• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 82 subscribers
  • Views 285 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.

TMS320F280025: ADC internal circuit questions

Emma Wang
Expert 5210 points
Part Number: TMS320F280025


Expert,

I want to ask a question on internal circuits for ADC module for F280025.

Customer use CT to sample the L current and there will some minus voltage happens, and may above -0.3V.

and we have a restrict on -0.3V input voltage.

however, customer told me, there seems more margin for F2803X input voltage. Did we changed some thing for ADC design?

On the other hand, do we have internal clamp diode for ADC pin?

BR

Emma

  • 0
    TI__Mastermind 42195 points

    Emma,

    Emma Wang said:
    however, customer told me, there seems more margin for F2803X input voltage.

    On both devices the absolute maximum rating is -0.3 to 4.6 for input pins, there is no change.

    Emma Wang said:
    Did we changed some thing for ADC design?

    Yes, both devices have entirely different ADCs.

    Emma Wang said:
    On the other hand, do we have internal clamp diode for ADC pin?

    Yes, Analog inputs still have a clamping diode. The clamp current is in that table.

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    TI__Expert 5210 points

    Hi Cody,

    Thanks for your reply. another questions, did we need to remove the external clamp diode since we have an internal clamp diode? if we add an external clamp diode, what side effect will bring?

    BR

    Emma

  • 0 in reply to Emma Wang
    TI__Mastermind 42195 points

    It is OK to have an external clamping diode. Please note that the internal clamping diode will have a relatively low current limit.

    If you have an external clamping diode it is important to know where the current is flowing. If you put an external diode in parallel with the internal diode the current will be shared. And due to process either the internal or the external diode may take more of the current, it depends on the exact voltage threshold of each diode.

    A resistor or low pass filter placed between the diodes can help bias the current flow towards the external diode.

    Regards,
    Cody 

  • 0 in reply to Cody Watkins
    TI__Expert 5210 points

    Cody,

    Thanks and got it.

    However, customer use CT to sense the current and the minus voltage may happen.

    Below is their schematic.

    I just want to know. whether we have a recommend on how to add diode in this scenario (minus voltage may happen).

    since customer told me there is only very small minus voltage, then the device broken. it happens so many times in their test.

    BR

    Emma

  • 0 in reply to Emma Wang
    TI__Mastermind 42195 points

    Emma, yes you should apply some sort of clamping diode to keep the voltage from going below VSSA.

    You can see something similar mentioned here. https://e2e.ti.com/members/1120590

    Regards,
    Cody