LT1785/LT1785A/

LT1791/LT1791A

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APPLICATIONS INFORMATION

Slew Limiting for EMI Emissions Control

The LT1785/LT1791 feature controlled driver output slew

rates to control high frequency EMI emissions from equip-

ment and data cables. The slew limiting limits data rate

operation to 250kbaud. Slew limiting also mitigates the

adverse affects of imperfect transmission line termina-

tion caused by stubs or mismatched cable. In some low

speed, short distance networks, cable termination may

be eliminated completely with no adverse effect on data

transmission.

Data Network Cable Selection and Termination

Long distance data networks operating at high data trans-

mission rates should use high quality, low attenuation

cable with well-matched cable terminations. Short distance

networks at low data rates may use much less expensive

PVC cable. These cables have characteristic impedances

as low as 72Ω. The LT1785/LT1791 output drivers are

guaranteed to drive cables as low as 72Ω.

Figure 9. Full-Duplex RS422

5

4

3

2

A

B

Z

Y

12

11

10

9

RO

RE

DE

DI

178591 F09

TX

120Ω

5

4

3

2

A

B

Z

Y

12

11

10

9

RO

LT1791

LT1791

RE

DE

DI

RX

TX

120Ω

RX