nRF5340 DECA / DECN Pins (Bypassing)

[sanderson]

What is the purpose of the external capacitors on DECA and DECN?  DECA calls for 1uF and DECN calls for 0.1uF.  The datasheet calls these out as "Regulator Supply Decoupling".  Are these bypasses on the input side of the switching regulators?  We have a compact layout, and I'm trying to determine the priority of these bypasses in terms of which ones need to be closest to the pins.

Also, I would like to use a 0201 capacitor on the DECA pin for the 1uF.  Due to derating of the small package sizes, I was going to use a 2.2uF/0201 part there but wanted to know if there are any minimum/maximum capacitance requirements for the DECA pin.

Lastly -- the 2.2nF capacitor on the DECR/DECRF node.  Is that intended to be located as close as possible to the DECRF pin?

We are using the WLCSP package.

Thanks!

[JONATHAN LL]

Hi Scott, update time!


Capacitors on DECA, DECD, DECN, DECR/DECRF are decoupling on the output of the regulators, both LDO's and switching regulators. 

Lastly -- the 2.2nF capacitor on the DECR/DECRF node.  Is that intended to be located as close as possible to the DECRF pin?

Yes the 2.2nF capacitor should be mounted close to the DECRF pin.

Due to derating of the small package sizes, I was going to use a 2.2uF/0201 part there but wanted to know if there are any minimum/maximum capacitance requirements for the DECA pin.

The 2.2uF seems indeed to be a good choice, so this is ok. 


We do have a withe paper Power Supply Decoupling Capacitor Selection (nordicsemi.com) that you might be interested in. 


Note: We also do HW reviews and give feedback so if that is something you want then you can create a private ticket and call it HW review request nRFXXX.

Regards,
Jonathan