nRF52 not booting properly without reset

RE: nRF52 not booting properly without reset

ovrebekk — Thu, 10 Aug 2017 08:38:32 GMT

If you are unable to figure it out Dajgoro you can attach your layout files (Gerbers) and maybe a picture of your board to us. Then we can have a look at the design and see if it looks OK.

Best regards

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Wed, 09 Aug 2017 20:03:52 GMT

I think there isn't much I can do at point. Good luck with troubleshooting your PCB.

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Wed, 09 Aug 2017 14:17:22 GMT

Even tho its only a 2L board, I have the most of the bottom layer as ground plane, actually I only have a few short traces which act as jumper, all of the traces are on the top layer. The load should be well below of what the PMIC can handle, so that should not be an issue. I'll try investigating how exactly is the interference manifesting, and I'll probably put some sort of filter at the sensor power supply.

Thanks for the troubleshooting help!

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 23:40:15 GMT

Glad that you found the issue. One thing that comes in mind is the gnd plan. You may not have enough via or floating island some where. Second thing that comes in mind. Check also that the PMIC has enough power to drive everything at once. Make sure you don't draw more than 80% of max capacity.

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Tue, 08 Aug 2017 21:19:47 GMT

I added decoupling as recomanded, and followed the layout design guides, and placed the PMIC close to the MCU. I've tried soldering, resoldering most of the components, but the issue persists over multiple boards. VDD level is 3.3V, but when using the PMIC switching regulator its 2.5 which I can then adjust via I2C. But that does not seem to have any effect on the issue. After BLE is initialized, there is a 50mV spike occurring at a 45ms interval. And as I was typing this, I went to chase that 50mV spike down, and I found the culprit. I have a VCNL4040 proximity sensor, and when it is initialized, the IR led somehow creates enough interference to glitch the BLE radio. Funny thing is on the old version I had it as well. Now I have to test the other boards too which I did not butcher while experimenting.

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 20:36:03 GMT

Check if you got VDD stable, enough decoupling caps. What is your VDD level ? Any soldering issue ? Any residual flux on the pcb. Have the board cleaned to remove all flux that could stuck under the IC. Check also if SWDIO or SWDCLK got pulled down at any instance after power up?

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Tue, 08 Aug 2017 20:25:19 GMT

I tried a 20k pullup, then I also tried a 6.8nF cap which is just enough to straight out the bouncing, but keep the timing, and it did not help. Then I cut the trace to the PMIC chip, and the issue is still there, there is probably more to this. Now I'm trying to disable the reset input, but removing "CONFIG_GPIO_AS_PINRESET" does not seem to help.

When checking the signals again with the pmic trace cut, the signals look identical to the old version of the board, but the issue still persists.

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 19:50:44 GMT

Have you tried a 15K pullup on that pin ? It shouldn't bounce like that.

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Tue, 08 Aug 2017 19:33:17 GMT

VCC comes first, after about 2ms reset goes high, then low for about 0.5ms, then high and low again and then it stays high. Something like this:

RST 0000000000001010111111

VCC:0000111111111111111111

On the old version, reset goes high 1.2ms after power up, and stays high, very sharp rise time, no oscillations.

When I add a pullup, VCC and RST ramp up simultaneously.

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 19:14:44 GMT

In that case, the only way to know what is happening to that pin is to hookup the scope and see if it ever goes down to zero or not and when related to VDD. You'll need 2 probes.

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Tue, 08 Aug 2017 19:07:36 GMT

Yes, I thought about that too, that's why I tried adding a large capacitor to keep the line low until power is achieved. I tried various values, from nano farads to 470uf which takes a while to start up, always the same thing. I even left the old voltage regulator as a backup that was on the previous version, and its the same thing.

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 18:51:40 GMT

Then i suspect that the BQ25121 pulls the reset before power good for the nRF or some timing related to that.

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Tue, 08 Aug 2017 18:36:26 GMT

Even with the internal pullup I still measure VCC voltage, and adding pullup did not help.

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 18:15:08 GMT

the internal pullup is too weak for open drain. The capacitor does not help in this case.

RE: nRF52 not booting properly without reset

Dajgoro Labinac — Tue, 08 Aug 2017 18:05:56 GMT

I did, does not help. The nrf52 has a internal pullup so its not needed anyway. I even tried adding a 470uF cap to the reset line to hold it low for a few seconds after power up, and the issue persists, even then I have to short the reset line to get it working properly.

RE: nRF52 not booting properly without reset

Nguyen Hoan Hoang — Tue, 08 Aug 2017 17:23:29 GMT

Try adding a pullup resistor. I believe open drain requires external pullup