TPS23861EVM-612: Connecting TPS2378EVM to TPS23861EVM-612

Hi Howard,

I have notified our PSE expert.

- Tom

Hi Howard,

Because the TPS2378EVM you use is a single signature PD which only has one PD controller. When it is connected to a 2-pair port, one PSE channel will implement detect and class and as a result it shows normal operation.

But when you connect it to a 4-pair port, there are two PSE channels in it and these two channels will implement detect at the same time, which means there are two current source flowing through the detection resistor and generate a higher voltage. As a result, the resistor it detects will be doubled and this is invalid.

Every time you run the PI-Commander, the GUI will scan/read the address of the device. For the default values are 20 and 28, unless you want to change the address, the GUI will just read the register and won't write the address in to the EEPROM.

Thank you.
Best Regards
Jack Chen

Hi Jack,

For our system, we will be using a 4-pair port with 2 PSE channels.

Does this mean that any PD configured as per the TPS2378 will not correctly detect for the reasons you have stated?

What purpose does the circuit configuration of the TPS2378 serve? Is it to allow Mode A or Mode B wiring to be used on a single PSE channel?

Howard

Hi Howard,

In your system, you need a dual signature PD which have two PD controller for each PSE channel.

If you use software to control 4-pair ports, you can use a single signature PD which only has one PD controller. But you can't implement detect and class for two channels at the same time.

TPS2378 has two kinds of EVM. One is a single PD TPS2378EVM-105, the other is a dual PD TPS2378EVM-602.

It is recommended that you use TPS2378EVM-602 which is a dual PD. This will work with 4-pair port of TPS23861EVM.

And our TPS23861 can only support ALT A, so you can just use Mode A wiring.

Thank you.

Best Regards

Jack Chen

Hi Jack,

Just for my understanding -

The TPS2378EVM-105 will only identify correctly to a PSE using a single controller. The 63R4 resistor identifies it as  CLASS4 giving a power range of 12.95W to 25.5W achievable down one channel (2x pairs).

As the eval board also makes use of the other channel (two pairs) i presume these can only be used if the PSE is configured to sense the CLASS on one pair and then supply power to channels? So, non standard?

Sorry, i just want to understand the way this board is meant to work even though its no use on our system!

Howard