Timer capture is a method to read the DC fault by reading duty cycle shifts from the auto-oscillation circuit. This is a common measurement technique in RCD modules. With a DC fault condition, the duty cycle of the DRV8220 shifts as the B-H curve or magnetization curve loop shifts. The DC fault current through the core causes saturation slightly quicker in one direction than the other. This translates into a measurable shift in duty cycle.

This approach was sensitive to noise in components, oscillators, and magnetic cores. This approach is found to require more expensive components with less delay, and faster MCU clock speeds. There was a large inconsistency of duty cycle shift dependent on which magnetic core was used. In many cases, the jitter caused by noise blinded the signal, causing false trips.

Reading a DC fault with an ADC on the output of the filter path resulted in a lower cost BoM and more accurate readings over a broader selection of fluxgate sensor material types.