PoE PD TPS23756 detection issue.

Nicky Lim

Genius 3195 points

Other Parts Discussed in Thread: TPS23756, TPS23756EVM

Hello,

One of customer make PoE PD board using TPS23756 as attached schematic.

But it cannot be detected some PSE device or detected only as Class 3 even if change the Classification resistor.

Or there is no PD power.

So, customer wants to get schematic review.

Could you review attached schematic and let me get the result ASAP?

Regards,

Nicky

POE_PD_TPS23756.pdf

over 7 years ago

0 JCHK over 7 years ago

TI__Mastermind 43630 points

HI Nicky,

The divider used on the PPM pin (R74 & R75) may be effecting the detection. Have you tried removing R74 to see if detection and classification can work properly?

Regards,

0 Nicky Lim over 7 years ago in reply to JCHK

Genius 3195 points

Hi John,

After removing R74, End-Span doesn't work.
Before remove it, End-Span & Mid-Span works but detected only as Class 3.

Please review schematic again, and let me get your review result.

Regards,
Nicky

0 Darwin Fernandez over 7 years ago in reply to Nicky Lim

TI__Mastermind 40120 points

Hi Nicky,

Do you have schematic of PD front end like RJ45 to PoE PD that we can look at? Have you tried testing the PSE with the EVM to see if it's the PSE? What part number is PSE?

0 Nicky Lim over 7 years ago in reply to Darwin Fernandez

Genius 3195 points

Hi Darwin,

Attached RJ45 to PD schematic.

Customer is using Microsemi PD69200 + PD69208 PSE Solution and test complete with other PD solution and Spliter.

But does not test with TPS23756EVM because she doesn't have it.

Regards,

Nicky

PD_RJ45.pdf

0 Nicky Lim over 7 years ago in reply to Darwin Fernandez

Genius 3195 points

Hi Darwin,

Is there any updates?
Please let me get your answer ASAP.

Regards,
Nicky

0 Darwin Fernandez over 7 years ago in reply to Nicky Lim

TI__Mastermind 40120 points

Hi Nicky,

I did not see any issue on the schematics. Looking at only PSE's product page (unable to view datasheet), this looks like a controller+PSE combo. Perhaps you have to set the PSE to do type 2 hardware classification? You may want to try testing the TPS23861EVM to know for sure. This is a PSE that can startup to automatic mode and do type 2 hardware classification automatically.

Regards,

Darwin

0 Nicky Lim over 7 years ago in reply to Darwin Fernandez

Genius 3195 points

Hi Darwin,

At first, you recommended PPD pin pull down instead of Vdd divider by removing R74, but problem was not cleared.
Do you still recommend PPD pin pull down?
Customer wants to know which one is better, pull down or voltage divide?

Please let me get your answer ASAP.

Regards,
Nicky

0 Darwin Fernandez over 7 years ago in reply to Nicky Lim

TI__Mastermind 40120 points

Hi Nicky,

If you don't expect to use PPD functionality described in the datasheet, this should be pulled down to VSS or left floating.

0 Nicky Lim over 7 years ago in reply to Darwin Fernandez

Genius 3195 points

Hi Darwin,

You mean if want to use PPD function, attached schematic also fine. Am I right?

Regards,
Nicky

0 Darwin Fernandez over 7 years ago in reply to Nicky Lim

TI__Mastermind 40120 points

Hi Nicky,

PPD function is typically used for example in front end adapter applications like in Figure 34 in the datasheet. It looks different than your schematic where it's at the PoE input. Is this your intention? Looking at the divider you chose, the load will turn on at 14V. This would be a non-standard solution and might not inter-operate with compliant PSEs because this within the detection and class ranges. As John also commented, the resistor divider at 10V (detection) is pulling ~200uA. This can corrupt the detection of a compliant PSE.

0 bogdan cojocariu over 7 years ago in reply to Nicky Lim

Prodigy 60 points

Hi Darwin,

Please kindly advise where can I send my schematic for the PoE+ switch to be checked in order to make sure the detection works fine.
Currently I have done a design that works but did not get all PoE+ switches to work with it. The HP PoE+ switch does not work with my design.
Please kindly advise.
Kind Regards, Bogdan

0 Darwin Fernandez over 7 years ago in reply to bogdan cojocariu

TI__Mastermind 40120 points

Hi Bogdan,

What is the HP model number? Can you attach the schematic for us to review?

0 bogdan cojocariu over 7 years ago in reply to Darwin Fernandez

Prodigy 60 points

Hi Darwin,

Please kindly find below the HP model number:
HP Model HP 1910-8G-PoE+ switch.

Please note I cannot make public the schematic.
Please advise a contact detail from TI to which I can send the schematic.
I signed NDA papers and do not want to have any legal problems.
I look forward to receiving your advice.

Kind Regards, Bogdan

0 Darwin Fernandez over 7 years ago in reply to bogdan cojocariu

TI__Mastermind 40120 points

Hi Bogdan,

The datasheet says it has multiple allocations for PoE: automatic, 802.3af, LLDP. It looks like you might have to set the switch up to do hardware classification. Typically there is software that comes with the switch where you can configure these things.

Also, can you take a waveform of VDD-VSS when the switch is connected to see the PSE/PD interaction? Also, can you describe what the PD is doing when it connects to the switch? Is it turning on first before shutting down? Thanks!

0 bogdan cojocariu over 7 years ago in reply to Darwin Fernandez

Prodigy 60 points

Hi Darwin,

Please note the board that is not turning on is not turning on at all with the HP PoE+ switch but is turning on with a different PoE+ switch.

Kind Regards, Bogdan

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PoE PD TPS23756 detection issue.