Datasheet SN75LBC786DW Datasheet (Texas Instruments)

HHLHLLHHHHH

SN75LBC786

QUADRUPLE RS-423-B DRIVER/RECEIVER WITH LOOPBACK

SLLS184 – NOVEMBER 1994

D

Four Independent Drivers and Receivers

D

Loopback Mode Functionally Self Tests
Drivers and Receivers Without
Disconnection From Line

D

Driver Slew Rate Controlled by a Single
Resistor

D

Internal Thermal-Overload Protection

D

RS-423-B Inputs and Outputs Designed to
Withstand ±25 V

D

ESD Protection Exceeds 2000 V Per
MIL-STD-833C Method 3015

D

LinBiCMOS Process Technology

description

The SN75LBC786 is a monolithic quadruple

DW PACKAGE

3A
3Z

3LB

4A
4Z

4LB

V

SS

GND

4B
4Y
3B
3Y
3C
4C

(TOP VIEW)

1

28

2

27

3

26

4

25

5

24

6

23

7

22

8

21

9

20

10

19

11

18

12

17

13

16

14

15

2LB
2Z
2A
1LB
1Z
1A
R

WS

V

DD

1Y
1B
2Y
2B
2C
1C

RS-423-B driver and receiver with integrated­loopback function. The operation of the
SN75LBC786 is closely based on that of the SN75186. In normal operation, the device performs as four
independent RS-423-B driver/receiver pairs designed to interface data-terminal equipment (DTE) with data
circuit-terminating equipment (DCE). In loopback mode, the signal from each driver output is fed back via
special circuitry into its associated receiver input, removing the need to locally disconnect cables and install a
loopback connector. The receiver output signal is the same as the driver input signal.

The SN75LBC786 is characterized for operation over the temperature range of 0°C to 70°C.

FUNCTION TABLE

LOOPBACK

LB

H L HL L H
H H HL L L

H
H
H
H

L
L

H = high level, L = low level, X = irrelevant, ? = indeterminate

INPUTS OUTPUTS

A B C Z Y

L

L

L

H

L

H

L

H

L
H
H

X
X

L
H
H

X
X

?
?
?
?

L

H

L

H

L

H

L
L

L

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

LinBiCMOS is a trademark of Texas Instruments Incorporated.

PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Copyright  1994, T exas Instruments Incorporated

1

SN75LBC786
QUADRUPLE RS-423-B DRIVER/RECEIVER WITH LOOPBACK

SLLS184 – NOVEMBER 1994

logic diagram (positive logic) (each transceiver)

Driver

A

LB

Y

Z

Receiver

–
+

C
B

absolute maximum ratings over operating free-air temperature range (unless otherwise noted)

Positive supply voltage, V
Negative supply voltage, V

Receiver input voltage range –30 V to 30 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Driver input voltage range –0.5 V to 5.75 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Loopback input voltage range –0.5 V to 5.75 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Driver output voltage range (supplies at 0 V) –30 V to 30 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Driver output voltage range (supplies at ±12 V) –25 V to 25 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Continuous power dissipation at (or below) T
Operating free-air temperature range, T
Storage temperature range, T

Case temperature for 10 seconds 260°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

†

Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

NOTE 1: All voltages are with respect to network ground terminal.

(see Note 1) 14 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DD

–14 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS

= 70°C 800 mW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A

0°C to 70°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

–65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

stg

A

recommended operating conditions

MIN NOM MAX UNIT

Supply voltage, V
Supply voltage, V
High-level input voltage, V
Low-level input voltage, V
High-level output current, I
Low-level output current, I
Slew rate control resistor, R
Operating free-air temperature, T

DD
SS

IH

IL

OH

OL

WS

Driver and loopback 2 V
Driver and loopback 0.8 V
Receiver –4 mA
Receiver 4 mA

A

10.8 12 13.2 V

–10.8 –12 –13.2 V

20 82 820 kΩ

0 70 °C

†

2

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IDDSupply current (loopback off)

mA

ISSSupply current (loopback off)

mA

s

(see Figure 1)

L

s

(see Figure 1)

SN75LBC786

QUADRUPLE RS-423-B DRIVER/RECEIVER WITH LOOPBACK

SLLS184 – NOVEMBER 1994

DRIVER SECTION

electrical characteristics over recommended ranges of supply voltage and operating free-air
temperature (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

