The Reason for Inductors on Pins DCC and DCCH

[Styve Naoue]

Hello NordicSemi,

We are developping a product based on the nRF52840-QIAA and are using the schematic reference nRF52840 DK Hardware files which is similar to the circuit configuration no.4

Here the DCC  and DCCH pins are connected to GND via L2 (10uH) and L3 (15nH) and to power supply  via L4 (10uH) respectively. However, it is not the case in all other relay reference as in reference circuitary

we wish to know please, the benefits of using this inductors rather than leaving the pins floating or directly connected to GND and VDD respectively ?

Thanks in advance for you reply.

[Andreas]

Hi,

 

See the POWER section in the PS. The inductors need to be assembled in order to enable the on-board DCDC converter mode of the power supply. Pros of this is lower current consumption than the LDO mode it would otherwise be in, cons: external inductors. If you do not plan to use the DCDC mode, then leave the pins floating.

 

Best regards,
Andreas

[Styve Naoue]

Hello Andreas,

I have a follow up question about the inductors L2 and L3 in ref circuit no.4 for the nRF52840.

Why use 2 inductor for L2 = 10 µH Chip inductor, IDC,min = 50 mA, ±20 % and L3 = 15nH  High frequency chip inductor ±10 % instead of just one inductor component of L=10.015uH ? 

I believe with the given tolerance, inductivity between 8 to 12 uH is allowed right? 

Thanks again for the reply in advance.

[Andreas]

Hi,

 

The 10µH is the inductor used by the DCDC regulator, the 15nH is a RF-choke to limit the amount of high-frequency noise injected to the internal supply. These two components have different frequency characteristics, so it is not possible to combine them to one unfortunately.

Correct, 8-12µH is fine, but if you use a part closer to the edge (e.g. an 8.2µH), the tolerance must be tighter so that even the units that are on the limit are inside.

 

Best regards,
Andreas

[Styve Naoue]

Hello Andreas,

Thanks once more.