7

LTC488/LTC489

S

APPLICATI

I FOR ATIO

Figure 5. Typical Connection

120

Ω

120

Ω

3

RX

2

1

488/9 F05

DX

1

3

SHIELD

RX

EN

DX

1/4 LTC486

12

SHIELD

4

12

3

2

DX

DX

1/4 LTC486

1

EN

1/4 LTC488 OR

1/4 LTC489

RX

3

1

2

4

RX

1/4 LTC488 OR

1/4 LTC489

EN

EN

FREQUENCY (MHz)

0.1

0.1

1

10

1

10

100

488/9 F06

Figure 7. Cable Length vs Data Rate

DATA RATE (bps)

10k

10

100

1k

10k

100k

1M

10M

488/9 F07

2.5M

Figure 6. Attenuation vs Frequency for Belden 9841

When using low loss cables, Figure 7 can be used as a

guideline for choosing the maximum line length for a given

data rate. With lower quality PVC cables, the dielectric loss

factor can be 1000 times worse. PVC twisted-pairs have

terrible losses at high data rates (> 100kbps), and greatly

reduce the maximum cable length. At low data rates

however, they are acceptable and much more economical.

Cable Termination

The proper termination of the cable is very important. If the

cable is not terminated with its characteristic impedance,

distorted waveforms will result. In severe cases, distorted

(false) data and nulls will occur. A quick look at the output

of the driver will tell how well the cable is terminated. It is