When measuring supply currents in the single digit microamperes (uA), it is important to inspect the board schematic for external loads including pull up resistors. For example, if using the MAX32660-EVSYS, it is important to note that the DS28E05R+T is also being powered by the HDR_VIO net if R9 is populated. In order to establish a base measurement, it is best if nothing is connected externally to the GPIOs and they should be configured as inputs with the internal pull-ups or pull-downs enabled. Additional conditions are: RTC enabled and 96kB SRAM retained.
In summary:
- RTC enabled
- All GPIOs set to input with the pull-up enabled (pull-down yields similar results)
- Nothing connected to the GPIOs externally
- 96KB SRAM retained
If the GPIOs are set to Hi-Z, the current jumps to a higher value, so it is important to make sure the GPIOs are in a steady state.