Decoupling capacitor values for nRF52

[jgartrel]

Hi,

I have read your guide for Power Supply Capacitor Selection: https://infocenter.nordicsemi.com/pdf/nwp_030.pdf

and the product datasheet v1.7 for the nRF52840 which were both quite helpful. I see that the recommended capacitor value for VDD and VDDH are 4.7uF and the product datasheet recommends a 100nF for DEC1.

I am a bit confused to see a "maximum" value listed for a decoupling capacitor.

1. What constraint drives the maximum value of the decoupling capacitors for the nRF52?

2. As long as the capacitors exceed the minimum values, deliver <50 mV AC rms at 1 kHz, sufficiently block DC, and provide all of those over the operating temperature range, is there any reason why we could not use a 10uF capacitor for each VDDH and VDD and a 1uF capacitor for DEC1?  Is there some other reason why these capacitor values would not work properly if used?

Thank you,

James

[Priyanka]

Hi James,

It's mainly a safe range that is mentioned. If the size of the capacitor increases, this can affect the start up times and also affect the Brown out Reset (BOR) behavior too. It can also affect the programming.

Best Regards,

Priyanka

[jgartrel]

What is the safe range for DEC1?

[jgartrel]

Also what is the critical timing requirements for startup and Brown out Reset that drive the sizing ratios of the decoupling capacitors for the board?  That would be helpful to know so that I can size them appropriately, especially in space and power constrained applications.

[Priyanka]

Hi James,

I am looking into this and will get back to you soon with a response. Please expect a slight delay as I am also looking int a few other cases too as we are short staffed at the moment due to the summer holidays here in Norway.

Thank you for your patience and understanding.

Regards,

Priyanka

[jgartrel]

Thank you so much for looking into this

[Priyanka]

Hi James,

The "safe range" or the "nominal values for operation" are what is recommended by us, i.e. the 100nF (with a tolerance of +/-10%). We always recommend to NOT CHANGE the cap value, but you are free to test it just that we will not guarantee the performance. 

Also, we cannot share further specific details regarding the design, other than what is available in the P.S and documentation.

-Priyanka