Datasheet LTC1387 Datasheet (Linear Technology)

L TC1387

Single 5V RS232/RS485

Multiprotocol Transceiver

EATU

F

■

Two RS232 Transceivers or One RS485 Transceiver

■

Operates from a Single 5V Supply

■

Guaranteed Receiver Output with Inputs

RE

S

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

U

APPLICATIONS

■

Point-of-Sale Terminals

■

Software Selectable Multiprotocol Interface Ports

■

Low Power RS485/RS422/RS232/EIA562 Interface

■

Cable Repeaters

■

Level Translators

DUESCRIPTIO

The LTC®1387 is a low power reconfigurable CMOS bidi­rectional 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 require­ments 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 re­ceiver 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.

A

PPLICATITYPICAL

V

CC1

5V

RECOUT

DR IN
SLEW

DR ENABLE

U

O

12

3

LTC1387

18

17

15
14

9

12

5V

11

1920

4
5

6
7

8
13

10

120Ω

5V
5V

ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE

RS485 INTERFACE

4000-FT 24-GAUGE TWISTED PAIR

120Ω

LTC1387

4
5

6
7

8

5V

13

5V

10

212019

3
18

17

15
14

9
12

11

V

CC2

5V

RECOUT

DR IN
SLEW

DR ENABLE
5V

LTC1387 • TA01

1

LTC1387

WU

U

PACKAGE

/

O

RDER I FOR ATIO

A

W

O

LUTEXI T

S

A

WUW

ARB

U
G

I

S

(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 ............................... –0.3V to (VCC + 0.3V)

Short-Circuit Duration

Output........................................................ Indefinite

VDD, VEE, 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

TOP VIEW

+

1

C1



–

2

C1



3

V

DD

4

A

5

B

6

Y

7

Z

8

485/232

9

DXEN

10

GND

G PACKAGE

20-LEAD PLASTIC SSOP

T

= 125°C, θJA = 120°C/W (G)

JMAX

= 125°C, θJA = 75°C/W (SW)

T

JMAX

Consult factory for Military grade parts.

20
19
18
17
16
15
14
13
12
11



SW PACKAGE

20-LEAD PLASTIC SO



C2+

–

C2



V

CC

R

A

R

B

D

Y

DZ/SLEW
ON
RXEN
V

EE

ORDER PART

NUMBER

LTC1387CG
LTC1387CSW
LTC1387IG
LTC1387ISW

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

V

OD1

V

OD2

∆V

OD

V

OC

∆VOC Change in Magnitude of Driver Common Mode Figure 1, R = 27Ω or R = 50Ω ● 0.2 V

I

OSD

I

OZD

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

V

O

I

OSD

Driver Inputs and Control Inputs

V

IH

V

IL

I

IN

Differential Driver Output Voltage (Unloaded) IO = 0 ● 6V
Differential Driver Output Voltage (With Load) Figure 1, R = 50Ω (RS422) ● 2.0 6 V

Figure 1, R = 27Ω (RS485) ● 1.5 6 V

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

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

Output Voltage for Complementary Output States
Driver Short-Circuit Current VO = –7V, 12V; VO = High ● 35 250 mA

VO = –7V, 12V; VO = Low (Note 4) ● 10 250 mA

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

Output Voltage Swing Figure 4, RL = 3k, Positive ● 5 6.5 V

Figure 4, RL = 3k, Negative ● –5 –6.5 V

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

Input High Voltage DY, DZ, DXEN, RXEN, ON, 485/232, SLEW ● 2V
Input Low Voltage DY, DZ, DXEN, RXEN, ON, 485/232, SLEW ● 0.8 V
Input Current DY, DZ, DXEN, RXEN, ON, 485/232 ● ±0.1 ±10 µA

SLEW (Note 5)

● 5 15 µA

2

L TC1387

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)

V

TH

∆V

TH

I

IN

R

IN

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

V

TH

∆V

TH

R

IN

Receiver Output (ON = RXEN = High)

