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.
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…
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.
@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
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?
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:
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.
Two years later I was experiencing similar more potentially damaging issues whilst attempting to reduce the 200mA Idle current drawn by the mangoh yellow - for interest the WP7702 idle is >3mA
Turns out that my mangoh yellow has both R908 (supposed to be a NF) and R907 fitted
Not a great combo if you also fit R909 - it connects 3V7 to 1v8 via a resistor
Note that VGPIO is off if the WP is off - there is no way to POWER_ON_N the modem if U901 is OFF. and no way to connect something external to the WPs POWER_ON_N.
