nRF52840-QIAA Noisy VDD supply

[sammy91]

Hi there, I am using the MDBT50Q-1MV2 Raytac module, with the nRF52840, and i have noticed that I have a very noisy VDD supply pin. Which definitely a problem because measures very small voltages and is very sensitive to noise.

I have an external 3V LDO:

and I have tied VDD and VDDH together to disable Reg0:

Also, I have noticed that by, adding:

sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE);

causes VDD to change the noise to a 5mV 'chopping' triangle wave noise, but then depending on device operation jumps up to 15mV noise.

So my question is:

What connection + firmware arrangement for my nRF will provide the most stable VDD supply voltage (<1mV noise)?

Power consumption is not an issue.

[Andreas]

Hi,

 

The DCDC mode (REG1, apparently inside the module itself) has different output ripple than LDO mode. If power consumption is not important you should just use that. To further reduce noise you will have to experiment with various noise preventive measures on your PCB, e.g. decoupling and ferrites. Maybe a large cap on the 3VD net could reduce the noise somewhat.

 

Best regards,

Andreas

[sammy91]

Yes my board has a lot of noise preventative measures. My question is, what combination of using the Reg1 + Reg0 DCDC and/or LDOs will result in the lowest noise? Or should I turn them all off and only focus on my board's external supply?

Also, If i supply VDDH only, does that make VDD an output to supply the rest of my board?

[Andreas]

Hi,

 

I do not have a lot of data on this unfortunately, from what I can see REG1 = LDO, REG0 = disabled causes slightly less ripple than REG1 = DCDC, REG0 = enabled. Still, LDO will draw more current when switching on, so it might differ from design to design depending on the properties of the supply, but it seems to align with what you are seeing. Turning them both off means you will turn the nRF52840 off, any noise then will be contributed from other parts.

 

If you supply VDDH only you can use VDD to supply external circuitry. The internal regulator can supply up to 50 mA, so make sure you are not supplying a lot of current e.g. when using the radio.

 

Best regards,

Andreas