TPS2372-3EVM-757: TPS2372-3EVM discussion

Hi Kygo,

Thanks for reaching out to us! Please find our comments below.

1. Your resistor configuration is Class-4, which may cause PSE turn off at 30 W.

2. TPS2372-3 supports Class-6 power rating but do not support Class-8 power. It has lower operation current limitation compared to TPS2372-4 (1.85 A to 2.2 A).

3. The number of class events is 6. Theoretically the events number should be always equal or less than 5. So it might be the PSE caused the LEDs looked strange.  

I am wondering if you want to run the TPS2372-3 at Class-4 power. If so, could you try to use a different type of PSE and see if the event number can be <= 5?

Best regards,

Diang 

I am wondering if you want to run the TPS2372-3 at Class-4 power.
-> Yes, I want to run the TPS2372-3 at Class-4 power.
If so, could you try to use a different type of PSE and see if the event number can be <= 5?
-> I try to use same PSE to run the TPS2372-3 at Class-3 power. The LED indicator shows Class 3/4. But the TPS2372-3 at Class-4 power, The LED indicator is not correct.

Hi Diang

So, I need to change the PSE, right? Do you have a recommended PSE? It needs to support Class 1 ~ Class 6.

Hi Jack,

Seems it is caused by the PSE. In the 802.3bt standard, the PSE events number won't be 6 at Class-4. (https://www.microsemi.com/document-portal/doc_view/136209-next-generation-poe-ieee-802-3bt-white-paper)

If you are looking for a off-the-shelf PSE, you can use Phihong's POE60U-1BT which is the Vendor #2 in my test if I remembered correctly.

If you are doing a PSE design, and you are considering TI's PSE product, you can choose TPS23881. There is also TPS23881EVM and assorted GUI for customer to do evaluation. Let me know if you are interested in that. 

Best regards,

Diang 

Hi Diang

In the TPS2372-3RGW datasheet, it is mentioned that the Class 5 MINIMUM POWER AT PD (W) is 25.5W, but here the PD Input Power (Min) is marked as 40W, which of these two is correct?

Hi Kygo,

The power limitation function is from the PSE (power sourcing equipment). The PD has pass FET current limiting function but it normally allows more power than the PSE's power limit at 37 - 57 V input voltage.

Here is how it works at Class-5:

1. In Class-5, PD is desired to request 0 - 40 W input power;

2. PSE can send up to 45 W output power to PD, and it may turn off the port if the demanded output power is higher than 45 W (programable). The difference between the PSE output power and PD input power are the power losses calculated at a 100-meter standard Ethernet cable.

3. If the cable is less than 100 meter, when PSE is working at the 45 W up limit, the input power of PD will be larger than 40 W.

Best regards,

Diang

Hi Diang

So, I can ignore MINIMUM POWER AT PD (W) value and focus on MAXIMUM POWER AT PD (W) value, right?

For example, if I have a 36W device. So, the PD can be set to class 5, not need to be set to class 6, right?

Hi Jack,

Yes, you need to consider the column of MAXIMUM POWER AT PD (12.95 W to 71 W).

The main purpose of classification is for power budgeting. If your device have 36 W, and your PD input to load efficiency is higher than 36/40 = 90%, you can choose Class 5. You can also choose Class 6 since both Class 5 and Class 6 use the same PSE type (Type 3). 

Updated on Jan/17/2023: It has been a relatively long period that we have not received your reply. I will close this thread for now. Please open a new thread if you have further questions.

Best regards,

Diang