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TMCS1100: CMRR and Peak current Rating

Brian Wang0928
Genius 13190 points
Part Number: TMCS1100
Other Parts Discussed in Thread: INA240

There are some questions about the Hall-based and Shunt-based current sensor. Customer is now using INA240, but he is also interested in TMCS1100. 

1. Regarding to the CMRR performance in the current sensing, the unit for the shunt-based as INA240 using the dB value, but in the TMCS1100, the unit is by uA/V. and it seems it's not relative to frequency? How to compare both units? Could you offer an example! 

2. Regarding to the below table, what is the current unit, it is RMS value? How about the peak current max. rating?

  • 0
    TI__Mastermind 31600 points

    Hi,

    We’ll get back to you with any suggestions next week.

    Regards, Guang

  • 0 in reply to Guang Zhou
    TI__Mastermind 24985 points

    Hello Brian,

    Thanks for reaching out on the forum.

    1. I do not have a CMRR vs. frequency plot to provide yet.  However, I can provide some insight on calculating for DC and low frequency Vcm signal cases.

    The key take-away here is you can actually improve the CMRR error for the shunt based device.  While with the Hall based device the error cannot be improved.  This is because your customers Iin is constrained by the system and likely cannot be conveniently adjusted for for the sake of better CMRR error. On that note, be sure to use the Iin minimum as that will provide the worst case error.

    2. Those values are apply DC signals as well as AC signals with an RMS equivalent to that DC signal.  If you want peak signal measured within the linear range, you can use the last equation in column two of the table above.  If you want the peak current the device will survive, then it hinges upon the duration the device sees that peak current.  To determine that, your customer should calculate the RMS value for their expected load and see if falls under the curve in figure 10.  Alternatively if they have one large peak transient they can use figure 11 in the datasheet.