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BQ32000: high time drift with temperature variation : how to reduce

F_F_S
Prodigy 140 points
Part Number: BQ32000

My problem is the drift with BQ32000DR and NX3215SA-32.768K-STD-MUA-8. The drift is -9 sec @ -30°C and -4 second @ +70°C. How Do I can reduce to 1 second/day from 0°C to 40°C and max 2 second/day <0°C or >40°C

  • 0
    TI__Genius 16845 points

    One way to reduce the drift is using the internal calibration feature. Here is a link to post describing the procedure: 

    The device would need an updated calibration value depending on temperature. This could be addressed by using a temp sensor and lookup table to set the calibration value according to the crystal's frequency/temperature characteristic.

    Kind regards,
    Lane

  • 0 in reply to Lane Boyd
    Prodigy 140 points

    Yes but if the equipment is off for example more days(run only RTC) and the temperature change from over 0 °C and under for example -20°C, I can not do the calibration...

  • 0 in reply to F_F_S
    TI__Genius 16845 points

    Thanks for the information. If I understand correctly, the BQ32000 device cannot be calibrated in your system when the equipment is off? This case would result in an inaccurate time setting when power is restored. To achieve the best accuracy, you would want to calibrate even while the system is off.

    One less accurate approach might be to try and calibrate for the average temperature. For example, your current system is -9s at -30°C and -4s at 70°C. Calibrating the device can theoretically adjust it to -2.5s at -30°C and 2.5s at 70°C. You can use the frequency/temperature characteristic to estimate how the frequency would compare between these bounds, such as where the XTAL should cause oscillation at 0ppm or min/max frequency (crystal cut will impact shape of the curve), and correlate to your range of 0°C to 40°C. If the frequency is expected to vary significantly between these points, you might need to choose a crystal with lower frequency change over the application temperature range. A drawback of this approach is it would still not ensure a level of accuracy you can achieve from calibration.

    Kind regards,
    Lane