AM26C31: How to know line driver's max. signaling rate

Vincent Chen64988

Part Number: AM26C31

Hi Team,

My customer is surveying RS422 line driver - AM26C31/2, but he cannot find the max. signaling rate shown in datasheet (RS485 transceiver parts have this kind of information). So, how can he know this parameter in line driver/receiver datasheet? Or, what kind of parameters in datasheet can be used to calculate out the max. signaling rate?

Thanks very much.

Vincent Chen

over 7 years ago

0 Dierk Bronner over 7 years ago

TI__Intellectual 1645 points

Hi Vincent,

thank you for reaching out. The data rate of this device is determined by tr(OD), tf(OD)Differential output rise and fall times. Shown at chapter 6.8 Switching Characteristics at page 7 of the datasheet.

the max data rate can be calculated as followed:

A rule of thumb is take the max rise / fall time of the driver and divide by 0.3. You then invert this to get the data rate. For example for the AM26C31 RS422 transceiver has a maximum rise and fall time of 12 ns. The calculation would be 1/(12 ns/0.3 s). This result corresponds to 25 Mbps.

Since The RS422 has the same limitations on data rate vs cable length as the RS485 standard the maximum speed is 10 Mbps. So the AM26C31 provides enough headroom. For more information, pleas take a look here:

https://e2e.ti.com/support/interface/industrial_interface/w/industrial_interface/2512.rs485-communication-speed-vs-bus-length

Let me know if this is hlping you out, don't hesitate to ask further questions

Kind regards

Dierk