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ADS1259 reading improvement techniques

rahul Nadgouda
Intellectual 360 points
Other Parts Discussed in Thread: ADS1259, PGA280

I am evaluating ADS1259 using ADS1259EVM. Other than taking care on the PCB  and software calibrations for getting accurate readings...I want to know whether there are any techniques on the schematic to reduce the errors in readings. I have taken care on the power supplies by providing decoupling caps and an RC filter at the i/p, and all the caps mentioned in the datasheet. Other than these...are there any other techniques?

 

 

Regards

Rahul

  • 0
    TI__Guru 55466 points

    Hi Rahul,

    From the schematic point of view, as you have already mentioned, it is important to place close to the supply pins of the supplies decoupling capacitor.  A 1uF to 10uF capactior in close proximity to AVDD adn DVDD will work well.  Figure 64 of the datasheet (PGA280 driving the ADS1259)  also shows a 1uF capacitor accross VREFP and VREFN; (the ADS1259EVM uses a 10uF capacitor) and 1uF to 10uF capacitor on the BYPASS pin.  A differential low pass filter with 47Ohm resitors and a COG grade 10nF capacitors is used in close proximity to the inputs of the ADS1259; low-pass common-mode COG capacitors of  47pF at the inputs are also shown on the ADS1259EVM.  A 1uF to 10uF is also used going from the ADS1259 REFOUT pin to the VOCM pin of the PGA280.  If you plan to use a external reference, you may consider providing a quiet, low drift voltage reference such as the REF5025 and a low pass filter in the same fashion as shown on the ADS1259EVM.  You may also consider using an external crystal as shown on the EVM if you are concern about 50/60Hz NMRR rejection since the data rate and corresponding notches scale by the accuracy of the clock frequency.  Depending on the signal you are measuring;  you may also consider low-pass filters at the inputs of the PGA280.

    It is also very critical to have an optimal board layout and grounding.  In general, you want to have an appropiate ground layer on the board and avoid crossing the digital and analog signal paths to reduce noise.  I recommend to go through  the general layout "Design Notes- General PCB Layout Questions" recommedations given on the link below and also using the ADS1259EVM board layout shown on the user's guide as an example.

    http://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/general-pcb-layout-questions.aspx

    Thank you and Best Regards,

    Luis