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# AMC1311-Q1: ISO224 vs AMC1311 for measuring high DC voltage

Part Number: AMC1311-Q1
Other Parts Discussed in Thread: ISO224, AMC1311

Which one of the two isolation amplifiers are better to measure the output voltage (3.5kV) of a converter to regulate its output over a wide range?

Thank you.

• Hi Dumon,

The wider input range of the ISO224 will provide a signal to noise ratio benefit and higher accuracy measurement compared to the AMC1311. I recommend you take a look at our AMC Voltage Sensing Calculator: https://www.ti.com/lit/zip/sbar013

When looking at the ISO224, set the input voltage range to only be 6000 mV to model not using the negative half of the input range.

One other important aspect of designing for sensing such high voltage is the potential for failure. For example, the ISO224 has a rated working voltage of 2.1kV. In the event that the high-voltage divider resistors short out,  the ISO224 could potentially be subjected to 3.5kV between high and low-side grounds which degrades the expected lifetime of the device as shown in figure 4.

• Hi Alexander,

I could not understand the 6000 mV thing. Does +-12V not mean that the input signal swing between +12 and -12 around 0?

Thanks for sharing the link for AMC Voltage Sensing Calculator.

Another point is that if I use C2000 F28xxx MCU, I have to do gain adjustments in post processing amplifier that is actually used to convert differential output to single ended one with ISO224. But for AMC1311 the output is in the range of on chip ADC i.e. 0 to 3.3V.

As far isolation voltage is concerned I am going to take the risk on the fact that resistors are less vulnerable to short circuit on failure, since there is no such device available that can withstand Viorm greater than 3.5kV.

• If the IC gets damaged you might lose safety isolation. Don't play with your and others' lives

Kai

• Hi Duman,

Yes the input of the ISO224 swings +/-12V = FSR of 24V. However the calculator is only looking at the positive swing of the input range, not bipolar. So to model only using 0-12V, half of the available input range, set the input range to be 6000 mV.

From the calculation perspective, +/-6V is the same as 0-12V. Both are using half of the available input range.

Yes, this is true. A differential to single-ended conversion is not too difficult: www.ti.com/.../sbaa229.pdf