THVD1429: Slew rate of A, B

Asaishi-san,

Slew rate could be derived based on the output differential amplitude (VOD) and rise/fall time (tr/tf) specifications. You could compute it as 0.8 * VOD / tr. The 0.8 factor is because the tr (or tf) specification is measured based on 10% and 90% amplitude thresholds.

Regards,

Max

Hi Max,

Thanks for the answer.

Could you show one example?
Because the test conditions between VOD and tr/tf are different and I couldn't imagine how should I calculate 0.8*VOD/tr.

I would appreciate if you show one example how to calculate.

Best regards,
Koyo

Koyo-san,

The typical tr/tf with a 54-Ohm load ("worst case" load for RS-485) is 300 ns.  The typical VOD for this condition is 3.5 V.  So, the slew rate would be 0.8 * (3.5 V) / (300 ns) = 9.3 V/us.

Regards,
Max

Hi Max,

Thanks for the clear comment.

One another question, does the driver input have limitation by slew rate?
I would like to know the driver input can detect correctly if input pulse signal is rounded and slow slew rate.

Best regards,
Koyo