RE: Exercise Azure Sphere Low Power Features

bwilless — Mon, 15 Jun 2020 20:36:58 GMT

[mention:b044d5482b544ac9966ff7da42217000:e9ed411860ed4f2ba0265705b8793d05] had a great idea for an improvement, so I thought I would capture it here.

Rather than have the user wait 120 seconds for the MT3620 to go into POWERDOWN, why not just have the user press button-A (or button-B) on the SK board when they are ready to put the device in POWERDOWN mode?

RE: Exercise Azure Sphere Low Power Features

peterfenn — Mon, 15 Jun 2020 20:20:07 GMT

This Starter Kit’s hardware implementation for support of POWERDOWN, was designed prior to the release of support for this low power mode.

The MT3620 POWERDOWN mode can be correctly entered, then later exited via expired timer or WAKEUP signal events, but the overall implementation on this board has some shortcomings:

EXT_PMU_EN: The state of this output does not disable the main 5V to 3.3V dc/dc regulator

Consequently some devices external to the MT3620 Sphere device remain powered and drawing current from the 3.3V rail (eg. the FTDI USB-Serial bridge device)

WAKEUP: The pullup resistor for this signal is tied to the 3V3 rail instead of the 3V3_RTC rail (this pullup is on the Sphere module, not the Starter Kit)