V

OH

V

OL

I

OSR

I

OZR

Power Supply Generator

V

DD

V

EE

Power Supply

I

CC

Differential Input Threshold Voltage –7V ≤ VCM ≤ 12V ● –0.20 0.20 V
Input Hysteresis VCM = 0V 40 mV
Input Current (A, B) VIN = 12V ● 1mA

= –7V ● –0.8 mA

V

IN

Input Resistance –7V ≤ VIN ≤ 12V ● 12 24 kΩ

Receiver Input Voltage Threshold Input Low Threshold ● 0.8 V

Input High Threshold

● 2.4 V

Receiver Input Hysteresis 0.6 V
Receiver Input Resistance VIN = ±10V 3 5 7 kΩ

Receiver Output High Voltage IO = –3mA, VIN = 0V, 485/232 = Low ● 3.5 4.6 V
Receiver Output Low Voltage IO = 3mA, VIN = 3V, 485/232 = Low ● 0.2 0.4 V
Short-Circuit Current 0V ≤ VO ≤ V

CC

● 785mA

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

VDD Output Voltage No Load, ON = DXEN = RXEN = High 8 V

= –5mA, ON = DXEN = RXEN = High 7 V

I

DD

VEE Output Voltage No Load, ON = DXEN = RXEN = High –7.7 V

= 5mA, ON = DXEN = RXEN = High –7.0 V

I

EE

VCC Supply Current No Load, ON = DXEN = RXEN = High ● 725mA

Shutdown, ON = DXEN = RXEN = 0V

● 5 100 µA

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

SR Slew Rate Figure 4, RL = 3k, CL = 15pF ● 30 V/µ s

Figure 4, R

t

T

t

PLH

t

PHL

t

PLH

t

PHL

Transition Time Figure 4, RL = 3k, CL = 2500pF ● 0.22 1.9 3.1 µs
Driver Input to Output Figures 4, 10, RL = 3k, CL = 15pF ● 0.6 4 µs
Driver Input to Output Figures 4, 10, RL = 3k, CL = 15pF ● 0.6 4 µs
Receiver Input to Output Figures 5, 11 ● 0.3 6 µs
Receiver Input to Output Figures 5, 11 ● 0.4 6 µs

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

t

PLH

t

PHL

t

SKEW

t

, t

r

f

Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 15 40 70 ns
Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 15 40 70 ns
Driver Output to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 515 ns
Driver Rise or Fall Time Figures 2, 7, RL = 54Ω, CL = 100pF ● 31540 ns

= 3k, CL = 1000pF ● 4V/µs

L

3

LTC1387

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

t

ZL

t

ZH

t

LZ

t

HZ

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

t

PLH

t

PHL

t

SKEW

tr, t

f

t

ZL

t

ZH

t

LZ

t

HZ

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

t

PLH

t

PHL

t

SKEW

Receiver Output Enable/Disable (ON = High)

t

ZL

t

ZH

t

LZ

t

HZ

The ● 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.

Driver Enable to Output Low Figures 3, 8, CL = 100pF, S1 Closed ● 50 90 ns
Driver Enable to Output High Figures 3, 8, CL = 100pF, S2 Closed ● 50 90 ns
Driver Disable from Low Figures 3, 8, CL = 15pF, S1 Closed ● 50 90 ns
Driver Disable from High Figures 3, 8, CL = 15pF, S2 Closed ● 60 90 ns

Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 100 700 1500 ns
Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 100 700 1500 ns
Driver Output to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 200 750 ns
Driver Rise or Fall Time Figures 2, 7, RL = 54Ω, CL = 100pF ● 150 300 1500 ns
Driver Enable to Output Low Figures 3, 8, CL = 100pF, S1 Closed ● 600 1500 ns
Driver Enable to Output High Figures 3, 8, CL = 100pF, S2 Closed ● 600 1500 ns
Driver Disable from Low Figures 3, 8, CL = 15pF, S1 Closed ● 100 200 ns
Driver Disable from High Figures 3, 8, CL = 15pF, S2 Closed ● 100 200 ns

