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ADS1240 - Conversion time from Standby

D. Johnson
Intellectual 700 points

I have an battery powered application that requires very low standby currents.  Only one differential channel is required to the input mux will not be switched.  My plan is to power up the system, run a calibration cycle on the ADC and put the device in standby.  I would like bring the device out of standby, take a sample, go back to standby. 

PGA = 16,   4.9152Mhz Xtal for ADC clock, single channel.

The real reason for the questions is to properly calculate the amount of power required by the system with a 5Hz sample rate.  So if there is an easy way to calculate the power, that would be valuable information.

Now, the questions -

How much time is required to come out of standby, sample the analog signal, go back to standby ?

Is a settling time or recovery time required or suggested when coming out of standby ?

Is there a suggested software flowchart describing the steps (commands) required to do this most effectively ?

Will the ADC have max ENOB after one sample cycle or are multiple cycles required for maximum performance ?

 

 

  • 0
    TI__Guru** 113765 points

    D. Johnson,

    No easy way to calculate power.  You need to add the digital and analog currents as shown in the spec tables and in the graphs at the bottom of page 8 of the datasheet.  A lot of times it is easier to measure them, but that doesn't help in the planning stages.

    A couple of ways to accomplish the slepp task.  One way is to use the power down pin.  In this case you would set the power down pin low to enter power down, then raise it high and take a reading, then go low again.  In theory the first reading should be valid, but I have no specifics on the timing of powering up the analog portion.  You might want to discard the first reading or two.

    The other way is to use the SPI commands for SLEEP and WAKEUP.

    Unfortunately there is not a lot of characterization data taken for the sleep and power up conditions.  I would guess that it would be about the same as the RESET which is 16 tosc periods.

    Best regards,

    Bob B