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THVD1500: bitrate changing in datasheet

Slava Prokopii
Intellectual 2065 points
Part Number: THVD1500

Hello,

after we've selected THVD1500 for our project, the datasheet for this device was changed. Max bitrate was changed from 300 to 500 kbps.

Was these datasheet changes made because of new hardware inside the chip, or it just was updated after additional performance tests?

Now we need a transceiver with 400 kbps bitrate. Can we be sure, that we can use THVD1500 or there is a probability of getting devices with 300kpbs limitation?

Thank you.

  • 0
    TI__Guru 62910 points

    Hello Slava,

    The hardware was not changed.  The datasheet was changed because while the device was originally designed with 300 kbps in mind, after release we had several customers inquire about operation up to 500 kbps and we realized it was achievable with the design as-is.

    To be honest although bit rate is a ubiquitous spec in transceiver datasheets it is really more of a system-level spec rather than than something that would be a direct property of an analog transceiver (which performs no data sampling and has no internal clock).  By system-level, I mean it would depend partly on transceiver characteristics like output rise/fall times but also on the cabling characteristics (i.e., how much jitter is introduced by the high-frequency losses associated with parasitic inductance and capacitance) and the host UART's ability to properly sample the serial data stream (which is influenced by its sampling point configuration and the frequency and accuracy of its internal bit clock).

    To simplify things, we generally say that a transceiver can support a given bit rate as long as the differential output rise/fall time makes up no more than 25-30% of the bit period.  This allows each bit to reach a steady-state value and have enough "settling" time to be reliably sampled in most systems.  At 500 kbps each bit would be 2000 ns long.  The maximum rise/fall time of the THVD1500 driver is 450 ns, so it should not present a limitation in 500 kbps applications.  Please let me know if this is not clear or if you have further questions.

    Max