NRF52840: VDD ramp-up to main() time.

[Hrishi]

Hi,

How much is the expected time period from the time VDD goes above 1.75V to main()? I am using a custom bootloader and am seeing a ~4.5s (yes seconds!) delay in getting to bootloader main(). When the debugger is connected this time is in the 100s of ms, which is what I would expect without the bootloader on first power up (1.8V VDD rail starting up). Here's a scope shot of my 1.8V rail (CH2) starting up and the IO (CH1) toggling (one of the first things done inside main()). Any help is greatly appreciated.

Thanks.

Hrishi

[Kenneth]

Hi,

Do you see the same problem if you are using VDD = 2.0V?

Is this measured close to the VDD pin?

What is the content of UICR after power up? Type: 'nrfjprog --readuicr dump_uicr.hex'

Any schematic to share?

Best regards,
Kenneth

[Hrishi]

Hi Kenneth,

I can not try with 2V because this is in a system powered with a 1.8V regulator. As seen in my scope shot the bus looks clean.

I checked the UICR after power-up most locations are FFs except for some of the 'reserved for Nordic firmware design' locations below:

Does this tell you anything? Where else could I be looking to debug this issue?

Thanks.

[Hrishi]

I am using a BMD-340 module.

[Kenneth]

The only explanation I have is that something is charging up, e.g. that even if you supply 1.8V, you have some series resistor/diode that limit the current going to the nRF52840 thereby keep it in some kind of reset state. That is why I wanted you try to tweak up the VDD voltage a bit to see what happens. I assume you are not able to open the module to find the exact chip markings? 

[Hrishi]

These modules are using nrF52840-QIAA production release 1 silicon. BMD-340 doesn't have anything that would slow the VCC down by 3-4 secs.

I am sure I am missing something somewhere. Could there be something in the boot-up process that may cause a long delay? Although as I mentioned earlier if I use the debugger and run the bootloader project, I do not see this huge a delay.

Thanks.