PM8805 PoE Classification issues

LukeIma · ‎2026-02-19

Hi everyone,

I'm working on a prototype, which is using a PM8805 to classify connected PoE types.

However we are running into an issue, where neither T0, T1 or T2 are giving us any signals (giving always 1 on their open drain signals, making .the LEDs stay off).

Suspecting an issue with our prototype, we went on to get a STEVAL-POE001V1, which is showing the same scenario: With our different PoE, PoE+ and PoE++ injectors (Both Ubiquity and TP-Link brand), the T0, T1 and T2 LEDs are remaining off. The PGD LED is however on in those tests. We tested with and without a load on the output (for example 5kOhm) to prevent the injectors going into standby mode.

We checked and according to datasheets the TP-Link TL-POE160S is an active 802.3af/at compliant injector.

Is my understanding correct? With the CLS 1 resistor at 36.5Ohm and the CLS2 resistor at 51.1Ohm, the T0, T1 and T2 signals should, as an example, be 0, 1, 1 respectively for a Type 2 PSE-PD (PoE+ according to IEEE 802.3) as shown in Table 10 of the PM8805 Datasheet.

Any help would be greatly appreciated.

Peter BENSCH · ‎2026-03-05

Welcome @LukeIma, to the community!

Your understanding of the T0/T1/T2 encoding with CLS1 = 36.5Ω and CLS2 = 51.1Ω resistors is correct: for a Type 2 (PoE+) PSE the PM8805 should report 'T2:T1:T0 = 1:1:0', as shown in line 2 of table 10 of the data sheet.

The fact that PGD is asserted but all T0...T2 lines stay high (LEDs off on STEVAL-POE001V1 and your own board) suggests that the PM8805 does not detect the PSE as an IEEE‑802.3af/at/… compliant source, but rather as a legacy / passive injector or in a non‑standard mode.

To investigate further, could you please share:

the exact test setup (cabling, injector mode/settings, power level),
scope screenshots of VPORT and the CLS1/CLS2 pins during startup,
confirmation that the injectors are set to 802.3af/at mode (not “passive PoE” or vendor‑specific mode)

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

View solution in original post

Peter BENSCH · ‎2026-03-05

Welcome @LukeIma, to the community!

Your understanding of the T0/T1/T2 encoding with CLS1 = 36.5Ω and CLS2 = 51.1Ω resistors is correct: for a Type 2 (PoE+) PSE the PM8805 should report 'T2:T1:T0 = 1:1:0', as shown in line 2 of table 10 of the data sheet.

The fact that PGD is asserted but all T0...T2 lines stay high (LEDs off on STEVAL-POE001V1 and your own board) suggests that the PM8805 does not detect the PSE as an IEEE‑802.3af/at/… compliant source, but rather as a legacy / passive injector or in a non‑standard mode.

To investigate further, could you please share:

the exact test setup (cabling, injector mode/settings, power level),
scope screenshots of VPORT and the CLS1/CLS2 pins during startup,
confirmation that the injectors are set to 802.3af/at mode (not “passive PoE” or vendor‑specific mode)

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Peter BENSCH · ‎2026-03-26

@LukeIma Is the question answered with that, or can you still provide the information?

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

LukeIma · ‎2026-04-09

@Peter BENSCH Thank you for your reply!
After much investigation we found that both the Ubiquity and TP-Link brand injectors where in fact not always compliant.
After switching to a certified industrial injector it now works.

Thank you so much for your reply
Regards

LukeIma · ‎2026-04-09

Yes my question was answered
Thank you very much