Sensor turn on time

We have had an issue with units automaticly waking from sleep when using code that switch off the Hall sensor when in sleep to save power. Today I took some time to investigate this instead of just using a workaround (not disabling the sensor while sleeping).

I had an idea that it might be that it takes some time for the sensor to output the correct value after getting power. This turned out to be correct but not in the way I expected. When the circuit is fed power at over about 3.1 V there is no delay for reading correct state of sensor. When the voltage drops to 3.1 V or under on the other hand it takes about 70 ms for it to output correct value.

In the below figures, C1 is the level at the Vs pin of the Hall sensor and C2 is at the output. Decreasing the voltage down all the way to 2.4 V (minimum working voltage for the sensor) there is no change in time to turn on.

Under threshold

Over threshold