ADS1232: Power on reset and Offset Calibration

Hi Y.Ottey,

The PDWN pin resets all of the ADS1232 device internals except the offset calibration register.  If there is an issue on power-up, there could be corrupted data in the offset calibration register.  When the self-offset calibration is issued by sending 26 or more SCLKs, the calibration procedure will correct any possible issues with corrupted data in the offset register.

It is always recommended to issue an offset calibration at power-up to remove any offset from the PGA and modulator stages.

Best regards,

Bob B

Hi Y.Ottey,

I will respond to your questions below.  I want to emphasize that the self-offset calibration is not done automatically.  The self-offset calibration can be issued at any time and should be issued on device startup, and any time the PGA gain is changed.  The self-offset calibration places an internal short that is mid-analog supply in front of the PGA.  The result should be zero, but if it is not the result is placed into internal volatile memory.  In the conversions following, the contents of the offset calibration are then subtracted from each conversion automatically.  The result that is transmitted from the device will have the corrected result.

On power-up, the contents of the offset calibration memory should start out as zero.  However, it is possible that in some conditions the power-on reset is not successfully accomplished.  Pulsing the PDWN pin with reset the device to power-up defaults accept the offset memory.  So if there is garbage data in the offset memory (we call register) then the conversion result will include this invalid data.  To correct the contents of the offset memory, the self-offset calibration should be issued.

One question that you may have is why the offset calibration memory isn't cleared on the pulsing of the PDWN pin which resets the remainder of the device?  The reason is that the primary purpose of the PDWN pin is to place the device in a low power state.  The designer did not wish to always issue the self-offset calibration each time the PDWN pin goes low and back high.  This allows the next conversion to be valid after the PDWN pin goes back high.

Now to the questions:

No.1

"It is always recommended to issue an offset calibration at power-up to remove any offset from the PGA and modulator stages."

I heard that Offset Calibration will be performed at startup. Should I perform power-on reset before that? [Bob] The self-offset calibration is not automatically performed at power-up.  The ADS1232 is a pin controlled device and the communication is from the device only.  The PDWN pin must be held low for a minimum of 10us after both the analog and digital supplies have reached nominal operating voltage.  I recommend controlling PDWN pin with a micro GPIO so that the pin can be controlled.  I also recommend that after the PDWN pin is set high and the device is operating, that the the PDWN be pulsed high-low-high to make sure that the device is in the correct operating state.  Following the pulsing of the PDWN pin, wait for the first conversion to complete and then read the conversion result sending a minimum of 2 extra clocks (26 or more SCLKs) to issue the self-offset calibration.

No.2
Is the offset (PGA, modulator, etc.) generated inside the ADS1232 held by the internal non-volatile memory?
(There was no memory notation in the data sheet.) [Bob] The memory is volatile and that is why the self-offset calibration must be issued after each power-up.

No.3
If the No. 2 question is Yes, is Offset Calibration a feature that resets the offset held in non-volatile memory?

No.4
Does the life of the IC change depending on whether Offset Calibration is used every time it is started or not? (I don't think it will change that much.) [Bob] There is no dependency on the life of the part with respect to the self-offset calibration.  If the concern is write cycles of non-volatile memory, the memory in this case is volatile and there is no write life-cycle.

Best regards,

Bob B