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INA240: Real output not linear, Spice predicted linear

Guru 39180 points

Replies: 25

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Part Number: INA240

Previous thread last two Tina models, indicate linear output via REF=GND. However the real output is not as linear and crosses 0V >-21mV. Also the idle Real 3 output/s got real quiet <6mV noise, very impressive. Oddly REF=GND is not controlling Real differential amp/s linear region as Tina Spice model indicates it does very well. Point being how can we trust the Spice results when 240 Real results do not produce the same linear output? Asked last thread what would be a better circuit configuration to produce better linear region of the entire shunt signal (REF=GND) as plots indicated possible for (-IN=510k)?

Scope capture of Real linear results below differs greatly from Spice projection! Yet output signal has the full ± (expected) signature not being produced via -IN tied directly to ground. Oddly modifying center & last sensors respectively reduced the digital output to more closely match an DC supply 100A bar (external) digital current monitor. When 3 sensors were modified (-IN=510k) the digital results were way off from external monitor digital readout and 3-240's could not detect rotor loading other than by PWM drive due to the non-linear output signal (1st,2nd captures). It would seem from Spice versus Real testing the 240 has production issues not being checked for after manufacture! Tina model used a sine wave current generator to produce excellent linear results (-IN=510k) versus Real captures below of sharp pulsed PWM signal driving the input. 

Real results CH1=shunt, CH2=240: Note shunt ± (current) signature is very much present but not so linear as Spice predicted. Note also the distinct current envelope is not broken up as via -IN=GND (last capture).

-IN=GND:

  • Guru 39180 points

    The biggest difference to note between (-IN=GND) & (-IN=510k) is the output level (V/A) reduced to 100mV, well below Spice linear prediction. The last capture CH2=700mV  actual 40mV/A=17.5A peak, 100A bar DC supply current monitor indicated 8.2A- 8.5A. Even adjusting 2mohm shunt for 3mohm, note the last capture CH2 is seemingly missing 1/2 the current cycles shown (1st/2nd) captures.

    Several plots up to 50A 3 current generator (50A) waveforms (20KHz) for -IN=510k tied to ground.

    See post below:

  • In reply to BP101:

    Hi BP101,

    The link you provided is shown as TDR archive. Can you collect the individual files into a folder and simply zip the folder?

    Regards, Guang

  • Guru 39180 points

    In reply to Guang Zhou:

    Guang Zhou
    The link you provided is shown as TDR archive

    So what is the problem,  unzip file put it in any folder and open it in Tina transient analysis plot viewer. I do this all the time with analysis plots for future reference. The plots are in order of linear output (0.5A-50A), last few plots are 3 different IN wave forms 50A current generator.

    Edit: Noticed 2mohm TDR was missing 0.5A (1st plot) 20KHz square wave (+IN signal), -IN=510k to GND. 

    Added another TDR file (noted) 5mohm shunt: /cfs-file/__key/communityserver-discussions-components-files/14/7610.INA240A1_2D00_510k_2D00_IN_5F00_20KHz_5F00_2_2D00_5mohm.zip

  • In reply to BP101:

    Hi BP101,

    When simulation and reality don’t agree, I would look into setup differences. List the setup side by side and compare. An example - did you capture the input current to make sure it really is a linear 0.5 to 50A as you assumed in simulation?

    Regards, Guang

  • Guru 39180 points

    In reply to Guang Zhou:

    Guang Zhou
    did you capture the input current to make sure it really is a linear 0.5 to 50A as you assumed in simulation?

    I don't think you understand the 1st/2nd captures above post are not what Tina predicted for the very same HW configuration. The steady state current in CH2 first capture (8.2A) clamps to 0V when Tina model/s predict AIN0 does not clamp nor cross 0V. Same is true for Tina 50A plot, AIN0 never clamps to 0V.

    That seems to be no matter how -IN is configured in Tina model the output remains linear to the ±IN signal even when it crosses 0V. Goes to reason 240 is not level translating ±IN above ground as IG1 does in Tina transient analysis. Rather 240 incorrectly clamps -IN to ground, Tina 240 does not how can that be as we based all configurations on Tina model via IG1?

    So we need to see the 240 produce the current signal (1st/2nd CH2 captures) and not be clamped to 0V, rather rise above 0V as CMV magnitude increases. That is current measurement any ADC can easily extrapolate linear slope or ramp into steady state average.

    Like this plot (-IN=GND), (REF1,2=GND), 2mohm shunt, Note: ANI-0 is not clamped to 0V as Real 240 incorrectly does.

  • In reply to BP101:

    Hi BP101,

    Please attach your TINA circuit.

    Regards, Guang

  • Guru 39180 points
  • In reply to BP101:

    Hi BP101,

    You have the differential input set to 100mV in simulation, of course the output will be 2V.

    In case of PCB, is the current between 49A and 50A, as in simulation? Like I questioned previously, have you done the homework to make sure setups are identical between sim and reality?

    Regards, Guang

  • Guru 39180 points

    In reply to Guang Zhou:

    Guang Zhou
    You have the differential input set to 100mV in simulation, of course the output will be 2V

    IG1 is set to 50A and IC (initial condition) is 30mV  there is no shunt voltage other than what IG1 produced CMV across R11.

  • Guru 39180 points

    In reply to BP101:

    When we change IG1 to 10A or even 0.5A and the output AIN0-0 increased in a linear steady state as expected.