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ADS1220 sampling rate

JUN SHIN
Prodigy 30 points
Other Parts Discussed in Thread: ADS1220

Hi,

I have one more quick question regarding ADS1220. 

I use it in Normal mode at 1ksps data rate (continuous mode), and I use its own internal oscillator.

I expected that the delta between consecutive DRDY_  falling edges would be exactly 1ms,

but I found that it was actually 1.01ms or 1.02ms on Oscilloscope roughly. 

Other sensor that I am using along with ADS1220 gives exactly 1ms of period when set to 1ksps. 

What would be the reason for this 1 - 2% of difference, and how can I improve the accuracy?

Your help will be greatly appreciated. 

  • 0
    TI__Guru** 113765 points

    Hi Jun Shin,

    The accuracy of the internal oscillator will typically vary +/-1% but can vary by as much as +/-2%.  This information is given on page 6 of the datasheet in the Electrical Characteristics table.  This has a direct relationship to the output data rate.  Also note that the data rate values expressed as nominal are rounded off to a more readable number.  The true conversion times are expressed in Table 11 on page 27 of the datasheet.  The true data rate for the nominal 1000 sps is 988.4 sps.

    The range that can be observed from device to device will be 1008.2 sps to 968.6 sps.  The values you are seeing are within this range.  If you need improvement, then you will need to provide an external clock to the CLK pin of the ADS1220.  The data rates as shown in the datasheet match the external clock frequency of 4.096MHz.  You can apply an external clock from a variety of sources.  You might use a clock output pin from a microcontroller or a dedicated oscillator as example clock sources.  If you want to apply an external clock and achieve a true 1000sps data rate your clock source would need to be 4.144MHz instead of 4.096MHz.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 30 points
    Thanks for your prompt and detailed explanation.