Teensy 4.1 Not Resuming from ON_OFF_SW suspend.

[waterlubber]

I've got a Teensy 4.1 on a custom board that's having issues with the VBAT / 3.3V regulator suspend. There's a feature where, when VBAT is connected, the Teensy will "remember" its power state when 5V is removed; pulling ON_OFF_SW on the Teensy to ground for 4 seconds will put it into a suspend state where it disables the on-board 3.3V regulator; pulling it to ground for 0.5 s *should* resume it from suspend, but it does not on my board.

Additionally, after power cycling the board (it's externally powered by 24V; 5V is delivered via a buck converter to the Teensy) it seems to automatically start in the suspended state, with the 3.3V regulator off. The program button or the suspend resume button does not work to resume it.

When the Teensy is removed from the board (removing VBAT) and reinserted, it works normally. The suspend is only entered when power is removed from the overall board, and then reapplied later. The issue also appears to occur when the board is unpowered, Teensy removed and reinserted, and then powered again - signifying that something on system startup triggers suspend.

The issue does not occur without VBAT present.

The voltage on ON_OFF_SW with the Teensy is operating normally and the button unpressed is 3.28 V. Pressing it drops the voltage to .8 mV or so; holding it for four seconds suspends the Teensy. The voltage with the Teensy suspended and button unpressed is around 1V; pressing it again drops it to less than a millivolt. The Teensy does not resume from suspend under any circumstances; I have to power cycle the whole thing.

I should note that this pin is also wired to one of the Teensy inputs (pin 31), although it's not configured or anything. Perhaps this is related?

Here's the schematic:

 

[defragster]

Has worked when tried here since Beta 4.0 and 4.1.

The button to GND must not be going low enough? 1 mV doesn't seem like much - but something is keeping it from seeing the needed 'drop' to GND it seems.

In that state can a stronger GND path be applied to the pin using an alternative to the button?

Not sure sharing pin 31 is helping - something is feeding it enough power to not see the ON request - but doesn't stop it form seeing the OFF request ???

 

[waterlubber]

Has worked when tried here since Beta 4.0 and 4.1.

The button to GND must not be going low enough? 1 mV doesn't seem like much - but something is keeping it from seeing the needed 'drop' to GND it seems.

In that state can a stronger GND path be applied to the pin using an alternative to the button?

Not sure sharing pin 31 is helping - something is feeding it enough power to not see the ON request - but doesn't stop it form seeing the OFF request ???

1mV has got to be lower than whatever the threshold is on the reset pin. Additionally, the issue also happens somewhat intermittently with the battery removed; in this case, however, pressing the button to resume the system seems to work fine (so it's not a wiring issue, I don't think).
The 3.3V rail on the Teensy is isolated from the rest of the board, so I don't think there's any additional loads on it.

I'm holding Pin 31 in tri-state right now; I don't know if Teensy cycles its pins low during a reset cycle or something that would prevent a recovery.

Next time I get a chance I'm going to try driving the pin externally with another source and monitor the current. I'll also give it a shot with another Teensy, I suppose.

(By the way -- this board is quite extensive, but I'm refraining from posting the full schematics because they have my personal details everywhere. If you'd like more details, please send me a PM.)