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INA225-Q1: Pwm signal management current sense

Prodigy 80 points

Replies: 13

Views: 268

Part Number: INA225-Q1

Hello

I am using the Ina 225 but I think that I do not know to use it with a PWM signal. As a Pwm signal the value is in the modulation and not the peak. So, i am use that I lack some knowledge.

So, please tell me, who reads this bottle in the sea, how do you manage a pwm signal with a INA225.

Thanks to all for your help

Regards

Vincent

  • Hello Vincent,

    Most amplifiers do not do well with PWM signals an the inputs as the Common Mode of the inputs vary so much and the AC CMRR are typically very low as the frequency increases.  Since the PWM has the large slew rate it includes very high frequency CM changes causing issues with some amplifiers.  Also you need the amplifier to be fast enough to recover from the CM rapid change before the signal changes.

    I would recommend looking into the INA240-Q1 which has some PWM rejection circuitry.  Two plots to consider looking at is the Common-Mode Rejection Ratio vs Frequency and Gain vs Frequency.

    Best Regards,

    Javier Contreras, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

     

  • In reply to Javier Contreras4:

    Hello Javier

    Thanks for your message. Some people told me to check a RC filter at entrance in the way to convert PWM into a DC voltage, I will do that this afternoon. What I don't undersand is why those products as INA1225 are recommended in datasheets to go with PWM circuitry. That I don't understand. 
    Regards and thanks 

    Vincent

  • In reply to Vincent HURET:

    Hello Vincent, 

    Be careful when using and input filter and please look at section 7.4.1 of the datasheet.and the gain error as you place a large resistor at the input.

    I understand why someone would recommend this device for the PWM application as this is one of our higher speed Current Sense Amplifiers.  I think I missed that section on the data sheet.  Can you point me to what section you are referring to?

    Best Regards,

    Javier Contreras, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

     

  • In reply to Javier Contreras4:

    Hello Javier

    I have solved my problem with a RC filter just before going to the, not the INA225 but I have changed to INA128 because of the package DIP;

    it works well IF i let IN+ FLOATING and if I enter the RC treated signal on IN-. Unbeleivable but it is like that

    If you have some explanation, welcomed. Next time, I will be a lawer than engineer, I have often the feeling to have an IQ of 43 ..smile

    Have a nice day, 

    Vincent

  • In reply to Vincent HURET:

    Vincent,

    I am glad you solved your issue.  Please let us know if you have any further issues.

    If you would like more explanation I would like to see a schematic to make sure I completely understand.

    Best Regards,

    Javier Contreras, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

     

  • In reply to Javier Contreras4:

    Hello Javier

    I hope that you are going well.

    I have a bad news. As you know, I have a currens sens resistor that gives 35 mV at 100 A and I am working at 100A. The signal is a PWM one at 1KHz 14 V or 28 V depending if it is a car or a truck ( automotive )

    I have made the same circuit with INA128, INA 225 and 301 but I have decided to go on the AD627. For unknow reason, and it is the same circuit ( I have a IC holder where  I replace the IC with switches ), the TI items doesn't react at all when I increase the current value.

    AD617 disadvantage is the voltage range, but maybe I will find a solution .

    If you have any understanding why TI units doesn't react, tell me, it is really strange. And the curcuit is direct,..means really simple. I place the AD627, works, I put in place any TI...nothing moves when I moves..And the gain resistor or inputs are ok as well.

    Add, I have to manage something with SG3524, but I beleive that it is not a sense subject. Otherwise, tell me.

    Regards and have a nive week end

    Vincent

  • In reply to Vincent HURET:

    Vincent,

    I would still guide you to the INA240 with the PWM rejection. This device is meant to deal with the rapid CM changes with PWM signals.

    Best Regards,

    Javier Contreras, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

     

  • In reply to Vincent HURET:

    Vincent HURET
    it works well IF i let IN+ FLOATING and if I enter the RC treated signal on IN-. Unbeleivable but it is like that

    Pardon - but is leaving so critical an input pin 'Floating'  (now/here) deemed 'Accepted Practice?'    Hopefully this user statement has 'escaped vendor notice' - and the practice (key input allowed to Float) is NOT recommended!

  • In reply to cb1_mobile:

    CB1,

    I did miss the input floating.  I may have seen the solved issue and moved on.

    Vincent,

    Please send me a schematic so I can better assist.  Also I still recommend the INA240.  Also please detail the input function you are using.

    Best Regards,

    Javier Contreras, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

     

  • In reply to Javier Contreras4:

    Hello Javier and thanks

    I will listen to you and try to find an INA 240 to check. 

    To be honnest, I get the best results with an AD627 but the voltage range is too short for me. Nevertheless, it gives a good example about specifications that I need. Regarding the schematic, it is very simple design. 

    The shunt is 75 mV for 200 A, and I need to regulate at 50 A and 100A

    The pwm frequency is 1 KHz, not so much but until now the INA 225 and 301 are "blind"...

    Thanks for your help Javier, and I will isten to you regarding the INA 240

     e.