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nRF52832 IO problem

Hello!

We have nRF52832 chip on our product and we have some problem with one of its IOs.. We configured P0.16 as RX of UART, And when we run it we see this behavior of this IO:

VCC (yellow) vs P0.16 (green) that configured as UART_RX

Here we see that with rising of VCC (yellow signal) IO (green) rising to almost 1V when it supposed to still at 0V. Important note: we disable and enable VCC fast here so we see that before rising of VCC it don't have 0V. This behaviour is very problematic to our system. Because we have power supply sensitive sensor that connected to this UART. This spike of voltage damage sensor that connected to this IO.

We tried to load to evaluation board same version of SW on nRF52832 and we got next result:

We see that also here we have the problematic spike.

When we erased the evaluation board - we got the same result.

Is this IO known as problematic?

Thank you

  • Deriving the 3.3V Buck from the 9V Boost is an unusual choice and is likely to be both inefficient and troublesome; if that choice was made for sequencing then it would be better handled by deriving both regulators from the charger with an alternative enable/disable method for sequencing. Focusing on the sensor can you show what happens to the 9V as I recall you posted the sensor was an MSP430 so the interesting part of the circuit is not shown; also I can't make out the inductor shown on the sensor, is that a feedthrough or a real inductor? It's difficult to see the connection.. the sensor schematic would clarify these questions.

  • 1. Because of long delay between enable to booster and stable 9V (it is about 15 msec) and because short delay at 3.3V buck - less than 1 msec (you can see it at screenshot) we decided to drive enable to 3.3V from 9V and ensure they will rise at same time. At previous version of our board both - buck and boost was driven by charger. Here you can also to put attention that buck here also accept as input voltage - the power from charger. And only its enable is driven by 9V. 

    2. I can't show you what happening according to MSP430 because I don't have schematic of it. It is like black box for us and manufacturer of the sensor no published the schematic of it The only thing we know - the MSP430 get 3.3V from buck converter from 9V on sensor board. I shown before the relationship of 3.3V on-sensor and on-board. 

  • Here this screenshot again:

    Yellow is 9V, green is nRF 3.3V and blue is on-sensor buck 3.3V

  • Instructors on the schematic are ferrite beads for noise filtering

  • I would start by reducing R49 until the nRF buck supplies 3.3 volts at the same time or earlier than the MSP430 3.3 volts. Ensure the nRF does not sink a lot of power until the 9 volts has stabilised by inserting a time delay at the start of main() to ensure this. That at least removes some of the potential issues. meantime do you have a link to a datasheet on the sensor?

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