LTC1689IS 데이터 시트보기 (PDF) - Linear Technology

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LTC1689IS

100Mbps RS485 Hot Swapable Quad Drivers

Linear Technology 

LTC1688/LTC1689

APPLICATIONS INFORMATION

High Speed Twisted-Pair Transmission

Data rates up to 100Mbps can be transmitted over short

distances using Category 5 UTP (unshielded twisted pair).

The cable distance will determine the maximum data rate.

Figures 11 and 12 show an 8ns pulse propagating over 25

feet of Category 5 UTP. Notice how the cable attenuates the

signal. Lucent Technologies’ BRF2A and BRS2A receivers

are recommended for these ultrahigh speed applications.

2V/DIV

2V/DIV

DRIVER INPUT

DRIVER OUTPUT

2V/DIV RECEIVER INPUT

High Speed Backplane Transmission

The LTC1688/LTC1689 can be used in backplane point-to-

point and multipoint applications. At high data rates,

signals should be routed differentially and PC traces

should be terminated (see Figure 13). Note that the RS485

specification calls for characteristic impedances near 100Ω;

therefore, PC trace transmission lines should be designed

with an impedance close to 100Ω. If trace impedance is

much less than 100Ω, and the trace is double terminated,

the part will experience excess heating. The propagation

delay could then fall outside the specified window. The

LT1720 dual UltraFastTM comparator is a good choice for

high data rate backplane applications.

UltraFast is a trademark of Linear Technology Corporation.

5V/DIV RECEIVER OUTPUT

10ns/DIV

1688/89 F11

Figure 11. 8ns Pulse Over 25 Feet Category 5 UTP

DRIVER

100Ω

100Ω

25 FT CATEGORY 5 UTP

+

RECEIVER

–

1/4 LTC1688

1688/89 F12

Figure 12. 100Mbps Differential Data Connection

1/4 LTC1688

DRIVER

BACKPLANE

TRANSMISSION LINE 100Ω

1/2 LT1720

RECEIVER

Figure 13. 100Mbps Backplane Transmission

1688/89 F13

16889fa

9

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