Zero-voltage Cross Detection

Zero-voltage Cross Detection

Safety Features Technique

This technique can be used in GreenPAKs that include ACMP’s.

Zero-voltage cross detection is commonly used as an accurate method of detecting AC characteristics, such as frequency and phase.

GreenPAKs have a pin voltage range of 0V to a VDD value of 5.5V. To interpret an AC signal that crosses at the 0V point using the GreenPAK a DC offset shift should be implemented between the AC signal and the GreenPAK pin. This can be accomplished by a 1:1 resistor divider between VDD of the GreenPAK and the AC signal, shown in Figure 16.

Figure 16 Basic DC Offset

Zero-voltage cross detection requires, at minimum, one or two comparators and a counter. The comparators check the incoming AC signal against a reference voltage, which can either come from the GreenPAK’s available reference voltages or an external reference point. If a desired ZVCD voltage is greater than the available GreenPAK reference voltages the AC signal may instead be reduced by using the IN+ gain option within the comparator’s property settings and comparing the reduced AC value to a similarly-scaled reference (Figure 17).

Figure 17 Using the IN+ Gain to Measure a 1.7V Crossing

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