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Original question:

TMCS1101: Current measuement resolution

TMCS1101: Current sensor with better than 50uA resolution

Hung Ching Hsu
Expert 3086 points
Part Number: TMCS1101
Other Parts Discussed in Thread: TMCS1100,

Hi Team, 

My customer is asking if TI have current sensor that fits following requirement, could you kindly help?

Voltage rating : around 500V dc

Resolution : better than 50uA

Regarding voltage rating, TMCS1100 and TMCS1101 supports 600V working voltage so 500Vdc should be okay for TMCS1100 and TMCS1101, right?

And from this thread, I think resolution depends on the bit of ADC and Ax variant of TMCS1100 and TMCS1101 customer uses. 

If customer uses 20 bit ADC with 5V and A4 variant(400mV/A sensitivity) of TMCS1100 and TMCS1101, customer can fulfill 50uA resolution, is it correct? 

If so, I will recommend TMCS1100 and TMCS1101 to customer. 

Thanks.

Regards,

Jo

  • 0
    TI__Mastermind 22385 points

    Hung, 

    The actual resolution that would be possible here for a 20bit ADC with a 5V reference, the LSB is 5/2^20 = 4.78uV per code. 

    We can then use this along with the sensitivity of the device to refer this back to the input current

    For the A1 device, the sensitivity is 50mV/A, and therefore the resolution works out to 95.4uA/code

    A2 is 47.7uA/code

    A3 is 23.8uA/code

    A4 is 11.9uA/code

    As you can see, an increase in the "gain" (sensitivity) of the device leads to an increase in the resolution of the system, so the answer to your question is yes, the A4 variant should work here. The A2 variants and above will provide the customer the resolution they need here, but this comes at the tradeoff of dynamic range, as shown in table 5-1 of the datasheet. The A1 variant is about half the resolution they desire here. 

    Alternatively, if the customer needs the A1 variant, they could improve the resolution by moving to a larger ADC, such as a 24bit.