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IVC102: Larger external capacitor for IVC102

Santiago Beron1
Prodigy 20 points
Part Number: IVC102

Hello:

I want to use the IVC102 with an external capacitor a lot larger than what is usual for this IC. I want to use a 10 nF external capacitor, so I can collect more current from the sensor that I am using. None of the charts in the datasheet go beyond 1nF.  The questions that I have are:

1. What could be the issues with using such a large capacitor?

2. During reset, could this larger charge damage the S2 switch due to a more prolonged high current? I understand reset tie will be longer. No problem. 

3. What about linearity of the measurements?

Regards

Santiago

  • 0
    TI__Mastermind 49926 points

    Hello Santiago,

    The quality of the external integration capacitor strongly affects performance.

    Some of the more critical parameters include: voltage coefficient, temperature coefficient and dielectric absorption. The voltage coefficient of the capacitor introduces nonlinearities which degrade INL. The temperature coefficient produces gain error drift over temperature. Dielectric absorption can degrade performance for higher frequency input signals and also affect linearity.

    Capacitor related leakage current could be an issue if it is significant relative the current level being integrated.  The section Choosing CINT  of  the data sheet discusses the types of capacitors best suited for the external CINT. A large external capacitor will swamp the much smaller internal capacitance and will dictate the capacitor's contribution to the circuit's behavior.

    The fundamental operation of the IVC102 should be maintained despite the large externa integrator capacitor. 

    What is the current range in your application? Are you planning to use in basic reset and integrate measurement mode or switched input measurement technique?

  • 0 in reply to Praveen Aroul
    Prodigy 20 points

    Thank you Praveen.

    I am using the basic reset and integrate measurement mode. I want to integrate current in the range of 400nA for up to 300 ms.

    Would the internal reset switch be capable of handled the higher current discharge of a larger (10 nF) capacitor?

    Regards

  • 0 in reply to Santiago Beron1
    TI__Mastermind 49926 points

    Hello Santiago,

    Based on the input current range section of the datasheet, it seems like the switch should be able to handle 400nA current.

    Since you are using 10nF, you may have to increase the reset time to possibly 200-250us by extrapolating from the reset time vs Cint curve.