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ADS131M02: How is the response time calculated

HE
Intellectual 295 points
Part Number: ADS131M02

helllo:

There are two questions,  hope you can help me,

Question 1     How is the response time calculated?

The default configuration： data output rate is 4K ，external crystals is 8.19Mhz

When there is an excitation input, such as 1V, how long after the ADC output data will remain stable?

Question 2     Is it feasible to read the data periodically?

The default configuration： data output rate is 4K ，external crystals is 8.19Mhz

For example, read the value every 300us (read only once). Is the data real time, or is it 300 milliseconds old?

  • 0
    TI__Mastermind 18900 points

    Hello HE HE,

    HE said:
    Question 1     How is the response time calculated?

    Output data rate = sample rate. So if we have 4k = f_sample = 1/t_sample. t_sample = 1/4k = 250us. If the first sample you read is t = 0, then every subsequent sample is +250us from the last one. The important part here is that DRDY determines when the actual sample was completed and processed. So, if you trigger on the falling edge you can calculate the delay from the to where you actually grabbed the data you should be able to figure out when the sample was actually taken (which sort of answers your second question).

    There's a bit of a problem with this philosophy though. Delta sigma ADCs inherently average where SAR ADC are what you should use if you want a snapshot of what the signal is doing in time. You'll need to consider if this averaging works for your application. This is covered in this TI Precision labs (TIPL) video: https://training.ti.com/ti-precision-labs-sar-delta-sigma-basic-operation?context=1139747-1140267-1128375-1147914-1147913 

    HE said:
    Question 2     Is it feasible to read the data periodically?

    Yes, according to the datasheet, you'll have less than 500us = 2*250us (2*t_sample) to get the data. With SPI clock going up to 25MHz (1/40us), you 

    Reading every 300us is arbitrary, you should really be reading every time DRDY toggles and using it to trigger an interrupt. Also, if you ever skip a sample you'll need to clear the FIFO because DRDY behavior will be unpredictable. 

    Best,

    -Cole