• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 326 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.

TCAN1043A-Q1: wake PIN question

qinlei
Intellectual 430 points
Part Number: TCAN1043A-Q1

Tool/software:

hello, 

i checked the TCAN1043A-Q1 , I will apply the local wake up pin 

when i apply the High side control, I don't understand the meaning of the following formula

The formula is explained in the specification book, but I didn't understand it

As shown in the figure below, if my maximum input voltage is 45V, as described in the specification book, then the voltage at point C in the figure is 45V. So, which point's voltage is 44V? Is it B or C? What is the voltage at point A? Is the direction of the current indicated by the red arrow? Please help explain in detail

thank you

best regards 

  • 0
    TI__Guru 53555 points

    Hi Qinlei,

    Thanks for bringing your question to E2E. 

    This formula is meant to ensure that the biasing resistor in a WAKE circuit is strong enough to drive an appropriate voltage at the wake pin even when the adaptive internal bias in providing the opposate bias. For a high-side switch configuration, we need to ensure that the pull-down resistor in series with the series resistor is capable of sinking enough current from the internal pull-up source to make the input voltage at the WAKE pin fall below the low-level input threshold. 

    Vwake = Ibias * (Rbias + Rseries)

    Our target Vwake in this case is below low-level input voltage threshold. Assuming that the internal pull-up is active, to Ibias supplied by the transceiver will be IIH. Substituting these in and rearranging the equation to solve for Rbias we get:

    Vwake = Ibias * (Rbias + Rseries) < VIL

    IIH * (Rbias + Rseries) < VIL

    (IIH * Rbias) + (IIH * Rseries) < VIL

    (IIH * Rbias) < VIL - (IIH * Rseries)

    Rbias < (VIL / IIH) - Rseries

    This is different from the form in the datasheet that is for a low-side switch configuration, which may be where some of your confusion is coming from. 

     

    Note that once the transceiver has recognized a low-level input, the internal bias will switch to a pull-down configuration to reduce system power consumption. This will also cause the voltage as the WAKE pin to rest very close to ground potential until the high-side switch is activated. 

    Let me know if this is clear and if you have any more questions. 

    Regards, 
    Eric Schott

  • 0 in reply to Eric Schott1
    Intellectual 430 points

    HAHA , I got it.I think the description in the specification is very easy to cause misunderstanding. I thought for a long time and woke up the dreamer with one word. Thank you very much~