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ads1256

adeboye christopher
Prodigy 10 points
Part Number: ADS1256


I am using an ads2256 converter. I have successfully interfaced with my controller, enabled  relevant settings and all. However, when the input buffer is enabled, the adc readings  go outside of the fsd set through the pga. When exactly is the best time in the conversion process to enable/disable the input buffer?

At the moment I switch the buffer on or off before changing the mux bits. I previously tried enabling/disabling the buffer after mux selection before pga confoguration,  but the results are the same. I read mostly negative values on single-ended inputs.

The usage of the adc involves setting channel-specific configurations in the pga and buffer subsystems.

Kindly enlighten.

  • 0
    TI__Mastermind 44720 points

    Hi adeboye christopher,

    Welcome to the TI E2E Forums!

    Enabling the PGA reduces the input rage of the ADS1256, so it is typically something you'd want to set ON or OFF, depending on the expected input signals you expect to measure. There is the ADS1255-7 Design Calculator which can help you determine if an input signal is outside of the PGA's input range.

    If you make a change to the register settings, such as turning the PGA ON or OFF, it usually recommended to start a new ADC conversion (using the SYNC and WAKEUP commands), so that you do not get an unsettled conversion result (the digital filter is computing something like a moving average of the input signal during the conversion period, so step changes to the input signal will not be fully resented in the output data of the Delta-Sigma ADC).

    If you need a wider input range and a buffer, then I would either consider a different ADC with different input range requirements, or perhaps an external amplifier/buffer with the appropriate supply voltages (for example, if you need to input a 0V signal, most amplifiers will require a -300 mV negative supply to allow the output to drive to 0V without saturating).