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TMS320F28377D-EP: About 16bit ADC

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Guru 21045 points
Part Number: TMS320F28377D-EP
Other Parts Discussed in Thread: AMC1300B-Q1, , TINA-TI, AMC1300

Hi Team,

 

We would like to sense the motor current by AMC1300B-Q1 and 16bit ADC of TMS320F28377D-EP.

Could you please let us know if you have recommended design method and ROUT, COUT values?

 

[My idea]

I understand that sample window duration (set by ACQPS and PERx.SYSCLK) is 320ns(min).

Therefore, we set the output filter(ROUT and COUT) to be “less than 320ns” so ROUT=36Ω and COUT=330pF.

 

<Circuit image>


 

 

Regards,

Hide

  • 0
    TI__Guru 60865 points

    Hi Hide,

    We now have an app. note + TINA-TI files to help with this task here:   

    We don't go into any detail for differential designs in the app. note, but the same principles apply and we do provide a differential simulation setup in the included TINA-TI files.  

    The starting point for Cout would be 20 x Ch = 20 x 16.5pF = 330pF, so you are right on recommendations for this one.

    Rout is usually determined via simulation, but the analog engineering calculator can give you a starting range:  

    Things get a little ugly though when looking at the AM1300B output bandwidth, which is only ~300kHz.  You may find the required settling time to 16 + 1 bits of resolution excessive because of this.  You can either add a differential buffer after the AM1300B, or it may be possible to use a charge-sharing input design if the sample rate on this channel is sufficiently slow.   

  • 0 in reply to Devin Cottier
    Guru 21045 points

    Devin-san,

     

    Thank you for kind support and detail information.

    Your comment was helpful.

    > Things get a little ugly though when looking at the AM1300B output bandwidth, which is only ~300kHz. You may find the required settling time to 16 + 1 bits of resolution excessive because of this.

     

    Do you have a track record of using the combination of AMC1300B(or AMC series) and 16bit ADC of TMS320F28377D-EP?

    If yes, could you please let us know the information?

     

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Guru 60865 points

    Hi Hide-san,

    I don't have any additional specific information about AMC1300 + C2000 16-bit ADC.  However, it looks like the AMC1300 has an available TINA-TI model, so you should be able to fully evaluate the ADC settling performance using the methodology in the previously provided app. note.

    What is the intended sample rate on this channel? 

  • 0 in reply to Devin Cottier
    Guru 21045 points

    Hi Devin-san,

     

    I confirmed sample rate.

    -If 16bit ADC, 1,1MSPS (sample hold time 320us)

    -If 12bit ADC, 3.5MSPS (sample hold time 75us)

     

    So, we would like to use the max spec of TMS320F28377D-EP.

     

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Guru 60865 points

    Hi Hide-san,

    Ok.  In that case you are going to need to build an op-amp drive stage between the AMC1300 and the C2000 ADC.  You can use either a single fully-differential op-amp or a pair of single-ended op-amps.  The previously linked app. note should help with op-amp bandwidth requirements and sizing of the capacitor and resistor at the drive stage output.  

  • 0 in reply to Devin Cottier
    Guru 21045 points

    Hi Devin-san,

    Thank you for always kind support.

    I greatly appreciate your cooperation.

    Regards,

    Hide