ULPM LED weirdness

Hey everyone,

I’ve been playing around with ultra low power mode on the mangOH Yellow and have noticed some strange behaviors. I’m trying to troubleshoot an issue with a custom IoT module and I found these weird symptoms. I was wondering if anyone has any ideas what’s going on here.

Without any IoT card inserted – if you touch the mangOH Yellow in the area near the power switch when it’s in ULPM, the power light blips on 3 times in approximately 1 second intervals. It looks like VCC_5V0 is trying to turn itself back on?

With the custom IoT card inserted – sometimes the LEDs on the mangOH Yellow board stay on after it enters ULPM. It looks like maybe VCC_5V0_EN is floating or something? I noticed that enable line ends up going directly to a GPIO pin on the WP7702. Does the WP7702 maintain the GPIO output states when it’s in ULPM? I couldn’t find a good answer to that question in the product specification document.

Thanks for any ideas,

Did you modify your board in anyway?

I moved R607 to R608 to enable ADC3 on the IoT connector. I also moved R601 to R600 so I can supply USB_VBUS through the IoT card instead of the USB port.

Adding an external 1M pulldown on VCC_5V0_EN seems to somewhat help (seems to fix the LEDs staying on in ULPM, but doesn’t completely stop the blips when touching), but I’m not sure if there is a valid reason to be adding that or not…

Is any part of your iot card touching the yellow board? Maybe the SIM/SD card connector.

No, nothing is touching. As far as I know, we completely followed the IoT card spec requirements. We don’t have any components on the bottom of the board.

Is GPIO41 going to maintain its state keeping BUCK_CONV_EN low when the WP7702 goes into ULPM? It looks like BUCK_CONV_EN is floating in ULPM and allowing the 5V rail to sometimes turn on. Maybe I’m missing something? I can’t find anything in the datasheet saying what the GPIOs do when you enter ULPM.

sounds like it is floating…I’ll need to check,

@asyal Have you had a chance to look at this any more? At first glance it seems like it would have to be a problem caused by my IoT card, but all of my diagnostics point to the 5V rail being allowed to stay on when it shouldn’t

@asyal Any updates? This is a pretty big deal for us, I’m kind of scared of putting our stuff in the field knowing that the battery is draining faster than it should

It’s floating.
Can you DNI BUCK_CONV_EN resistor R904? System should work seamlessly without it being present.

Hi @asyal,

Thanks for your response. I just removed R904. The system still works fine, but the LEDs are still staying on when it goes into ULPM. Any other ideas to try?

what particular LED is staying on in ULPM? We dont see any LED on in ULPM.

All 3 of the LEDs stay lit up (which is really more than 3 because they are multi-color):

  • D401 is yellow I believe
  • D402 is on
  • D500 is white

The only logical conclusion I can reach is that VCC_5V0 is still turned on

We dont get that on any of our units. It seems the mod you made introduces the problem.
Can you double/triple check your R600/R601 mod?

Hi @asyal, I really appreciate you looking into this. I just don’t know what to do next. I triple checked all of our mods (R601 -> R600, R607 -> R608, remove R904) and took pictures as I checked them. Obviously we also remove the jumper on CN801. Earlier I talked about adding a 1M pulldown that seemed to help, but that was on a different board so I’m working on a fresh one now without that mod.

Here are the pictures to verify that we did the correct mods:

R601 -> R600:

R607 -> R608:

Removal of R904:

Just tested again this morning, and the LEDs all stayed on when it went into ULPM. I can’t remember if I’ve mentioned it, but it’s running from a LiPo battery when this happens, if that’s relevant at all.

Do you have a fresh board? Are you running stock firmware?
Can you measure VGPIO on R200 when its not in ULPM and when it is ULPM?