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MSP430FG437 DAC12 Offset Calibration Question

Mike Marks
Prodigy 140 points

The datasheet for the 4-series family of devices gives limited information on the calibration of the offset for the 12-bit DAC.  It mentions how to calibrate the offset (set a bit and wait for it to be cleared), but does not mention how often one needs to calibrate or how long the calibration should take.  Is there another application note that might provide these answers? Also, does the calibration need to be performed periodically, or is once at start-up sufficient?  Does it need to be calibrated any time the front end gain is changed?

Thanks,

Mike Marks

NDI Medical

  • 0
    TI__Prodigy 130 points

    The calibration for the 12-bit DAC should be done before performing a first conversion.  This is done via the DAC12CALON bit.  If the DAC is disabled or the device is reset, then the calibration should be repeated.  It is good practice to repeat the calibration again if the front end gain is changed.

  • 0 in reply to Jennifer Barry
    Prodigy 140 points

    Many thanks for the answer on when to calibrate.  Do you have any information about how long the calibration cycle takes?  Are we talking a few clock cycles, a few msec or hundreds of msec, etc.?

    Thanks

     

     

  • 0 in reply to Mike Marks
    TI__Prodigy 130 points

    The calibration of the DAC12 is running on SMCLK of the device for the 4xx generation.  In the datasheet for each device, there is an estimated calibration time depending on the DAC Amplifier setting (DAC12AMPx).  This is normally in msec ranging between 6 to 100 msec maximum value. 

  • 0 in reply to Jennifer Barry
    Prodigy 10 points

    Can both DACs on a F1611 be calibrated at the same time or must I do them consecutively?

  • 0 in reply to Tom Decker
    Guru 227245 points

    From the 1611 users guide:

    For best calibration results, port and CPU activity should be minimized during calibration.

    So I guess, doing a second calibration at the same time should be avoided too. The PSRR is 70dB only, while the dynamic range is 72dB. So anything that influences the dynamic power consumption of the MSP or does affext the supply voltage in any other way will influence the LSB and therefore the offset calibration too. But it might be of no importance with a differential nonlinearity of +-1LSB max.
    A recalibration due to temperature drift might be necessary, but since the drift is only 30µV/°C and the remaining offset voltage is +-2.5mV, it must be a temperature change of many degrees before the drift reaches the magnitude of the calibrated offset error.
    Also, the calibration does not correct the gain error.

    The calibrtion times range from 6ms for high-current mode to 100ms for low-power, slow-settling mode.

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