TIDA-01639 results
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In this video within the implementing isolated shunt sensors using isolated delta sigma modulators and digital filters section of the training series, we will cover the process used to test the results of the TIDA-01639 reference design, as well as the results obtained with this reference design.
To test both the isolated modulator, and isolated metrology AFE designs, we use a source generator slash reference meter, which is integrated into our test equipment shown on the left. For the test performed, the source generator provides voltage and current waveforms that are fed into our reference designs. Based on voltage and current applied to the meter, the meter would output pulses that are proportional to the amount of energy consumption. These pulses are then fed back into the equipment, which uses its reference meter to determine, what is the percentage error of the meter? These pulses are used to calibrate the energy measurements of the meter, along with test the energy accuracy of the meter itself.
For calibrating our designs we perform, gain calibration of voltage and current, gain calibration on active power, power offset calibration, and phase compensation. Phase compensation is necessary to ensure that the voltage and current samples are synchronized, so that any phase shifts from voltage and current are due to load conditions provided to the meter instead of the actual meter front-end circuitry.
For the tests conducted, we used a nominal voltage of 230 volts, a calibration current of 10 amps, and a frequency of 50 hertz. The meter was set to output 6,400 pulses per each kilowatt hour of energy. In our test, we used both 400 micron and 220 micron shunts. Here we see the active energy error results of the TIDA-01639 when using the 400 micron shunts. For these results, we compared current and voltage-to-current phase shift.
At high currents, the shunts get hot, which causes the resistance to drift, thereby causing a similar drift in the active energy error. However, despite this trend, all the results were still within 0.5%. We performed the same test using 220 micron shunts instead of 400 microns. From these results, you can see that the results are still within 0.5%.
Another test that we performed was a frequency variation test. In this test, we varied the mains frequency by 4%, and did not see the energy error vary by more than 0.03% from the results at 50 hertz. A voltage variation test was also performed. In this test, the active energy error is measured across a voltage range from 80 volts to 270 volts. The error resulting from the test was less than 0.02% across the voltage range.
This test is important for two reasons. First, it shows that the 14-bit SAR ADC used to measure mains voltage has sufficient accuracy. Second, it shows the voltage range at which the AMC1106 would operate, which is more important for this design than the TIDA-00601 design, because the high side of each AMC1106 in this design is powered from mains using the cap-drop supply.
For the test, we found that 80 volts was the minimum voltage that the AMC1106 was able to be powered from using our cap-drop power supply. We verified this by looking at the metrology energy percentage error from our reference meter.