Requirements and decoupling capacitors?

[Magnus Jonsson]

Hi

I try to find some suitable capacitors for decoupling the nrf52832 part. Is there any min and max values that must be fulfilled regarding DC and AC bias? Can I use the same values as in the nWP030 white paper about decoupling of the nrf52840 for VDD och DEC4?

Symbol	Description	Effective capacitance
		Min	Typ	Max	Unit
CVDD	Effective capacitance in VDD	2.7	4.7	5.5	µF
CDEC4	Effective capacitance in DEC4	0.7	1	1.3	µF

Best regards

Magnus

[Andreas]

Hi,

 

Yes you can use nWP030 as reference for nRF52832 as well. Note though that the VDD max spec does not apply to nRF52832.

 

Best regards,

Andreas

[wallance.lin]

Hi

I'm using nRF52840 and use 1u 10% 10V X5R + 47n 10% 25V X7R 0402 for DEC4 power rail, the minimum value will less than 0.7uF when considering DC bias, AC ripple , temperature, and tolerance. Do you have any concern to change 47n to 470nF? I find only this modification could meet the effective capacitance in nWP030 white paper.

[Andreas]

Hi,

 

As you say the 1µF cap will not be inside the specified range for DEC4 and should not be used. The 47nF is a filter cap and should not be increased to 470nF.

 

Best regards,

Andreas

[wallance.lin]

Hi 

Do you have any concern if the minimum effective capacitance of DEC4 is 0.5uF around? It is a corner value when considering all possible decay. Should I only need follow reference design? because Nordic already do verification on it, or I have to fine tune the typ. value of cap (maybe 1uF +??, keep 47nF) to make sure corner capacitance can meet the request from nWp030. My customer requests us to follow nWp030 to make sure no any risk.

[Andreas]

Hi,

 

The values in nWP30 is the specified requirements of the IC to which it is designed for and qualified against. 0.5µF is lower than 0.7µF, there is no guarantee that the IC will work as supposed if you violate the requirements.

 

Best regards,

Andreas

[wallance.lin]

Hi

thanks, what or where should I pay attention on when I do verification when raising 1uF to 1.5uF?

Best regards

Wallance

[Andreas]

Hi,

 

1.5µF is a bit high, I would rather choose a 1.0µF part that has low enough derating. You should verify voltage on DEC4, ~1.27V. Also overall performance, if this capacitance is not right the the IC will not work properly.

 

Best regards,

Andreas