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TMCS1126: demo board output 20mV noise when there is no input

Gary Zeng
Intellectual 1145 points
Part Number: TMCS1126

Tool/software:

Hi experts,

Customer is using TMCS1126A1 on their own board. A1 is 20mV/A. They found that output has a 20mV noise when there is no input, both on their own board and TI demo board.

Do you have some suggestion to remove the noise?

  • 0
    TI__Mastermind 32260 points

    Gary,

    If the customer does not need the full bandwidth then you will need to filter.

    https://www.ti.com/video/4078827152001

    Assume 1/f noise =not an impact

    A1 = 25mV/A

    Noise density: 150µA/√Hz

    Bandwidth: 550kHz

    Assume single pole at output: 1.57

    RMS noise = 1.57*150µA*√550000Hz = 175mA

    RMS noise in output voltage = 175mA/25mA/V = ~7mV 

    Peak to Peak = RMS *6  = 42mV

    Regards,

    Javier

  • 0 in reply to Javier Contreras4
    Prodigy 10 points

    Javier,

    That is more of an excuse than an answer.
    I too, see this noise in my application in all the TMCS sensors.
    The problem is that the noise is random and "LOW" frequency.
    To filter it would make the sensor useless for control and it's response time irrelevant.
    Pretty sketchy marketing here.

    Steve

  • 0 in reply to Steven Geissler
    TI__Mastermind 32260 points

    Hello Steve,

    What is the issue you are seeing exactly for low frequency.  From the question above I had no context of low frequency noise.  Is your issue with the TMCS110x family.  As we have an explanation of that in this application note:  An image below from that application note.

    Can you share what device you are using and a screen shot of the low frequency noise?  Also if you have a definition of low frequency.

    Regards,

    Javier

  • 0 in reply to Javier Contreras4
    TI__Mastermind 32260 points

    Gary,

    Here is a correction on expected noise.  I placed the 1.57 outside the Sqrt.  I highlighted the updated values.

    Assume 1/f noise =not an impact

    A1 = 25mV/A

    Noise density: 150µA/√Hz

    Bandwidth: 550kHz

    Assume single pole at output: 1.57

    RMS noise = 150µA*√(1.57*550000Hz) = 139mA

    RMS noise in output voltage = 139mA/25mA/V = ~3.5mV 

    Peak to Peak = RMS *6  = 21mV

    Regards,

    Javier