Receiver Input to Output Figures 2, 9, RL = 54Ω, CL = 100pF ● 20 70 140 ns
Receiver Input to Output Figures 2, 9, RL = 54Ω, CL = 100pF ● 20 70 140 ns
Differential Receiver Skew, t

Receiver Enable to Output Low Figures 6, 12, CL = 15pF, S1 Closed ● 40 90 ns
Receiver Enable to Output High Figures 6, 12, CL = 15pF, S2 Closed ● 40 90 ns
Receiver Disable from Low Figures 6, 12, CL = 15pF, S1 Closed ● 40 90 ns
Receiver Disable from High Figures 6, 12, CL = 15pF, S2 Closed ● 40 90 ns

PLH

– t

 Figures 2, 9, R

PHL

= 54Ω, CL = 100pF 10 ns

L

Note 3: All typicals are given at V
and TA = 25°C.

Note 4: Short-circuit current for RS485 driver output low state folds back
above V

Note 5: SLEW includes an internal pull-up in RS485 mode.

. Peak current occurs around VO = 3V.

CC

= 5V, C1 = C2 = C3 = C4 = 0.1µF

CC

UUU

PIN FUNCTION S

C1+ (Pin 1): Commutating Capacitor C1 Positive Terminal.
Requires an external 0.1µ F 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 RS232

receiver A in RS232 mode; inverting RS485 receiver input
in RS485 mode.

4

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.

L TC1387

U

UU

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.
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 100µ s with 0.1µF
capacitors). A low logic state at the ON, DXEN and RXEN
inputs will put the transceiver and charge pump in shut­down mode and reduces ICC to 5µ A. Whenever the trans­ceiver 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: one­wire 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 5µ A pull­up 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 0.1µ F capacitor between Pins 19
and 20.

C2+ (Pin 20): Commutating Capacitor C2 Positive
Terminal.

5

LTC1387

UU

FU CTIO TABLES

Select Modes

SELECT 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,

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,

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

0 0 0 X Z Z Z Z OFF OFF Shutdown, RS485 R
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

