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TIDA-00555: Regarding voltage sensing and current sensing calculations

Part Number: TIDA-00555
Other Parts Discussed in Thread: TIDA-01606

Dear TI team,

Good morning.

In voltage sensing calculation in Tida-00555,below calculations are considered.

Voltage to be sensed=230V

Add 20% to 230V That is 276(As per Tida-00555)

1. why 20% is being added?

Then 276VRms value converted to Vp-p value by multiplying 1.414

That is (276*1.414)=390V(As per TIDA-00555)

2. Why  we need to convert RMS value to peak to peak value?

3.Do we need fallow above procedure for shunt type current sensing also?

A. Is above theoretical calculations applies for practical calculations also?

B. How good above calculations are when comparing with practical results?

C.Kindly share results document comparing theoretical and practical values if TI team having (Tida-01606 or any other reference design involving voltage sensing and current sensing)?

3.Do we need to convert IRMS to Ip-p in current sensing application calculations?

We need above details to accurately calculate and simulate in AC voltage and current sensing (Shunt )applications.

Kindly do the needful.

Thank you,

Girish Kantharaju

  • Hello Girish,

    Thanks for reaching out.

    1. There are 20% of margin added, since the grid voltage will not be exactly 230V, but can vary by a few %. Adding 20% is more on the save side, but we recommend to add some margin. Depending  on your environment 10% of margin might be suficient.
    2. You need to look at the Peak to peak value, because this will be the maximum voltage which is applied to the circuit. The actual waveform is measured and then RMS values are calculated.
    3. Yes also for a shunt base implementation there should be some margin added and the peak to peak value needs to be considered. The circuit in TIDA-01606 is a different, since there an isolated amplifier is used for current sensing and a non differential amplifier is used for voltage sensing. Also for current sensing you have to consider the Peak to peak values. 

    Obviously, the results in practice will depend on the components you are using. Important factors are the resistor tolerances, gain and offset errors of the amplifiers and resolution of the ADC.
    Practical Performance of TIDA-00555 can be found in the design guide from page 31 on.

    I hope this helps.

    Best regards,

    Andreas