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AFE78101: Relation between VREF & VOUT

Yogesh Nadarge
Prodigy 110 points
Part Number: AFE78101

Tool/software:

Hi, 

I'm planning to use AFE78101 in my device. When I looked into datasheet, found out that Vref=1.25V where as Vout is upto 2.5V. Normally Vout is same as that of Vref in DAC. 

What is the relation between Vref & Vout in this case? Also which one I should consider for resolution calculation

Thanks,

Yogesh

  • 0
    TI__Mastermind 42203 points

    Hi Yogesh,

    This device has selectable output ranges. See the options along with the transfer function in the below screenshot. 

    Resolution is 14-bit. Your step size would be the selected FSR from table 7-2 divided by 2^14. if you choose the 0.3V to 2.5V output range, make sure to use 2.2V as the FSR in your resolution calculation, because the minimum output voltage is 0.3V

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 110 points

    Hi Katlynne, 

    Thanks for the response. If I want to generate the Vout to be 0.912 V for PVDD>2.7V & DAC,_CFG.RANGE as 0 then what will be the value of DAC_GAIN in above formula? Is it possible to generate it?

  • 0 in reply to Yogesh Nadarge
    TI__Guru* 97855 points

    Yogesh,


    The DAC_GAIN is a scaling factor that you would use to change the full scale range of the DAC. Normally you would leave this to be 0x8000.

    With DAC_CFG.RANGE set to 0, and the PVDD at 2.7V, The VOUT range would be 0.3V to 2.5V. Then you would calculate where on the scale 0.912V is. Subtracting the VMIN voltage of 0.3V, the scale from the range would be 0.612V out of 2.2V. To get this voltage, you would use this equation:

    DAC_DATA/2^14 = 0.612/2.2

    DAC_DATA = 4558d = 11CEh


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 110 points

    Hi Joseph Wu,

    Thank you for the explanation!