I am working on a battery-powered application. Since power saving is a must, this design using high-side power node controllers (part number MIC94042) to power-on or power-off specific voltage nodes that power specific peripherals.
These peripherals are all controlled by pins that come from an external GPIO controller. The only exception to this is the external GPIO controller, which is also connected to its own power node that can be controlled by either setting or resetting P0.26 on the nR52 (the logic is direct and not inversed so a High means enabled and a low means disabled). The external GPIO controller is the has the only power node that is directly controlled by the MCU; ever other power node is controlled through the SPI-based external GPIO controller (part number MCP23S17).
Here is the problem. When power is killed on any of the power nodes tied to the external GPIO controller, everything works as expected. However, when power is killed to the external GPIO's power node, the nRF52 resets. After looking at the RESETREAS register, I see the that soft reset bit is set. I have been looking with a scope at both the power line of the MCU and the nReset line of the MCU and cannot see any glitches that could cause a problem (I am AC coupled and looking for spikes around 200mV and at around 100 - 500 milliseconds).
I believe that something with the power is causing this reset, but I am not able to see it. Can someone help me identify what is going on? Also, the internal DC-to-DC regulator is enabled, but this does not seem to make any difference.
Thank you!
