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Original question:

TPS65911: Crystall circuit

TPS65911: How to abtain a accuracy system time with 32.768KHz crystal?

Chambin Zhang
Prodigy 165 points
Part Number: TPS65911

Hello，

We want to use 32.768KHz crystal outside of TPS65911 to calculate system time.

Our product use under -5C---50C temperature range,  we can correct crystal and system time under 25C, could you tell me how to make crystal frequency or system time accuracy under -5C---50C temperature range?

use a temperature sensor or others method?

Thanks.

  • 0
    TI__Guru* 81034 points

    Hi Chambin,

    The electrical specification in the datasheet shows the temperature effect on frequency in ppm per degree C. Alternatively an external clock could be used if you have a device that meets your accuracy requirements over temperature.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 165 points

    Hi Matt,

    I don't understande clearly about you said, did you advice to use another external clock?

    My inital idea is use a temperature sensor to measue the temerature around crystal, use temperature coefficient paramet -0.4*10^-8 to calibrate the temperature shift, do you think this idea is feasible or you have better method to solve crystal frequency change by temperature change?

    Thanks. 

  • 0 in reply to Chambin Zhang
    TI__Genius 10772 points

    Hi Chambin,

    You are trying to measure the temperature of your external crystal oscillator? 

    Chambin Zhang said:
    crystal frequency change by temperature change

    As Matt mentioned, the TPS65911 datasheet has information on the frequency temperature characteristics. If you are using an external device, then you need to look on the datasheet for that device. These should provide similar information, through numerical or graphical data.

    Thanks,
    Field

  • 0 in reply to Field Tolson
    Prodigy 165 points

    Hi Field,

    The reason why I measure the crystal temperature is there is a parameter of PMIC as follow red circle.

    My question is how to deal the temperature change effection after we calibrate the crystal under 25C temperature?

    Our product use under -5C to 50C surrounding.

    Thanks.

  • 0 in reply to Chambin Zhang
    TI__Genius 10772 points

    Hi Chambin,

    There are calculators available online that can convert ppm to Hz for you. 

    Chambin Zhang said:
    32.768KHz crystal outside
    Chambin Zhang said:
    deal the temperature change effect

    The areas you may want to research into for this:

    • temperature-compensated crystal oscillators (TCXO)
    • voltage-controlled crystal oscillators (VCXO)
    • crystal oven, or oven controlled crystal oscillators (OCXO)
    • frequency locked loops (FLL)

    Thanks,
    Field