AD8251, AD8253 Model Convergence

Hi,

I am attempting to use the AD825x devices as current sense and voltage sense instrumentation amplifiers in an analog control loop. I was unable to get the SPICE models for the AD825x to work with PSpice and LTSpice. While the circuit simulation was stable with an approximation of the AD825x (gain followed by a low pass filter), the actual circuit when built was not stable.

I understand that my approximation of the gain/phase response of the instrumentation amplifier was not detailed enough, the frequency response of the devices is critical to the stability of the circuit.

I need some help getting a basic circuit to converge with the actual devices. I have built a simple model below; however this model does not converge.

I get the following error (The full SPICE output is attached):

  These supply currents failed to converge:

    I(X_U1.EREF1)             =   -10.00GA  \   -10.00GA

    I(X_U1.EPSB1)             =   -10.00GA  \   -10.00GA

The basic idea of the application is shown below:

Any help would be appreciated. Thanks!

Igor

Trans.out.zip
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  • 0
    •  Analog Employees 
    on Feb 1, 2016 12:06 AM

    Hi Igor,

    Good day!

    AD825x SPICE models were tested in different simulation engine and one of them is PSPICE. I also ran a quick simulation base on your attached schematic and mine works fine. I ran a 1000ms time domain (transient) response for this circuit (all sims options are defaults). If you're still unable to converge your circuit, I suggest you try GMIN Stepping in the options, try raising ITL1 to 500, RELTOL to 0.01. Relaxing the simulation tolerances/limits can ease up the machine to run your simulation.

    Regards,

    Phil

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  • 0
    •  Analog Employees 
    on Feb 1, 2016 12:06 AM

    Hi Igor,

    Good day!

    AD825x SPICE models were tested in different simulation engine and one of them is PSPICE. I also ran a quick simulation base on your attached schematic and mine works fine. I ran a 1000ms time domain (transient) response for this circuit (all sims options are defaults). If you're still unable to converge your circuit, I suggest you try GMIN Stepping in the options, try raising ITL1 to 500, RELTOL to 0.01. Relaxing the simulation tolerances/limits can ease up the machine to run your simulation.

    Regards,

    Phil

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