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ADS1262: chop mode and latency conversion time

Felice Bonardi
Prodigy 50 points
Part Number: ADS1262
Other Parts Discussed in Thread: TIPD188, ADS1261

I'm working on a design to read bridge sensor 350Ohm, supplied at 5V, with a full scale of +/-10mV.

I'm planning to use the ADS1262, in similar configuration described in TIPD188, using the AC mode available with chop mode register.

I've not clearly understand the chop mode function.

My application need to have the following configuration:

- 7200SPS,  SINC1 --> 2310Hz bandwith

- td(STDR) = 0.494ms

- DELAY[3:0]=278us

In this condition in single convertion mode (DC) I will reach 1/(0.494ms+0.178ms)= 1295SPS, NOT 7200SPS.

In this condition in single convertion mode (AC) I will reach 2/(0.494ms+0.178ms)= 647SPS, NOT 7200SPS.

For my application 647SPS could be enough, but which in the -3dB bandwidth and the ENOB?

What append if I set the continuous conversion with the chop mode enabled? I don't understand who drive the output pin to reverse the power supply of the bridge, as shown in the TIPD188.

In order to reduce the CPU load of the microcontroller, I plan to read the ADS1262 with a timer of 600Hz and I prefer the the ADS1262 will manage by itself the chop mode. Do you think that there is a way to do it?

Regards

Felice

  • 0
    TI__Mastermind 44600 points
    Hi Felice,

    Welcome to the TI E2E Forums!

    Just for clarification, are you trying to chop the ADC input, or are you trying to implement ac-excitation (chopping the bridge)?

    On the ADS1262, it can chop the ADC inputs and perform the averaging calculation for you; however, when performing ac-excitation you need to average the results....In case you're looking to perform ac-bridge excitation there is a new ADC, the ADS1261, which can manage the ac-excitation mode by itself.

    Regarding the data rates, since the ADS1262 uses a SINCx digital filter you'll find that chopping or ac-excitation is actually much slower than the ADC's continuous conversion data rate. The reason for this is that the SINCx filter is very much similar to a moving average filter that averages "x" samples. When you begin converting, you have to first fill up the filter with "x" results before the moving average is accurate; however, from then on the moving average can update with each new conversion.... Now when you start chopping the inputs, the moving average filter resets between conversion results, so it actually takes 2 times "x" samples to compute the moving average of the two different input signals, and then each new result thereafter requires another "x" conversions before the "average" of the "moving averages" can be computed.

    Therefore when you multiplex, chop, or use ac-excitation along with a SINC filter, you typically need to select a data rate that is much faster than the expected throughput.

    I hope that helped. Please let me know if you have any additional questions!

    Best regards,
    Chris