Mity CPU Platforms » MitySOM-QC6490

The only "automatic" power on we have implemented so far is software control from an Arduino.

There are two main stipulations on the POW-BTNn:

1. The power on pulse must be greater than 400ms.
2. A power button press of 10s is a system reset.

Automatic power on can be accomplished with a programable timer.

For example, I did a quick search and I came across the TPL5111DDCR (See section 7.4.3 of the datasheet). In this case you would need the output of the TPL5111DDCR to drive the gate of an N channel MOSFET, the source tied to GND and the drain tied to POW-BTNn. POW-BTNn is pulled up to 1V on the SOM so this implements the open-drain inversion of the TPL5111DDCR output accomplishing the automatic pulse on the POW-BTNn signal on power on.

Please let me know if there are any further questions!

Thanks!

Does power have to be high for a certain amount of time before the power-on pulse? If so, which rail and for how long?

Or can POW_BTNn be held low at startup, and released after 400ms?

When talking about input power to the SOM that would be the 3V7-BAT rail.

There would be a delay between power being applied (on 3V7-BAT) and when the SOM would be monitoring the POW-BTNn but we haven't quantified this yet. We will set a test up to figure out the minimum delay time and update this forum as well as the datasheet.

The POW-BTNn can be held low at startup to trigger the power on sequence of the SOM. The slight problem with this is that instead of just the 400ms minimum "pulse", there is the additional time added from when power is applied to when the "pulse" is monitored in addition to the 400ms.
I did a crude test with the development kit and holding the POW-BTNn low for ~1 second after power is applied was enough to trigger the power on sequence. We will also quantify this and update the forum and datasheet with more exact numbers.