CHARGE PUMP LOOPBACK COMMENTS

RXA and RXB On

DXZ Off, RXA Off, RXB On

RXA and RXB On

IN

RS232 Driver Mode

INPUTS

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

OUTPUTS

RS232 Receiver Mode

INPUTS

SELECTED 485/232 A, B R

YES 0 0 1
YES 0 1 0
YES 0 Inputs Open 1

NO 0 X Z

OUTPUTS

RS485 Driver Slew Rate

INPUTS

DXEN 485/232 SLEW SLEW RATE

1 1 0 Slow
1 1 1 Fast
01X Z

OUTPUTS

RS485 Driver Mode

INPUTS OUTPUTS

DXEN 485/232 D CONDITIONS Z Y

, R

A

B

1 1 0 No Fault 0 1
1 1 1 No Fault 1 0
1 1 X Thermal Fault Z Z
01XXZZ

RS485 Receiver Mode

INPUTS OUTPUTS

RXEN 485/232 B – A R

1 1 < –0.2V 0 Z
1 1 > 0.2V 1 Z
1 1 Inputs Open 1 Z

or Shorted to Ground

01 X ZZ

R

A

B

6

BLOCK DIAGRAM

L TC1387

W

RS232 MODE

WITHOUT LOOPBACK

2

V

DD

485/232

3
4

A

5

B

6

Y

7

Z

8

9

DXEN

10

GND

*485/232, DXEN, RXEN = V

TEST CIRCUITS

Y

R

V

OD

V

OC

R

RS485 MODE

DXEN

GND

SLEW

2
3

4

A

5

B

6

Y

7

Z

8

9

10

D

WITHOUT LOOPBACK

Y

R

Z

201

C2C1

19
18

17
16

15

14
13

12
11

L

V

CC

R

A

R

B

D

Y

SLEW
ON
RXEN

V

EE

V

DD

485/232

DXEN*

GND

C

L

C

L

201

C2C1

19
18

17

16
15
14

13
12

11

CC

V

CC

R

A

R

B

D

Y

D

Z

ON
RXEN

V

EE

V

DD

485/232*

WITH LOOPBACK

2
3

6

Y

7

Z

8

9

10

A

B

RS232 MODE

R

15pF

RS485 MODE

DD

Y

Z

GND

DR OUT

WITH LOOPBACK

2
3

6
7

8

9

10

500Ω

C

L

V

CC

201
19

18

V

17

R

16

R

15

D

14

SLEW

13
12

11

LTC1387 • BD

S1

S2

CC

A

B
Y

ON

RXEN*
V

EE

C2C1

201

C2C1

19
18

V

17

R

16

R

15

D

14

D

13

12
11

CC

A

B

Y

Z

ON

RXEN*
V

EE

V

485/232*

DXEN*

Z

LTC1387 • F01

Figure 1. RS485 Driver
Test Load

Y, Z

D

C

L

232 = 0V, DXEN = 3V

Figure 4. RS232 Driver
Timing Test Circuit

R

L

LTC1387 • F04

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

Figure 2. RS485 Driver/Receiver
Timing Test Circuit

Y, Z

D

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

A, B

R

Figure 5. RS232 Receiver
Timing Test Circuit

LTC1387 • F02

15pF

LTC1387 • F05

LTC1387 • F03

Figure 3. RS485 Driver Output
Enable/Disable Timing Test Load

V

CC

S1

C

1k

L

S2

LTC1387 • F06

RECEIVER

OUT

Figure 6. Receiver Output
Enable/Disable Timing Test Load

7

LTC1387

U

W

SWITCHI G WAVEFOR S

f = 1MHz: t
f = 100kHz: t

3V

1.5V

t

PLH

50%

10%

O

Figure 7. RS485 Driver Propagation Delays

f = 1MHz: t
f = 100kHz: t

1.5V

t

ZL

t

ZH

Figure 8. RS485 Driver Enable and Disable Times

Z – Y

DXEN

Y, Z

Z, Y

D

0V

V

O

–V

O

Y

V

Z

3V

0V

5V

V

OL

V

OH

0V

≤ 10ns: tf ≤ 10ns (FAST SLEW RATE MODE)

r

≤ 10ns: tf ≤ 10ns (SLOW SLEW RATE MODE)

r

90%

t

r

t

SKEW

≤ 10ns: tf ≤ 10ns (FAST SLEW RATE MODE)

r

≤ 10ns: tf ≤ 10ns (SLOW SLEW RATE MODE)

r

2.3V

2.3V

V

= V(A) – V(B)

