Due to the multipoint nature of the bus, contention between

drivers may occur. This will not cause damage to the drivers

since they feature short-circuit protection and also thermal

shutdown protection. Thermal shutdown senses die tem-

perature and puts the driver outputs into TRI-STATE if a fault

condition occurs that causes excessive power dissipation

which can elevate the junction temperature to +150˚C.

A typical multipoint application is shown in the following fig-

ure. Note that termination is typically required but is only lo-

cated at the two ends of the cable (not on every node). Com-

monly pull up and pull down resistors may be required at one

end of the bus to provide a failsafe bias. These resistors pro-

vide a bias to the line when all drivers are in TRI-STATE. See

National Application Note 847 for a complete discussion of

failsafe biasing of differention buses.

DS012920-16

www.national.com

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