TPS23881: how to configure driver to handle both 2-pair 30W and 4-pair 90W

Hi Stephane,

This is currently being looked into and an answer will be posted when available. Thanks!

Hi Darwin,
Concretely, how do you translate your explanation in register values?

For my PoE+ ports (Channel 1 & 2) with 30 watts maximum output power:

• 2-Pair Police Ch-1 Configuration Register (0x1E) and 2-Pair Police Ch-2 Configuration Register (0x1F) are set to 60 (30W)
• What about 4-Pair Police Ch-1 and 2 Configuration Register (0x2A)? Shall it remain set to 0xFF in order to run in 2-Pair mode only? Shall another value be set?

For my Hi-PoE port (Channel 3 & 4) with 90 watts maximum output power in 4-pair mode and 30 watts in 2-pair mode:

• I think 4-Pair Police Ch-3 and 4 Configuration Register (0x2B) shall be set to 180 (90W).
• What about the 2P registers? Shall 2-Pair Police Ch-3 Configuration Register (0x20) and 2-Pair Police Ch-4 Configuration Register (0x21) be set to 60 (30W)? Will it be ok to supply 2x45W in 4-pair mode?

Thank you for your help
Best Regards
Stephane

Hi Stephane,

NOTE: The policing registers are set automatically by the PSE in auto and semi-auto modes after power up based on the assigned class. The settings used are in the datasheet in Table 37, 38 and 47.

For my PoE+ ports (Channel 1 & 2) with 30 watts maximum output power:
You will set 0x29 power allocation to 2P, 30W.
2-Pair Police Ch-1 Configuration Register (0x1E) and 2-Pair Police Ch-2 Configuration Register (0x1F) are set to 60 (30W) for class 4 by the TPS23881 upon turn on in auto mode and semi-auto mode.
If you need a different value, you need to configure the 2P policing registers after power up.
4-Pair Police Ch-1 and 2 Configuration Register (0x2A) should remain at 0xFF. They do not apply to 2P channels.

For Channel 3 & 4 with 80 watts maximum output power:
You will set 0x29 power allocation to 4P, 90W.
2-Pair Police Ch-1 Configuration Register (0x1E) and 2-Pair Police Ch-2 Configuration Register (0x1F) are set to 60 (30W) for class 4 by the TPS23881 upon turn on in auto mode and semi-auto mode.
4-Pair Police Ch-1 and 2 Configuration Register (0x2A) are also set based on single signature or dual signature to total power needed by both channels. For class 8 single signature and class 5 dual signature this will be set to 90 watts.
If you need a different value, you need to configure the 2P and 4P policing registers after power up. It is OK to set 2X45W in 4P mode.

Regards,

Nitya

Hi Nitya,

My design mix PoE+ (Channel 1 & 2) and HiPoE (Channel 3 & 4) with the same TPS2881 so the power allocation register (0x29) has to be set to 90watts.

About the PoE+ port, your answer is clear : 2P policie registers are set to 30W, 4P policie register remains to 0xFF.

About the Hi-PoE port that can also handle PoE+, 2P policie registers are set to 30W while the 4P policie register is set to 90Watts. Is that right?

Thanks

Best Regards

Stephane

Hi Stephane,

For your configuration of

channel 1 for port 1 (30W PoE+)
channel 2 for port 2 (30W PoE+)
channels 3&4 for port 3 (90W HiPoE)
channels 5&6 for port 4 (90W HiPoE)
channel 7 for port 5 (30W PoE+)
channel 8 for port 6 (30W PoE+)

You should set 0x29 = 0xF3 for ports 1-4 and 0x29 = 0x3F for ports 5-8. This makes ports 1,2,7,8 2P ports, 3-4 and 5-6 as 4P ports. (how you set these bytes depends on whether you are using config A mode or config B mode). 

Regarding "About the Hi-PoE port that can also handle PoE+, 2P policie registers are set to 30W while the 4P policie register is set to 90Watts. Is that right?". I am not sure you want to set 2P pcut to 30W on both channels for the 90W case. 2P pcut  should be 45W so that port can support 90W on the 4 pairs.