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Original question:

ADS8688AT: Regarding input voltage range for an ADC

ADS8688AT: Idvdd_dyn in datasheet

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Genius 10860 points
Part Number: ADS8688AT

Dear team,

Our team is using ADS8688ATDBT in our designs, and we have some questions about the Idvdd_dyn parameter in the datasheet.

 

Datasheet is stating Idvdd_dyn=0.5mA when output is 0000h. Is this "dynamic" or "static" current? If this is dynamic current, what is static current for DVDD rail?

 

We are trying to calculate worst case power dissipation for DVDD rail. We would think Pdiss_dvdd=Pstatic+Pdynamic=3.3*Idvdd_static+3.3^2*f_sclk*(Cpin+Cload), where Cpin is 5pF according to the datasheet?

 

Please advice.

 


Best Regards,
William

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    TI__Mastermind 45285 points

    Hi William,

    The digital supply (DVDD) power on the ADC is mainly consumed by output data on the SDO, the actual current depends on frequency of SDO transitions and it can be calculated by IDVDD = CSDO*DVDD*f, where CSDO is the load capacitance on SDO including capacitance on pins and trace, f is the frequency of transitions (transitions and cycle time) on the SDO.

    Back to your questions:

    IDVDD_DYN=0.5mA in the ADS8688AT datasheet is a dynamic IDVDD current under a special condition where the output code on the SDO are 0000h.

    The static/standby/power-down IDVDD current is pretty small because the device is in static/standby/power-down condition and also no transitions on the SDO line. The datasheet does not provide a guaranteed current consumption specification for DVDD at these conditions, however the IDVDD under standby or power-down is typically around 1uA.

    Below is an example how to calculate DVDD supply power on ADCs:

    You can find the details from TI Precision Labs - SAR ADC power scaling session (page 9-11).

    Regards,

    Dale