DIFF

1/2 V

O

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

1.5V

1.5V

t

PHL

90%

t

LZ

t

HZ

50%

10%

t

f

t

LTC1387 • F07

SKEW

0.5V

0.5V

LTC1387 • F08

8

B – A

–V

R

Y, Z

V

V

OD2

OD2

V

f = 1MHz: t

0V

t

PLH

OH

OL

≤ 10ns: tf ≤ 10ns

r

1.5V

INPUT

OUTPUT

0V

t

PHL

1.5V

LTC1387 • F09

Figure 9. RS485 Receiver Propagation Delays

3V

D

0V

V

O

–V

O

1.5V

t

PHL

0V

1.5V

t

PLH

0V

LTC1387 • F10

Figure 10. RS232 Driver Propagation Delays

L TC1387

U

W

SWITCHI G WAVEFOR S

V

IH

A, B

R

RXEN

V

IL

V

OH

V

OL

3V

0V

5V

R

V

OL

V

OH

R

0V

1.3V

Figure 11. RS232 Receiver Propagation Delays

1.5V

Figure 12. Receiver Enable and Disable Times

t

t

t

PHL

ZL

ZH

0.8V

f = 1MHz: t

1.5V

1.5V

≤ 10ns: tf ≤ 10ns

r

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

1.7V

1.5V

t

t

HZ

t

PLH

2.4V

LZ

0.5V

0.5V

LTC1387 • F11

LTC1387 • F12

PPLICATI

A

U

O

S

I FOR ATIO

WU

U

Basic Theory of Operating

The LTC1387 is a single 5V supply, single-port logic
reconfigurable RS485/RS232 transceiver with an onboard
charge pump. The interface port offers a flexible combina­tion of an RS485 driver and an RS485 receiver or two
RS232 drivers and two RS232 receivers. The RS485
transceiver and the RS232 transceivers are designed to
share the same I/O pins. A logic input 485/232 controls the
selection between RS485 and RS232 transceiver modes.
The RS485 transceiver supports both RS485 and RS422
standards, whereas the RS232 transceivers support both
RS232 and EIA562 standards. With four additional control
inputs: ON, DXEN, RXEN and SLEW, the LTC1387 can
easily be reconfigured via software to adapt to various
communication needs including a one-signal-line RS232
I/O mode. Four examples of interface port connections are
shown in Figures 13 through 16.

Both the interface drivers and the receivers feature three­state outputs. Driver outputs are forced into high
impedance when the driver is disabled, in the shutdown
mode or with the power off. The driver outputs can be
forced beyond power supply levels without damage up to
±18V. The receiver inputs can withstand ±25V without
damage. The receiver input resistance is typically 24k in
RS485 mode, shutdown mode or power off but drops to
5k in RS232 mode.

In RS485 mode, the DXEN and RXEN control the three­state outputs of the driver and receiver respectively. The
SLEW input is active during RS485 mode and the logic
level controls the differential driver slew rate. This pin has
an internal 5µA pull-up current source during the RS485
mode. A high logic selects fast differential driver slew rate
and a low logic selects slow slew rate. In slow slew mode,
the maximum signal bandwidth is reduced, minimizing

9

LTC1387

PPLICATI

A

U

O

S

I FOR ATIO

WU

U

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. The charge pump
can be kept active regardless of the state of DXEN and
RXEN pins by keeping the ON pin High. This improves the
receiver response time by removing the 100µs charge
pump start-up time.

In RS232 mode, the drivers and receivers can be selected
from the Function Tables with control inputs ON, RXEN
and DXEN. The receivers feature a typical 0.6V input
hysteresis.

All the interface driver outputs are fault protected by a
current limiting and thermal shutdown circuit. The thermal
shutdown circuit disables both the RS232 and RS485
driver outputs when the die temperature reaches 150°C.
The thermal shutdown circuit reenables the drivers when
the die temperature cools to 135°C.

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

The charge pump generates boosted positive voltage V

DD

and negative voltage VEE for true RS232 levels from a
single 5V VCC supply. The charge pump requires four

0.1µF capacitors.

