Hey all,
I currently have a system where I need to distribute one signal to multiple receivers over a bus on the backplane (multi-drop bus configuration). Because the bus exists over a backplane, the stub length to each receiver is going to end up being somewhat long (greater than 1 inch). According to this document, http://www.ti.com/lit/an/slla108a/slla108a.pdf (section 3.1.3), the max stub length is determined by the driver's transition time (stub length propagation time needs to be less than 30% of a driver's transition time). In the case of an M-LVDS driver, the transition time is at least 1ns, meaning stubs can have a maximum propagation delay of 300 ps. Assuming a propagation delay of 170ps per inch, then this would allow me a maximum stub length of ~1.7 in.
1) Can anyone tell me what is the transition time for the SN65LVDM179 driver (note that this is LVDM, not M-LVDS)?
2) Does the same general rule (propagation delay of stub <= 30% of transition time) for determining stub length for an M-LVDS driver still apply to LVDM drivers?
3) Where do I even find the transition time parameter in these datasheets? From my understanding, it is the time it takes from when the driver input voltage reaches Vih and when the driver output voltage reaches 90% of Vod. It sounds sort of like a propagation delay, but not quite.
Thanks for your time, everyone.
James M.
