• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 164 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS23861: About IDET

Charlie Xiao
Expert 7545 points
Part Number: TPS23861

Hi team,

I have two questions that I don't understand.

1. In 802.3at, when to use Alternative A (1236) of twisted pair and when to use Alternative B (4578)?

2.In TPS23861, 

When will IDET=540uA appear? Thanks.

Best Regards

Charlie Xiao

  • +1
    TI__Genius 15275 points

    Hi Charlie,

    Please see my responses below. 

    1. IEEE802.3at standard defines the twisted cable pairs in two different configurations Alt-A and Alt-B. Alt-A is pair 12-36 and Alt-B is 45-78. The difference is Alt-B are considered the "spare" pairs. There is no hardware difference between Alt-A and Alt-B just that per standard Alt-A is typically used since Alt-B are "spare" pairs and mostly only used for data. Please also note TPS23861 only supports Alt-A configuration.

    2. IDET is the detection current under different test conditions. IDET=540uA this is high current detection point where Vvpwr - Vdrain = 0V.

    Very Respectfully,

    Brandon Beader

  • 0 in reply to Brandon Beader
    TI__Expert 7545 points

    Hi Brandon,

    Thank you for your answer.

    I would like to ask if IDET=540uA occurs only when the port is short-circuited or the port resistance is extremely small. Thanks.

    Best Regards

    Charlie Xiao

  • +1 in reply to Charlie Xiao
    TI__Genius 15275 points

    Hi Charlie,

    IDET=540uA occurs when during 4-point detection, the first measured resistance is <2k (Open Circuit/Low Resistance), then we sink 540uA since higher current provides higher degree of accuracy for Low R.

    Very Respectfully,

    Brandon Beader

  • 0 in reply to Brandon Beader
    TI__Expert 7545 points

    Thanks Brandon.

    Best Regards

    Charlie Xiao