RS232 RS485

A

INTERFACE

B

 RS232 RS232 RS485 RS485 SHUTDOWN

TRANSMIT 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 = X

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

RS485

LTC1387

R

A

B

D

Y

Z

D

A

R

A

R

B

R

B

Y

D

Y

DZ/SLEW

Z

ON
RXEN
DXEN
485/232

V

CC

DX/RX

CONTROLLER
RXEN

DXEN
MODE

1387 • F13

10

L TC1387

R

A

R

B

D

Y

D

Z

A

B

Y

Z

R

A

R

B

D

Y

DZ/SLEW
ON

V

CC

RXEN
DXEN
485/232

CONTROLLER
DX

RXEN
DXEN

MODE

INTERFACE

A

B

RS232

RS232

RS485

RS485

 RS232 RS485 RS485 SHUTDOWN

 MODE 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 = 0

1387 • F14

LTC1387

RX

TXD

RXD

PPLICATI

A

INTERFACE

O

RS232

A

RXD

B

RS232 RS485

Y

TXD

Z

U
S

I FOR ATIO

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

RS485

RS485

RS485

LTC1387

A

B

D

Y

Y

Z

D

Z

WU

R

R

A

B

U

R

A

R

B

D

Y

DZ/SLEW
ON

RXEN
DXEN
485/232

V

CC

RX

CONTROLLER
DX

RXEN
DXEN

MODE

 RS232 RS485 SHUTDOWN

 MODE MODE MODE

 RXEN = 1 RXEN = 1 RXEN = 0
 DXEN = 1 DXEN = 1 DXEN = 0
 MODE = 0 MODE = 1 MODE = X

1387 • F15

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

RS232

A

B

INTERFACE

Y

Z

RS485

RXD

RS232

RS485

CTS

RS232 RS485

TXD

RS232

RS485

RTS

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

LTC1387

R

Y

Z

A

R

A

R

B

R

B

D

Y

DZ/SLEW
ON

RXEN
DXEN
485/232

RX1
RX2

CONTROLLER

DX1
DX2/SLEW

ON
RXEN

DXEN
MODE

 RS232 RS485 SHUTDOWN

 MODE 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 = X

A

B

D

Y

Z

D

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 represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

1387 • F16

11

LTC1387

PACKAGE DESCRIPTION

0.205 – 0.212**
(5.20 – 5.38)

U

Dimensions in inches (millimeters) unless otherwise noted.

G Package

20-Lead Plastic SSOP (0.209)

(LTC DWG # 05-08-1640)

0.278 – 0.289*
(7.07 – 7.33)



1718 14 13 12 1115161920

0.068 – 0.078
(1.73 – 1.99)

0° – 8°

0.005 – 0.009
(0.13 – 0.22)

*

DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH 


SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD 
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



0.022 – 0.037
(0.55 – 0.95)

0.0256
(0.65)

BSC

0.010 – 0.015
(0.25 – 0.38)

0.002 – 0.008
(0.05 – 0.21)

SW Package

20-Lead Plastic Small Outline (Wide 0.300)

(LTC DWG # 05-08-1620)

0.291 – 0.299**
(7.391 – 7.595)

0.010 – 0.029

(0.254 – 0.737)

0.009 – 0.013

(0.229 – 0.330)

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 SIDE

*

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

**




NOTE 1

× 45°

0.016 – 0.050

(0.406 – 1.270)

0.093 – 0.104

(2.362 – 2.642)

0° – 8° TYP

0.050

(1.270)

TYP

0.014 – 0.019

(0.356 – 0.482)

TYP

0.037 – 0.045

(0.940 – 1.143)

NOTE 1

0.004 – 0.012

(0.102 – 0.305)

12345678910

0.496 – 0.512*

(12.598 – 13.005)

19 181716

20

2345678

1

14 13

15

0.301 – 0.311
(7.65 – 7.90)

G20 SSOP 0595

1112

910

0.394 – 0.419

(10.007 – 10.643)

S20 (WIDE) 0396

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

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LTC1320 AppleTalk® Transceiver AppleTalk/LocalTalk® Compliant
LTC1321/LTC1322/LTC1335 RS232/EIA562/RS485 Transceivers Configurable
LTC1323 Single 5V AppleTalk Transceiver AppleTalk /LocalTalk Compliant 10kV ESD
LTC1334 Single Supply RS232/RS485 Transceiver Single 5V Supply, Configurable
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AppleTalk and LocalTalk are registered trademarks of Apple Computer Corp.

1387f LT/GP 0197 7K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1997

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-741 7 ● [phone]
FAX: [phone]

●

TELEX: 499-3977 ● www.linear-tech.com