SP504AN

SP504 Application Note

© Copyright 2000 Sipex Corporation

5

The tri-state enable and disable timing must be

considered. Given two systems, each config-

ured in DTE/DCE operation, containing two

SP504’s each, System 1 is the DTE, and

System 2 is the DCE. Assume System 1 is now

configured to a DCE and System 2 is config-

ured to a DTE; the two SP504 devices within

each system will have to switch states. If

System 1 switches to DCE before System 2

tri-states its driver, the bus will share driver

outputs until System 2 switches to DTE, thus

causing bus contention problems. In both

systems, the active SP504 should be tri-stated

first before enabling the tri-stated SP504. Al-

though the bus contention will not damage the

SP504 devices, it should be avoided to prevent

short circuit currents at the driver outputs.

One last consideration for DTE/DCE hookup is

the charge pump capacitors. Many have in-

quired about sharing the 22

µF caps. For a mini-

mal requirement, the C1 and C2 capacitors must

be separate for each SP504 device. Although

this can be functionally done, Sipex does not

recommend this practice. Please be aware that

if one SP504 becomes nonfunctional, it can

affect the other SP504 as well.