I am developing a custom carrier board for IMX8M Plus and I am a bit confused about power button.
I am planning to use the same push button controller (LTC2954CTS8-2#PBF) as Verdin Development Board V1.1.
In the design, LTC2954CTS8-2#PBF INT# pin connected to CTRL_PWR_BTN_MICO#. But INT# is not asserted at the fist push to start system. Only asserting the EN out to enable the DC-DC converter.
So, I understand that when I long push to button to start device, EN pin of button controller enables the DC-DC converter and module is powered. In this moment, module will start no need anything but power.
When I long push to button to off the device EN pin deasserted and INT pin of button controller asserted last time according to the datasheet. So, EN pin disable the DC-DC converter and module will be off.
There is no problem so far.
But what if I push button shortly during the module “Running” state?
Button controller INT# pin will send interrupt to CTRL_PWR_BTN_MICO# and this will cause to module off.
Could you please guide me for this matter?
Hello @oguzhan.caliskan ,
I assume that you are looking at this data sheet:
This is the failsafe use case, as described in section Adjustable Power-Down Timer (page 9 of the LTC2954 data sheet) . It would be used when the SoM does not respond to any input.
In this case the DC-DC converter will be disabled regardless of the SoM having finished the power-down sequence, since the LTC2954 doesn’t look at the KILL# input signal. (see the time diagram below)
This would be the “normal” behavior.(Turn off section in page 9 of the LTC2954 data sheet) A short push triggers the interrupt, the SoM powers off “nicely” , then it asserts the KILL# signal via CTRL_FORCE_OFF_MOCI# and the DC-DC converter is powered down.
Is there any special reason why you want to distinguish between a long power button press and a short one?
Hi @josep.tx ,
Thank you for fast response.
Actually, our scenario was like;
First long push - Turn on,
Multiple short push - Start to do something functional in software,
Last long push - Turn off.
But I guess in our scenario, turning off with a long push is not a safe action to turn off the device. Right?
So, I can change the scenario like;
First long push - Turn on,
Short push - Turn off the device and DC-DC converter via CTRL_FORCE_OFF_MOCI# through LTC2954.
Last log push - Turn off the device immediately if it’s not responding or etc.
But this time, It seems I am loosing the short push interrupt actions because it’s using for power down.
yes, you described it the right way. if you had a carrier design without the external push button controller, the module would start with just applying power to it. The SOMs CTRL_PWR_BTN_MICO# pins functionality is described here.
Now some could argue that the CTRL_PWR_BTN_MICO# has kind of the same functionality as the external push button controler. But what if the SOM module is shut down via software? What would happen to the Dc/Dc converter on the carrierboard? It would be still on right? So that short INT# pluse to the CTRL_PWR_BTN_MICO# pin triggers a special shutdown mode. This will shut down the module software but at the end of that shutdown process, it will trigger the CTRL_FORCE_OFF# pin. This pin will then kill the external power to the SOM with the help of the LTC push-button controller. That kills the enable signal to the DC converters when the SOM triggers the CTRL_FORCE_OFF#. So that there is no power consumption of the DC DC converters if the SOM is off.
Please read the carrier design guide chapter power management starting on page 73. https://docs.toradex.com/108140-verdin-carrier-board-design-guide.pdf
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