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TMS320F28379D: microcontroller clip the -ve part of signal

Gerald
Genius 9570 points
Part Number: TMS320F28379D
Other Parts Discussed in Thread: ADS8688AT

Hi Team,

May I ask for help? Our customer have a concern: I am working with C2000 Launch Pad XL TMS320F28379D (VER: 2.0). This microcontroller clip the -ve part of signal, when i give input to the ADC. So i want a microcontroller which can pass -ve part of the signal too

I am sending sine wave using waveform generator to ADC. Without giving any offset to the signal, i want to extract the analog signal from DAC which is giving to the ADC.
0284.attachments.zip

Can we use differential input to ADC for signed signal and extract the signed signal from DAC?

Kind regards,
Gerald

  • +1
    TI__Guru 60865 points

    Hi Gerald,

    You'll need to add some offset somehow.   Differential input still requires both the positive and negative input pins to be between VSSA and VREFHI.  See "Figure 7-29. Differential Signaling Mode" in the device datasheet.  https://training.ti.com/node/1139103 might also be a helpful resource.  

    If you don't want to use any signal conditioning circuits, you'd need an ADC with "bipolar" inputs.  For instance, https://www.ti.com/product/ADS8688AT. 

      

  • 0 in reply to Devin Cottier
    TI__Genius 9570 points

    Hi Devin,

    Thank you for your response. I have forwarded your response to our customer and will initially tagged this case as resolved. We will let you know if we need further help.

    Kind regards,
    Gerald

  • 0 in reply to Gerald
    TI__Genius 9570 points

    Hi Devin,

    Please be informed that I got a response from customer. Our customer is using MATLAB/Simulink for dumping the control logic to C2000-TMS320F28378D Launchpad. The Signal is Analog in nature which is converted through ADC. Then he wants the signal again in analog in nature so he put DAC as shown in Figure.

    Customer is asking: So the question is how can we use this ADS8688AT for my analysis?, will DAC is also required bipolar in nature?

    We hope you can further support us and thank you so much for your advises.

    Kind regards,
    Gerald

  • +1 in reply to Gerald
    TI__Guru 60865 points

    Hi Gerald,

    ADS8688AT was just an example of a bipolar ADC.  

    If you want to sample a bipolar input signal using an F2837x device, you'll need to use some signal conditioning circuits to add an offset (and potentially scaling) before sampling it with the F2837x ADC.  Similarly, if you want to use the buffered DAC on the F2837x device to re-create a bipolar signal, you'll need to add some offset using signal conditioning circuits (and possibly some scaling). 

    If you want to use something other than F2837x ADC and DAC, you'd need to get an MCU with bipolar ADC and DAC (as far as I know, this doesn't exist or at least is extremely uncommon).  Otherwise, you can get an external ADC and DAC (like ADS8688AT, but use the part selection tool based on your needs: ADC: https://www.ti.com/data-converters/adc-circuit/precision-adcs/products.html#p3093min=-12.5;-3.3, DAC: https://www.ti.com/data-converters/dac-circuit/precision/products.html#p1693min=-40;-3.3 ).  You'd then need to connect the external data converters to your device and write SW to communicate with them.