[G400]GPIO behavior when the SOM is not power supplied

I am observing something on my custom g400 based board.

I am using a press button connected on PD4. This button is also connected to powerpath controller that switch on/off 3.3VDC supply after a dozen of second.

The IO is externally pulled high using a 47k resistor connected on a+5V permanent power supply (I know G400 IOs are only 3.3V compliant but I had forgot and I designed the system like that). A debouncing capacitor of 0.1µF is inserted between the io and the ground.

When I switch on the system, all is perfect. Problem occurs when I press button. The powerpath controller switch of the 3.3V and the G400 is therefore at OFF state. I was expecting to be abble to swicth on the device again using the button but this does not work. In fact I still have the 5V but IO is now at 900mv which seems to indicated that current is consumed by the IO even if the processor is switched off.

Can anyone explain this?

I am not sure I have an answer but the first thing you need to do is remove that pull up resistor off your board and then add one to 3.3V, or use the built in if that is enough.

Hi Gus

Problem solved. The power path controller was not properly soldered… :wall:

This is not solved anymore, I removed the Pullup on 5V, the LTC2952 powerpath controller has an internal pull up resistor. Unfortunately the PD4 pin consumes too much current when it is not power supplied. Is there something I could miss?

How to know at an early stage of design, that some IOs will draw power while the SoM is not power supplied?

@ leforban - We are looking into this issue.

@ Aron, thanks for your interest in this issue. Please let me know if I can do something to ease in solving this.

Hi Aron, any news about this? Is it something expected? How to avoid that?

@ leforban - We are still looking into this issue. We will try to provide an answer as soon as possible.

@ leforban - As I was looking into this, I must not have been fully understanding what the situation is. Regarding the PowerPath Controller, what are you using it for? Is it to control the power for the G400? Can you re explain the situation to where I can better understand it?

Hello Aron, yes the power path controller LTC2952 manages the power supply of the G400D , it controls an 3.3V LDO that is directly connected to VCC pins of the SoM. The power button is shared between PD4 pin of the SoM and the PB input of the LTC2952. The PB input is pulled up by the LTC2952 and I was expecting to have at least 3V but the G400D seems to draw all the current on PD4 ( removing the SoM proves that the PB input works as expected but as soon as the SoM is placed the voltage is near 300-500mV which is below the threshold of PB input and I can’t obtain the falling edge to restart the board.

Hello Aron I have a batch of 10 PCB that is waiting somewhere in germany for being populated with components… Is there a way to have a fast answer? May I call you directly?

Aaron is not in today but I was reading this thread and I also do not understand what are you trying to do. Maybe a little drawing diagram?

I would like to switch off/on the device using bp_pow button, It works great to swicth off but I can’t switch on the G400, it draws all the power sink by the LTC2952.

can I call you (or someone else) today or tomorrow directly? if yes how to do that? I call GHI directly?

Of course, if I am not around then talk to Gary please.

Have you considered a diode in the line from the G400? That would block the high from the G400 but allow the LOW state to activate the device.

Hello Dave unfortunately, it will not work, I also need to detect a low level on the SoM when the device is alive…

Hi Aron sorry phone communication has been lost… :-[

I will run the following experiment Connect just the ground of G400D and apply a voltage about 3 V on PD4 and will let U know.

Ok experiment has been done,

Gnd connected on G400HDR board, apply 3.3V on PD4 starts the board !!!
The pwr led of G400HDR lits, the PD3 led is still off but 100mA is consumed by PD4!