There are a couple of things to consider for the input fault and register update timing and sequencing.
First for the input fault, take a look at this section from the datasheet regarding input detection:
You may be running into issues on your input where something is occurring within the 200uS immunity timer to create a fault. You may want to check the waveform of your input to verify correct performance.
The next consideration is that it often take about 200-500ms to read/write for the device over I2C depending on the mode you are using (fast or standard). Keep in mind that this device can use I2C clock speeds of 100kbit/s up to 400kbit/s. The amount of time it takes to read and write will depend on the clock you are using but the process is shown below, where each period is determined by the falling edge:
It’s difficult to nail down exactly what may be going on with just that information, but you should monitor that input voltage to verify if there is a replicable fault condition.
Field Applications Engineer
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