Slew Rate Programming

The slew rate for the ADM5170 is controlled by a single resistor

connected between the SRA pin and GND. The slew rate is

approximately.

Slew Rate (V/

µs) = 20/R

Resistors between 2 k

Ω and 10 kΩ may be used providing a slew

rate which may be varied from 10 V/

µs to 2.2 V/µs. Figure 5 in the

Typical Performance Characteristics section shows how the slew

rate varies with R

(10% to 90%) varies with R

Waveshaping of the output allows

the user to control the level of interference (near-end crosstalk)

which may be coupled to adjacent circuits in an interconnection.

The recommended output characteristics for cable length and data

rate are given in the EIA RS-423A specifications.

Maximum Data Rate (kB/s) = 300/t (for rates from 1 kB/s to

100 kB/s).

Cable Length (feet) = 100 X t (Max Length = 4000 ft.)

where t is the transition time (in

µs) for the output to swing from

10% to 90% of its steady state values. The absolute maximum data

rate is 100 kB/s and the maximum cable length is limited to 4000 ft.

Output Mode Programming

The ADM5170 has two programmable output modes which

provide different output voltage levels. The low output mode meets

the specifications of EIA standards RS-423A while the high output

mode meets the RS-232 specifications. The high output mode

provides greater output swings and is suitable for driving lines

where higher attenuation levels must be tolerated. This mode is

selected by connecting the mode select pins to the supplies, MS+ to

V

ing both mode select pins MS+ and MS– to GND. This mode

provides a controlled output swing with lower output levels.

Inputs

Outputs

MS+

MS–

EN

Data

Output

GND

GND

0

0

5 V to 6 V (RS-423)

GND

GND

0

1

–5 V to –6 V (RS-423)

V

DD

V

SS

00

(V

1

V

DD

V

SS

01

(V

1

X

X

1

X

High Z

Typical Application Circuit

A typical application circuit using a single driver in the ADM5170

is shown in Figure 4. This circuit is suitable for either RS-232 or

RS-423 communication. An ADM5180 octal receiver is used to

translate the signal back to CMOS logic level at the receiving end.

1/8

ADM5170

EN

TIE TO GND

FOR RS-232

INPUT

RS-232/RS-422A

TRANSMISSION

+V

–V

1/8

ADM5180

PIN FUNCTION DESCRIPTION

Mnemonic

Function

V

DD

Power Supply Input, +10 V

± 10%.

V

SS

Power Supply Input, –10 V

± 10%.

GND

Ground Pin. Must be connected to 0 V.

A

Digital Input to Drivers A to H.

A

RS-232/RS-423 Output from Drivers A to H.

EN

Enable Pin. When high, all outputs are 3-stated.

MS+, MS–

Mode Select Inputs. Used to control the output

level swing. With MS+ & MS– connected to GND,

RS-423A output levels are selected. With MS+

connected to V

RS-232 output levels are developed.

SRA

Slew Rate Adjust Input. An external resistor (2 k

Ω

to 10 k

Ω) connected between this pin and GND is

used to control the Output Slew Rate (10 V/

µs to

2.2 V/

µs).

REV.

–4–

ADM5170

PIN CONFIGURATION

PLCC

NC = NO CONNECT

MS+

EN

26

27

28

4

2

3

15

18

17

16

12

14

13

25

24

21

20

19

23

22

TOP VIEW

(Not to Scale)

1

5

6

9

10

11

7

8

ADM5170

Figure 4. RS-232/RS-423A Typical Application Circuit

A