V

OH

V

OL

I

IH

I

IL

I

IKG

I

OS(H)

I

OS(L)

I

DD(LB)

I

DD

LOOPBACK MODE

High-level output voltage Open circuit or RI = 450 Ω 4 5.5 6 V
Low-level output voltage Open circuit or RI = 450 Ω –6 –5.5 –4 V
High-level input current VI = 2.4 V – 5.5 V 100 µA
Low-level input current VI = 0 V – 0.8 V –100 µA
Output leakage current VDD = VSS = 0 V, VO = ±6 V –100 100 µA
High-level short-circuit output current VI = high, VO = 0 V 15 45 mA
Low-level short-circuit output current VI = low, VO = 0 V –45 –15 mA

pp

Supply current with loopback on No load, LB at 0.8 V 13 16 mA

pp

Supply current with loopback on No load, LB at 0.8 V –13 –16 mA

Output voltage (input either high or low) RI = >450 Ω, VLB = low –6 –5.5 –4 V

p

p

No load, LB at 2 V 10 12
RI = 450 Ω, LB at 2 V 60 70

No load, LB at 2 V –10 –12
RI = 450 Ω, LB at 2 V –60 –70

switching characteristics over recommended ranges of supply voltage and operating free-air
temperature (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

RWS = 0 kΩ 1.5

Transition time, low-to-high level output

t

TLH

RI = 450 Ω, CL = 50 pF,
VWS = 5 V

Transition time, high-to-low level output

t

THL

SR Output slew rate RWS = 20 kΩ 15 V/µs
t

sk

Output skew, |t

PHL

– t

| (see Figure 4) RWS = 82 kΩ 1 µs

PLH

RWS = 20 kΩ 1.5 2.1 2.7
RWS = 82 kΩ 5 8 11
RWS = 820 kΩ 80
RWS = 0 kΩ
RWS = 20 kΩ 1.5 2.1 2.7
RWS = 82 kΩ 5 8 11
RWS = 820 kΩ 80

1.5

µ

µ

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3

SN75LBC786

V

g

mV

IIInput current

Other input to GND

mA

VOHHigh-level output voltage (see Note 2)

V

0.15

1µs

C

pF

20

200

ns

QUADRUPLE RS-423-B DRIVER/RECEIVER WITH LOOPBACK

SLLS184 – NOVEMBER 1994

RECEIVER SECTION

electrical characteristics over recommended ranges of supply voltage and operating free-air
temperature (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

IT

V

hys

V

OL

I

OS

V

ID

V

ofs

NOTES: 2. Device has an internal RX supply regulator . Maximum RX logic output voltage under no load is thus defined by an internal voltage

Receiver input threshold voltage
(see Figure 5)

p

Hysteresis voltage 20 40 150 mV

p

Low-level output voltage IO = 20 µA to 4 mA 0.4 V
RX short circuit current 50 mA
Differential input voltage Receiver inputs open circuit 1.6 2.1 2.6 V
Fail safe output voltage See Note 3 3.5 V

value. This is nominally set to 4.5 V with a tolerance of ±5%.

3. One input at ground, other input open circuit, IO = –20 µA, or both open circuit.

VIT = (VI+ – VI–) –200 200
VIT = (VI+ – VI–) with 500-Ω series resistor
VI = 10 V
VI = –10 V

IO = –20 µA 3.5 5
IO = –4 mA 2.4 5

p

–400 400

1.3 3.25

–3.25 –1.3

switching characteristics over recommended ranges of supply voltage and operating free-air
temperature (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN NOM MAX UNIT

t

PLH

t

PHL

t

THL

t

TLH

Propagation delay time, low-to-high (see Figure 2)
Propagation delay time, high-to-low (see Figure 2)
Transition time, high-to-low (see Figure 3)
Transition time, low-to-high (see Figure 3)

= 50

L

p

4

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QUADRUPLE RS-423-B DRIVER/RECEIVER WITH LOOPBACK

PARAMETER MEASUREMENT INFORMATION

5 V

R

Input

51 Ω

GND

NOTES: A. CL includes probe and jig capacitance.

