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Original question:

TPS23881: 802.3bt compliance tests

TPS23882: 802.3at PoE+ compliance

Hanno Reimer
Intellectual 1680 points
Part Number: TPS23882

We are currently designing an industrial PoE switch with 8 ports and built-in 120W DC/DC converter.
The TPS23882 chip is used, which should provide max. 30W per port. (802.3at)
I have a question about a parameter that is measured by our Sifos PoE tester. Our tester only supports 802.3at with 30W per channel.
But the chipset is described as 802.3bt. In the protocols of Sifos the so-called Class Time is measured with approx. 97ms (802.3bt allowed 88-105ms).
https://www.ti.com/lit/ug/slvt185/slvt185.pdf?ts=1606742928780 
With 802.3at PoE+, however, the parameter is only permitted between 5.6 and 30ms. For the 23882 the parameter is fixed in the data sheet.
We are now somewhat confused, because we do not know whether we can call our switch 802.3bt compatible.
Other parameters like autoclass and low MPS are, as far as I know, only from 802.3bt 4PPoE in the standard.

  • 0
    TI__Mastermind 40720 points

    Hi Hanno,

    Just to give some background, the BT standard added some features like long first class finger and BT (Type 3) can still apply to the lower power levels like 30W (.at power levels) and is backwards compatible/interoperable with .at PDs. In a way, BT absorbed AT. So yes, older .at SIFOS equipment will fail the class timing spec because BT PSEs can output the first long class finger per the BT standard. However it will still be interoperable with AT compliant PDs in the industry.

    We've been recommending our customers to switch to the new BT SIFOS equipment. Thanks!