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UC1625-SP: Using an OpAmp to Drive inputs into ISENSE 1 and ISENSE 2

Elias Tarver
Prodigy 50 points
Part Number: UC1625-SP

I want to have the overcurrent shut down set to a very small current without having the actual current sense resistors themselves go up drastically in size to accommodate it.  Is it possible to drive these signals with an additional OpAmp for additional gain adjustment?

  • 0
    TI__Mastermind 18976 points

    Hi Elias, 

    I'll get back to you on this question by the end of the week 

    Best Regards, 
    Andrew 

  • 0
    TI__Mastermind 18976 points

    Hi Elias, 

    Just a follow-up here, I am still looking into this question but will aim to give you a response within 2-3 days 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    TI__Mastermind 18976 points

    Hi Elias, 

    Thanks for your patience.

    Interpreting your request and problem statement, the main obstacle is that the integrated CSA for overcurrent protection has a fixed gain setting of approx G=2V/V. 

    If what you seek is to achieve a different current-sensing "range" (e.g. something that can be achieved with a higher Gain value or a different shunt resistor), It may be best to configure the PCB circuit to effectively disable this chip's integrated CSA overcurrent protection and instead use an external OpAmp like suggested. 

    I am not exactly sure what the correct procedure would be to do so for this device, as it was released over 10 years ago. However, what we generally do on our newer devices is short the CSA inputs together and tie them to GND (such that CSA input = 0V) and float the CSA output if applicable. That way, the integrated CSA's output reflects no overcurrent (or any current, for that matter) in the overall system. Hope this helps 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    Prodigy 50 points

    How do I find out what someone should do with this device vs an example of something else?

  • 0 in reply to Elias Tarver
    TI__Genius 13550 points

    Hi Elias,

    Andrew is currently out of office for the next few days but will aim to provide a response early next week.

    Best,

    ~Alicia

  • 0 in reply to Alicia Rosenberger
    Prodigy 50 points

    I wanted to check in on the progress of this item.

  • 0 in reply to Elias Tarver
    TI__Mastermind 18976 points

    Hi Elias, 

    My apologies for the delay in response here - our team has been experiencing a high volume of support requests.

    To give a response to your latest question: 

    Elias Tarver said:
    How do I find out what someone should do with this device vs an example of something else?

    A: the description I provided earlier should be a generic best-practice applied to most gate driver devices, including this one. For UC1625 specifically, there is a comment in the ISENSE/ISENSE1/ISENSE2 pin descriptions that note how the overcurrent threshold is set. Because the gain on this device is set to ~2V/V, there is no choice (when using this CSA) to update the UC device's OCP trip threshold without modifying the shunt resistance. 

    However, if you want to instead use an external CSA and/or external MCU to intervene based on calculated motor phase current (by monitoring E/A OUT and ISENSE output values), then this fault response needs to be handled externally with the MCU's software. We would be effectively be offloading the OCP response to the MCU, and selecting an Rsense value such that the OCP thresholds (0.2V/Rsense or 0.3V/Rsense) are never achieved. 

    As this device is 12+ years old and our team does not have local hardware or simulation databases to evaluate further, this would need to be validated in your system directly by testing on the application PCB - we would advise selecting a newer device from our DRV8x portfolio to ease the design process. 

    ISENSE CSA description, including overcurrent comparator: 

    E/A Error Amplifier description: 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    Prodigy 50 points

    Is there anything in the DRV8x portfolio that is rad hard and available in grade 1 or grade 2?  I haven't been able to find any of those available from your website.  If not, then they are not a viable replacement for use of this device.

  • 0 in reply to Elias Tarver
    TI__Mastermind 18976 points

    Hi Elias, 

    Today, no - we don't have other rad-hardened products in our DRV8x portfolio. 

    You may need to consult the power management forum for isolator/non-isolated gate drivers that may meet this requirement. 

    Best Regards, 
    Andrew