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AFE0064: Reset levels

Diego Gallardo
Prodigy 20 points
Part Number: AFE0064

Hi there,

In the datasheet it specifies that the integrator's positive input voltage is 1.68V

However, the reset levels are either REFM or REFP (depending on up/down integration). I f I understood correctly, the integrator should be able to use the complete ABS(REFP-REFM) voltage range for the output.

How can this be the case if the OA positive input voltage is 1.68V? Is the integrating capacitor discharged completely during reset? or is it preset to REFM/REFP?

Thank you very much in advance!

  • 0
    TI__Prodigy 620 points

    Hi Diego,

    The input common mode of the integrator is 1.68V. The inputs IN<0 ... 63> will also maintain same input common mode under normal operating conditions.

    The integrator architecture is such that, its reset level output is REFM (integrate-up) or REFP (integrate-down). The integrator uses complete voltage range ABS( REFP - REFM).

    As you rightly said, the device internally presets feedback capacitors to appropriate voltages ensuring there is no additional charge due to different input-output common mode.

  • 0 in reply to Shriram Devi
    Prodigy 20 points

    Hi Shriram,

    Thank you very much for your reply!

    "the device internally presets feedback capacitors to appropriate voltages" - Thanks for the clarification, as that is not shown on the schematics in the datasheet.

    I am trying to build an approximate model of the integrator stage of the AFE in Cadence, so that I can design and tweak an interface circuit to a sensor. Is there any way in which you could give me a hint as of how the presetting of the capacitors is done? That may help me specify required voltages and current for the interface circuit.

    Best regards,

    Diego

  • 0 in reply to Diego Gallardo
    TI__Prodigy 620 points

    Hi Diego,

    To keep diagrams simple, we have not shown these details in the datasheet. Also, these details don't affect the device operation.

    I guess, you are interested in simulation model for signal processing, noise etc. In such case, you can simply consider input voltage levels as ground (or REFM). The output then can swing from zero (or REFM) to REFP.