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INA200: What is the input impedance of the VP and Vn pins?

Bhaktprakash Patel
Prodigy 70 points
Part Number: INA200
Other Parts Discussed in Thread: , INA193

1. What is the input impedance of the VP and Vn pins?  

2. I have a Vbatt of 8V, and my design's aim is to current sense. I am feeding 3.3V to the INA200. What is the danger that 8V appears across Vp, Vn pins when Vdd is coming up to 3.3V? Data sheet claims under this situation ensure current going into the diff. input pins remains at < 5mA, how can I confirm this? We did place a RCR network to filter the diff inputs to the IN200. 

I am having a situation where the Comp output goes to 3.23V, with a Vdd of 3.3V (I understand these are not rail to rail outputs - that's fine). The diff input is only 1.2mV, via 3mohms sense resistor -  I suspect the parts may be damaged due to case 2 listed above. The Resetn pin is low all the time. Please confirm that the Resetn pin is only for the comparitor , and not a general Resetn for the chip.

We do not understand why the INA200 is outputting 3.32V, with a diff input if 1.2mV, any idea's. This has happened over time, after about 100-200 power cycles, to (4) out of the (12) units we are testing.          

 Thanks

  • 0
    TI__Mastermind 24135 points

    Hello Bhaktprakash,

    Thanks for considering to use Texas Instruments.

    1. I need to look into this and will get back to you on it.  However, if you are looking into exceeding the common mode voltage, you will be turning on the ESD cells which will sink as much current as necessary until either they break our your common mode voltage collapses to below their breakdown voltage which is most likely near the abs max rating.

    2.  If your common mode is 8V while the device supply is ramping up to 3.3V, the device should not be damaged.  Which 5mA statement are you referencing? The one beneath the abs max table says you need to limit the current if the common mode voltage exceeds 80V or -16V.

    For 20V/V*1.2mV=24mV to trip a comparator referenced to 0.6V, it does seem like you have a damaged part.  What kind of tests are you subjecting the part to during these 100-200 power cycles?  After how many cycles do these failures typically occur?

    Reset pin is for the comparator.

  • 0
    Prodigy 70 points

    Thanks for your response.

    1. We have seen (2) parts with date codes of "TI 97". They have conformal coating on them, that's why I cannot retrieve more part, date codes. 

    The new part that we replaced on one unit has a date code of "TI 93" - and now the board works fine. Can you tell me what the numbers translate to in date wise?

      

    2. We are not planning to have > 8V common mode voltage. 

    3. We noticed  someone else had a similar issue, but I think the engineer did not get back to you, do you happen to have more details / possible resolution? 

     e2e.ti.com/.../ina200-ina200-output-at-max-vs

     

    4. If we purchase the automotive grade part INA200-Q1 - these parts claim to have lower defect rate. What is the anticipated defect rate of the standard IN200 vs the automotive grade part?  

    Thanks

  • 0 in reply to Bhaktprakash Patel
    TI__Mastermind 24135 points

    Hello Bhaktprakash,

    1. I have reached out to one of our quality engineers for the year and month those were produced.  Based off the details provided I presume these are VSSOP DGK, right?

    2. Reached out to my colleague who supported that thread and he had no other communication with that customer offline.

    4.  I looked up our FIT rates and they apparently are the same.

    You dont by chance have Vcc and Reset at different potentials do you?

  • 0
    TI__Mastermind 24135 points

    Hello Bhaktprakash,

    1.  So I have been told that the front end architecture of the INA200 is the same as that of the INA193.  Within the INA193 datasheet, there is a plot of  input bias current vs. common mode.  From this graph you can calculate the equivalent resistance seen at the input for a given common mode by dividing the common mode voltage by input bias current.

    For a DGK package the following date codes can be translated to:

    TI 93: March 2019

    TI 97: July 2019

    Previously you noted RESET pin is low all the time.  Is it soldered/shorted to ground, or are you toggling it low after the comparator triggers and that is when the comparator output gets stuck high?  I ask because we have had at least one other customer who had the comparator trip prematurely.  The cause was due to the RESET high potential and the supply potential being different.  The fix for them is placing a low pass filter on the RESET pin.  Section 7.3.3 of the datasheet talks a little about this.