Does anyone have any information on temperature hysteresis for the internal voltage reference on the AD7795 ?
Internal Reference Drift is the specification we used to describe how the reference output voltage will drift over a given temperature. For AD7795 the typical drift for the internal band gap reference is 4ppm/degC. May I know what is your application and what is the target specifications and operating temperature range of your system?
Our system has to operate to +100 Deg C. The system is calibrated at room temperature. We are seeing offset errors at temperature in excess of those calculated from information in the datasheet. Heat cycling the assembly seems to reduce this error. I was wondering what is the magnitude of the initial voltage reference shift?
Calibration can be used effectively to remove any errors associated with temperature drift. Self-calibration will remove the effects of temperature drift within the ADC itself. Are you going to operate at +100degC only? If yes, can you calibrate the ADC at that temperature instead of room temperature?
I know about self calibration but the offset reduces with heat cycling. The system needs to operate to +100DegC not just at. I am wondering if the cause could be stress in the PCB assembly, but was after the initial voltage reference shift and hysteresis so I can rule these out also.
We did not measure the hysteresis on the internal reference. You are correct about soldering will put stresses on the package which can affect the reference specification. If the reference tempco is measured after soldering, then 2 forces are at play – the reference drift and also the de-stressing. If the board is allowed to sit for several 100 hours after soldering, it will de-stress naturally. Temperature cycling the part after soldering will speed up the de-stressing process. So, you could heat the board to 100 degC and hold it at this temperature for a period of time. This will remove the stresses due to soldering and the tempco for the internal reference will then be within the datasheet specification.
Retrieving data ...