MODE = 0 MODE = 0 MODE = 1 MODE = 1 MODE = X1387 • F13

LTC1387

Figure 13. Half-Duplex RS232 (1-Channel), Half-Duplex RS485

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LTC1387

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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.

Figure 14. Full-Duplex RS232 (1-Channel), Half-Duplex RS485

RA

RBDY

DZ

A

B

Y

Z

RA

RB

DY

DZ/SLEW

ONVCC

RXEN

DXEN

485/232

CONTROLLER

DX

RXEN

DXENMODE

INTERFACE

A

B

Y

Z

RS232 RS485

RS232 RS485

RS485

RS485

RS232 RS485 SHUTDOWNMODE MODE MODE

RXEN = 1 RXEN = 1 RXEN = 0

DXEN = 1 DXEN = 1 DXEN = 0

MODE = 0 MODE = 1 MODE = X1387 • F15

LTC1387

RX

RXD

TXD

Figure 15. Full-Duplex RS232 (1-Channel), Full-Duplex RS485/RS422

Figure 16. Full-Duplex RS232 (2-Channel), Full-Duplex RS485/RS422 with SLEW Control

RA

RBDY

DZ

A

B

Y

Z

RA

RB

DY

DZ/SLEW

ON

RXEN

DXEN

485/232

CONTROLLER

DX1

DX2/SLEW

ON

RXEN

DXENMODE

INTERFACE

A

B

Y

Z

RS232 RS485

RS232 RS485

RS485

RS485

RS232 RS485 SHUTDOWNMODE MODE MODE

ON = 1 ON = 1 ON = 0

RXEN = 1 RXEN = 1 RXEN = 0

DXEN = 1 DXEN = 1 DXEN = 0

MODE = 0 MODE = 1 MODE = X1387 • F16

LTC1387

RX1

RX2

RXD

RS232

CTS

TXD

RS232

RTS

RA

RBDY

DZ

A

B

Y

Z

RA

RB

DY

DZ/SLEW

ONVCC

RXEN

DXEN

485/232

CONTROLLER

DX

RXEN

DXENMODE

INTERFACE

A

B

RS232

RS232

RS485

RS485

RS232 RS485 RS485 SHUTDOWNMODE TRANSMIT MODE RECEIVE MODE MODE

RXEN = 1 RXEN = 0 RXEN = 1 RXEN = 0

DXEN = 0 DXEN = 1 DXEN = 0 DXEN = 0

MODE = 0 MODE = 1 MODE = 1 MODE = 01387 • F14

LTC1387

RX

TXD

RXD

12

LTC1387

sn1387 1387fs LT/GP 0197 7K • PRINTED IN USA

LINEAR TECHNOLOGY CORPORATION 1997

Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900FAX: (408) 434-0507 TELEX: 499-3977 www.linear-tech.com

Dimensions in inches (millimeters) unless otherwise noted.PACKAGE DESCRIPTION

U

SW Package20-Lead Plastic Small Outline (Wide 0.300)

(LTC DWG # 05-08-1620)

S20 (WIDE) 0396

NOTE 1

0.496 – 0.512*(12.598 – 13.005)

20 19 18 17 16 15 14 13

1 2 3 4 5 6 7 8

0.394 – 0.419(10.007 – 10.643)

9 10

1112

0.037 – 0.045(0.940 – 1.143)

0.004 – 0.012(0.102 – 0.305)

0.093 – 0.104(2.362 – 2.642)

0.050(1.270)

TYP 0.014 – 0.019(0.356 – 0.482)

TYP

0° – 8° TYP

NOTE 10.009 – 0.013

(0.229 – 0.330)0.016 – 0.050

(0.406 – 1.270)

0.291 – 0.299**(7.391 – 7.595)

× 45°0.010 – 0.029(0.254 – 0.737)

NOTE:1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDEDIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

***

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LTC1320 AppleTalk ® Transceiver AppleTalk /LocalTalk ® Compliant

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LTC1347 5V Low Power RS232 Transceiver Three Drivers/Five Receivers, Five Receivers Alive in ShutdownAppleTalk and LocalTalk are registered trademarks of Apple Computer Corp.

G Package20-Lead Plastic SSOP (5.3mm)(Reference LTC DWG # 05-08-1640)

G20 SSOP 0802

0.09 – 0.25(.0035 – .010)

0° – 8°

0.55 – 0.95(.022 – .037)

5.00 – 5.60**(.197 – .221)

7.40 – 8.20(.291 – .323)

1 2 3 4 5 6 7 8 9 10

6.90 – 7.50*(.272 – .295 )1718 14 13 12 11151619202.0

(.079)

0.05(.002)

0.65(.0256)

BSC0.22 – 0.38

(.009 – .015)

MILLIMETERS(INCHES)

DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDEDIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE

*

**

NOTE:1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE0.42 ±0.03 0.65 BSC

5.3 – 5.77.8 – 8.2

RECOMMENDED SOLDER PAD LAYOUT

1.25 ±0.12