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AD8251, AD8253 Model Convergence

Question asked by Igor_M on Jan 29, 2016
Latest reply on Apr 19, 2017 by liubenyuan

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

 

AD825x_sim.PNG

 

 

The basic idea of the application is shown below:

AD825x_Loop.png

Any help would be appreciated. Thanks!

Igor

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