TPS23751 based POE, disabled from Adapter OR CPU

Salvo Mazzola

Other Parts Discussed in Thread: TPS23751

Hi,

I'm designing an IEEE802.3at type-2 powered device (PD) based on the TPS23751. It will operate with 'Option 3' (power applied to the output side of the converter) for diode ORing external power into the PD. The Adapter will have the priority. In my specific case I would like to disable the PSE source using the DEN pin when the Adapter is present or when a control signal coming from a CPU is asserted, see the schematic attached. Would this work?

Thanks.

TPS23751 POE.pdf

over 9 years ago

0 Darwin Fernandez over 9 years ago

TI__Mastermind 41760 points

Hi Salvo,

I see no issues with the schematic. It is what we recommend for these types of option 3 oring techniques.

0 Salvo Mazzola over 9 years ago in reply to Darwin Fernandez

Prodigy 140 points

Thank you Darwin. So connecting the output of the two optocoupler (one controlled by the CPU GPIO and one from the adapter) is going to work and disable the PSE right?

0 Darwin Fernandez over 9 years ago in reply to Salvo Mazzola

TI__Mastermind 41760 points

Hi Salvo,

This is a simple logic OR configuration of the optos. As long as it fully pulls down DET, it should be okay.

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TPS23751 based POE, disabled from Adapter OR CPU