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TPS23861 POE doubts on isolation

Shreenidhi Patil
Expert 3926 points
Other Parts Discussed in Thread: TPS23861, TIDA-00290, LM5019

Hello Team

My customer VVDN is making an Access point

He is using POE PSE controller from TI tps23861

 

I have a few queries on the same

 

 

We are using the quad port PSE Controller "TPS23861" as suggested by you. We find a reference design "TIDA-00290" based on the same on TI website. We have some doubts regarding that design. 

 

It has two modes of operation:

 

1. "Auto Mode" in which all the micro processor/controller pins "SCL, SDAI, SDAO, SHTDWN, RESET, INT & A3 are not used.

2. "Semi Auto Mode" in which it can be controlled by the host processor using I2C & other interface signals.

 

I want to know the functionality of "SHTDWN" pin in detail. Can we left it unconnected in "Semi Auto Mode",or we need to tie it to VDD or is it necessary to interface this pin with the host processor. What will be the consequences in each case. Please describe in detail. 

 

Similarly please help me understand  the same for Pin "A3"

I understand it will be used in case of multiple PSE controller ,

But in my case I have used only 1 port and only 1PSE controller in the entire system ,

So I believe even the SHTDWN pin need not be handled

 

 

Also in the TIDA-00290

In the mother board schematic

please help me understand why the buffer is used rather than just a Simple short

 

what relation does this SDA and SDAO have with isolation

 

I mean if we are making an isolated system is it necessary to have a 3wire i2C communication between uC and PSE

 

What is PSE_SDAO for ?

 

  • 0
    TI__Genius 15685 points

    Hi Shreenidhi,

    Please see my comments below:

    1. SHTDWN pin is used to fast shut down ports. To enable this function, you will need to configure register 0x15 to make the SHTDWN pin have impact on ports. If the the AUTO bit is register 0x11 is set, the SHTDWN pin has impact on each port by default. If you don't want to use this pin, you can tie it to VDD
    2. A3 pin's status has impact on bit 3 in the I2C slave address register. If you only have one device in the system and don't want to program TPS23861's address you can tie it to GND or VDD.
    3. SDAO and SDAI can be simply shorted if you use an isolator  which has bidirectional channel(ex:ISO1541D). Since the isolator(ISO7241) on EVM only has unidirectional channel, we need a buffer to add SDAO to the SDA line and block signal coming from MCU to go to SDAO line.

    In addition, please refer to TPS23861EVM-612 which has the latest design (updated the DCDC with UVLO: LM5019). If you want to learn more about PoE, please visit the PoE FAQ page. Thanks.

    Best regards,

    Penny