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Original question:

TPS23881EVM-008: Hardware design problem

TPS23881EVM-008: TPS23881 schmatic design suggestions

Lin GarHao
Prodigy 50 points
Part Number: TPS23881EVM-008
Other Parts Discussed in Thread: TPS23881, ISO6741, ISO7241C

Hi team,

The attachment is designed based on the reference circuit (TPS23881EVM-008) provided by our company. If it needs to be modified, please provide suggestions.

Due to time constraints, we hope to complete the modification before 1/17, thank you.

TPS23881 schematic design.pdf

  • 0
    TI__Genius 14645 points

    Hi Lin,

    This is very short turn around, typically schematic reviews should leave 1-week lead time. However, I have compiled some comments below: 

    1. Remove Pin 52 AUTO connection. TPS23881 does not support autonomous mode and therefore, this pin has no functionality. 

    2. ISO7241 is not recommended for new designs. I would consider changing to different 4 channel bidirectional digital isolater. Recommend using ISO6741.

    3. The pullups are 10K which are probably fine but I am bigger fan of stronger pullups. I recommend using 3.3K. INT pin can stay 10K. 

    Regards,

    Brandon

  • 0 in reply to Brandon Beader
    Prodigy 50 points

    Hi, thanks for your reply, regarding response 1 and 2, I have some questions below：

    1. It means that the Auto pin can be left open?

    2. (1) Reasons why ISO7241 is not recommended?

        (2) Can ISO7241 and ISO6741 be pin to pin?

  • 0 in reply to Lin GarHao
    TI__Genius 14645 points

    Hi Lin,

    1. Yes, you may leave pin 52 floating.

    2. ISO7241C is older generation device. The digital isolator team has come out with the ISO6741 which has higher isolation and wider supply range and should be recommended for new designs. This device is pin to pin with ISO7241. Since this is newer generation device it will have better pricing and supply. 

    Regards,

    Brandon

  • 0 in reply to Brandon Beader
    Prodigy 50 points

    Hi Sir,

    There are still a few questions here that I need to confirm with you.

    As shown below, refer to "VPWR" in the circuit diagram. If we set the power supply (VPWR_54V_PSE) to different connection pins, will there be any impact?

    Reference circuit：

    Design schematic：

  • 0 in reply to Lin GarHao
    TI__Genius 14645 points

    Hi Lin,

    IEEE802.3 spec does not govern which pairsets are positive and negative, it only matters for the channel connection. For instance, pairs 1/2 and 3/6 is a channel. It does not matter is 1/2 is positive or 3/6 is positive as long as the return is the alternative. 

    The same goes for 3/4 and 7/8. Does not matter if 3/4 is positive or 7/8 is positive as long as the alternative is your return. You can NOT use 1/2 are your 54V and then use 3/4 as your return.

    I was unable to find that data transformer to check the actual wiring. Ensure my above statement is true when connected on the port.

    Regards,

    Brandon