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OPA928EVM: OPA928 integrator reset

Daniele Paesani
Prodigy 90 points
Part Number: OPA928EVM
Other Parts Discussed in Thread: OPA928, LMP7721,

Tool/software:

Hello, 

on the SBOU282A document for the OPA928 (section 4.2.2.1) the integrator is reset via Omron G3VM-81PR(TR05) MOS FET relays. 

For the aforementioned usage of the evaluation kit, I would like to understand which specifications can be expected (or were measured) in terms of

1) leakage current on the bootstrapped solid state relay K2

2) charge injection during the reset operation.

Thank you and best regards, 

DP

PS. i am also interested in the LMP7721, but I am not able to find a curve of Ibias vs temperature (similar to the one contained in the OPA928 datasheet, first page)

  • 0
    TI__Guru* 77541 points

    Hi Daniele,

    Daniele Paesani said:
    1) leakage current on the bootstrapped solid state relay K2

    The leakage current in K2 relay is approx. 20pF, parasitic capacitance is up to 8pF and insulation resistance is from 1MΩ to 1GΩ (10^6 MΩ may be a typo for a typical R, if max. R = 1GΩ). 

    Here is the simulated circuit. I think that OPA928EVM's section 4.2.2.1 explain the circuit fairly clearly. I added another switch to discharge CF integrator (without it, CF may discharge longer). 

    1738.OPA928 ff_Is 01022024.TSC

    Daniele Paesani said:
    2) charge injection during the reset operation.

    The charge injection refers to the K2's leakage current, shown in Figure 4-4. 

    Daniele Paesani said:
    i am also interested in the LMP7721, but I am not able to find a curve of Ibias vs temperature (similar to the one contained in the OPA928 datasheet, first page)

    LMP7721 is supported by LVA application team, I can transfer you to the team if you have additional question. 

    LMP7721 does not have the Ibias vs. Temp plot. In CMOS technology, a common rule of thumb is that the bias current roughly doubles for every 10C increase in temperature. 

    If you have other questions, please let me know. 

    Best,

    Raymond