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Original question:

WEBENCH® Tools/INA193: Eload Compensation

WEBENCH® Tools/INA193: Electronic load design.

Vishal Kakade
Expert 1625 points
Part Number: INA193
Other Parts Discussed in Thread: OPA192

Tool/software: WEBENCH® Design Tools

Hello,

This post is referenced to the below link. Since there was no response, I am making a new post.

https://e2e.ti.com/support/amplifiers/f/14/t/826135?tisearch=e2e-sitesearch&keymatch=%20user%3A412098

I will explain the complete problem statement. Please tell me different ways to achieve it.

Q. I wanna design an ELoad Circuit where-in, I should be able to set the current from 0A to 5A.(It should reach the set current within 15 to 20uS).

The requirement is, there should not be any overshoot nor any Oscillations. We had different approaches like Setting current to 4.5A and then slowly increase it to 5A by reading current and adjusting the DAC voltage. But due to Response time mismatch, and delay in a feedback loop it is not possible.

Can we design a compensation circuit similar to one in the Buck Converters wherein it compares feedback voltage and adjusts the PWM automatically, So instead of voltage, we should be able to do it for current in our application? Or can it be achieved by using same opamps for Mosfet gate drive and current sense with higher slew rate and lower input offset voltage?

Regards

Vishal Kakade

  • 0
    TI__Mastermind 32260 points

    Vishal,

    Let me work on this and I will get back to you tomorrow.

  • 0 in reply to Javier Contreras4
    TI__Mastermind 32260 points

    Vishal,

    Sorry for the delay.  I did get the circuit you posted stable but it did require a large capacitance and was not very robust as you would change any part of the circuit and it would become unstable.

    Is there anyway you can use a slower amplifier?  The loop is limited by the INA193 speed and will be limited by that.  The higher speed amplifier is the reason the compensation is so difficult.

    On the Buck converter technique I am not an expert on that and would not be. 

  • 0 in reply to Javier Contreras4
    Intellectual 930 points

    Hello Javier,

    Thanks for your response, I can't use a slower op-amp since I need faster rise time, So instead I replaced the INA193 by and Same Op-Amp which is there in the Gate driver. With this, I am able to get good response.

    I just wanna know what compensation circuitry is needed?

    Regards

    Vishal Kakade

  • 0 in reply to Vishal Kakade
    TI__Mastermind 27715 points

    Hi Vishal,

    I've asked the engineers in the precision amplifiers team who are expert in the OPA192 to assist with this question.

    Best regards,

    Ian Williams
    Applications Manager
    Current Sensing

  • 0 in reply to Ian Williams
    Expert 1625 points

    Hello Ian,

    For MOSFET to turn on faster, is there an analog MOSFET gate driver? Currently, I am driving the gate of the MOSFET with opamp which has a limited output current. Is any way to boost this current without affecting the output voltage? So that my turn-on time increases.

    Regards

  • 0 in reply to Vishal Kakade
    TI__Guru* 93105 points

    Hello Vishal,

    We do not produce any specific product referred to as a MOSFET gate driver here in Precision Amplifiers.

    You mention you are driving the gate of a MOSFET. Which Op amp is driving the MOSFET, U12 or U13? What are the MOSFET characteristics i.e. part number, gate capacitance, threshold voltage? The OPA192 can drive about 50 mA so it does have fairly hefty output current drive capability. Most of our Precision Amplifiers Op amps have a maximum output current less than that level. And for your application is sounds like it needs momentarily high output current that can change quickly. That implies a fast slew rate as well. The OPA192 may not be able to deliver the speed/current fast enough to drive the MOSFET in the 15 to 20 us timeframe required.

    TI's High Speed Amplifier product line offers a number of high-speed Op amps that have very wide bandwidth, very high slew rate and high output current capability. You may find that one of their Op amps provides you the performance your application requires. You can obtain more information about the High-speed Amplifiers here:

    http://www.ti.com/amplifier-circuit/op-amps/high-speed/products.html

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Genius 10850 points

    Hi Vishal,

    We haven't heard from you in a while, we hope we were able to resolve your issue. I am going to close this thread now. Feel free to reply to this thread if you have any questions moving forward with this design.

    -Tamara