B. The input pulse is supplied by a generator having the following characteristics: tr ≤ 10 nS, tf < 10 nS, Zo = 50 Ω, PRR ≥ 5 kHz, duty

cycle = 50%, V

WS

max

V

DD

V

SS

= 3 V, V

R

L

GND

= 0 V.

min

Figure 1. Driver Transition T imes

Output
C

L

(see Notes A and B)

Input

Output

SN75LBC786

SLLS184 – NOVEMBER 1994

3 V

0 V

V

OH

V

OL

t

THL

90% 90%

10% 10%

t

TLH

V

DD

Input

GND

NOTES: A. CL includes probe and jig capacitance.

B. The input pulse is supplied by a generator having the following characteristics: tr ≤ 10 nS, tf < 10 nS, Zo = 50 Ω, PRR ≥ 5 kHz, duty

cycle = 50%, V

51 Ω

+

–

max

V

SS

GND

= 0.5 V, V

Output

C

= –0.5 V.

min

L

Figure 2. Receiver Propagation Delay Times

V

DD

Input

GND

NOTES: A. CL includes probe and jig capacitance.

B. The input pulse is supplied by a generator having the following characteristics: tr ≤ 10 nS, tf < 10 nS, Zo = 50 Ω, PRR ≥ 5 kHz, duty

cycle = 50%, V

51 Ω

max

+

–

V

SS

= 0.5 V, V

GND

min

Output

C

L

= –0.5 V.

(see Notes A and B)

Output

Input

(see Notes A and B)

Output

Input

V

OH

V

OL

t

PLH

t

TLH

50%

50%

90%

10% 10%

50%

90%

50%

t

PHL

t

THL

0.5 V

–0.5 V

Figure 3. Receiver Transition Times

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5

SN75LBC786
QUADRUPLE RS-423-B DRIVER/RECEIVER WITH LOOPBACK

SLLS184 – NOVEMBER 1994

PARAMETER MEASUREMENT INFORMATION

500 Ω

500 Ω

V

cm

Input A

Output Y

50% 50%

t

PLH

50% 50%

t

PHL

250 mV

250 mV

Vcm = –7 to 7 V

Figure 4. Skew Definition Times Figure 5. Input Balance Test

PRINCIPLES OF OPERATION

In normal operation, the SN75LBC786 functions as four independent drivers and receivers. The loopback mode is
disabled by maintaining a high logic level on the LB
hysteresis and resistive attenuation on the inputs. The resistive attenuation improves the input common-mode range
and also provides additional protection from ESD and over-voltage stress. The differential and common-mode input
impedance are sufficiently high to meet RS-423-B. The balance of the receiver input voltage current characteristics
and bias voltage is such that the receiver remains in the intended binary state when a differential voltage of 500 mV
is applied to the inputs through 500 Ω across the entire common-mode range (see Figure 5).

The drivers meet all RS-423-B specifications. In normal operation, the drivers have built-in current limits and thermal
overload protection. Slew-rate controlling circuitry is included into the design that is adjusted to suit the application
by means of an external resistor. The slew-rate controlling circuitry also has a default mode. If R
V externally, the transition time defaults to approximately 1.5 µs. The receiver is compatible to the RS-232 with the
use of external input resistors to meet the RS-232 input-resistance specification of 3 kΩ to 7 kΩ.

input. The receivers consist of differential comparators with

is shorted to 5

WS

T aking an individual LB

input low activates the loopback mode in the corresponding driver/receiver pair. This causes
the output from that driver to be fed back to the input of its receiver through dedicated internal-loopback circuitry . Data
from the receiver output can then be compared, by a communication system, with the data transmitted to the driver
to determine if the functional operation of the driver and receiver together is correct.

In the loopback mode, external data at the input of the receiver is ignored and the driver does not transmit data onto
the line. Extraneous data is prevented internally from being sent by the driver in the loopback mode by clamping its
output to a level below the maximum interface voltage, –5 V , or the EIA-423-B marking state. Below this marking level,
a reduced 1.5-V output amplitude is used at the driver output. This signal is detected by an on-chip loopback
comparator and fed to the input stage of the receiver to complete the loop.

Line faults external to the SN75LBC786 are detected in addition to device failures. These line faults include short
circuits to ground and to external supply voltages. The loopback mode should be entered only when the driver output
is low, that is, the marking condition. It is recommended that loopback not be entered when the driver output is in a
high state as this may cause a low-level, nondamaging oscillation at the driver output.

6

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