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TMCS1100: TMCS1100A3 not working as expected when operated continuously for extended hours.

Prasanth Sahu
Prodigy 10 points
Part Number: TMCS1100

Hello, 

We are working on a project where were are using TMCS1100A3 current sensor to measure the motor current to control the motor. We want to run this motor continuously for extended hours. The motor runs for a few hours and stops. But there was current still flowing into the motor windings. On examining the current sensor signals, we found out that the sensor output is 0 V (should have some value when the current is still flowing through the windings), the supply voltage was still 5V and the reference voltage is 1.65 V reference (from a 3.3 V supply).. After we cycled the power to the circuit board, everything started to work properly again. 

Can I get help in understanding why we are facing this problem? The current sensor first works properly for a few hours continuously which lets the motor to spin, and then at some point of time, it would stop working (give 0V at the output) despite having the 5 V supply and 1.65 V reference (from a 3.3 V supply). However, we cycle the power to the circuit and it starts working again. We want the current sensor to work continuously for extended hours without any interruption.

Please find below the circuit schematic we are using for the current sensor:

Please let me know if you need more information.

Thanking you in anticipation.

Best Regards,

Prasanth

  • 0
    TI__Mastermind 27930 points

    Hello Prasanth,

    This does not make sense.  Are you able to isolate the TMCS1100 from the system?  Is the output getting loaded by something?  Have you verified the voltage at Vref pin 6 and Vout pin 7 directly on the TMCS1100.

  • 0 in reply to Javier Contreras4
    Prodigy 10 points

    Hi Javier,

    Thank you for responding. The TMCS1100 is being powered with 5 V supply and 3.3 V from the circuit shown below (5V_ISO is coming from an isolated power supply):

    I hope this answers your question about the sensor being isolated from the system.

    The output directly goes into one of the pins on the microcontroller.

    Also, we have measured the voltages at vref (6th pin) and vout (7th pin) directly on the TMCS1100.

    Please let me know if you see any issues here or if you need more information.

    Thank you.

    Best Regards,

    Prasanth

  • 0 in reply to Prasanth Sahu
    TI__Mastermind 27930 points

    Hello Prasanth,

    What I meant by isolation is removing the microcontroller connection to verify that the issue is the TMCS1100.  Have you restarted only the microcontroller?  Could there be another situation that could cause the part to Latch up? 

  • 0 in reply to Javier Contreras4
    Prodigy 10 points

    Hi Javier,

    We were working on repeating this failure, to implement restart only microcontroller. This time, the output voltage of the current sensor was 5V DC. Restarted only the microcontroller but the current sensor output didn't change.

    Thanks,

    Prasanth

  • 0 in reply to Prasanth Sahu
    TI__Mastermind 27930 points

    Prasanth,

    So the part latches up High and Low in two separate occasions.  Is there any information you can give me about what happens before this happens.  I can try to reproduce but I would need to know the conditions to reproduce.

    Please share any information you can about the schematic connections to microcontroller or any other connections and part number if possible.

  • 0 in reply to Javier Contreras4
    Prodigy 10 points

    Javier,

    We don't know what happens before this happens, but the circuit and motor runs normal for a few hours and then the motor stops. So it is challenging to observe what happens before this.  

    I am putting the schematic of current sensor and microcontroller connections here:

     

    The microcontroller part number is: EFM8BB10F8G-A-QSOP-24R

    Please let me know if I am missing something. Also, if there is something I should do to provide you information, please let me know.

    Thanks,

    Prasanth

  • 0 in reply to Prasanth Sahu
    TI__Mastermind 27930 points

    Hello Prasanth,

    I just realized Vout of the TMCS1100 can go upto 5V while the input of the microcontroller is limited to 3.3V.  You could have a condition where the output voltage of the TMCS1100 is too high.  I think the A3 version can be powered with 3.3V to limit the output.  Could this be the issue?