Design with nPM1100, nRF5340 and nRF21540 Schematics and PCB for single antenna based on Thingy53


I'm designing a drone based on these three Nordic IC:

  1. nPM1100
  2. nRF5340
  3. nRF21540

Let's Start with nPM1100:

Based on this Reference circuitry

I based my design on Configuration 3:

This is my schematic on KiCAD

I connected VTERM to VPP
However, checking the schematics on the Thingy53 I see the VTERM Connected to GND:

Is there any particular reason the VTERM is connected on GND instead of VPP?
Furthermore, I see both VOUTBSET0 and VOUTBSET1 connected to DEC. This should be any problem cause internally DEC is connected to VSYS:

For this PCB connection I wonder is the GND plane around the nPM1100 is ok or needs to be clear out a little bit?

About the nRF5340 the questions I got are related to the RF signal connected to nRF21540.

nRF5340 schematic:

nRF21540 schematic:


These components are placed quite close together.
I'm been tinkering around the RF signal width base on different stack up
My current stack up is this:

KiCAD calculator indicates this for Microstrip Line:

And this for Coplanar Wave Guide:

And this for Coplanar Wave Guide with ground plane:

I think I should use the last one because I got a 4 Layer PCB with GND plane just below RF signal plane, however I'm not sure about the trace width.


About nRF21540 both schematics and PCB for single antenna.
Checking the documentation on

I see two things I want to validate

First the resistor R1/33k connected in serie with MODE pin.
Checking this documentation Errata:

I decided to go for option Number 2 and connect the MODE pin to GND.

The second thing that got my attention is the 50R resistor connected to the ANT2.
Based on Thingy53 schematics:

I wonder if the LC network connected between the 49R9 and the ANT2 is mandatory or it's something I don't really needs for my design.

About the Chip Antenna, the Thingy52 use a different SMD Chip Antenna

I wonder if the Chip Antenna 2450AT18B100 can be used with the nRF21540 or should I change the Chip Antenna for WLA.01 used on the Thing53?:

Furthermore, Is needed the RLC network connected after the MM8130-2600, even when I don't use that connector on my design?

Lastly, the PCB components placement for LC network connected to ANT1 and ANT2:
The Thingy53 got this PCB design:

I currently have this one:

Should I move the LC network move down or should I keep it as it is?

Thanks and Best Regards,

Jose Pablo (JP) Castro Valverde

  • Hi Jose,

    I will look into this and get back to you with a response.

    Best Regards,


  • Hi Jose,

    Regarding the nPM1100, since you are using the Configuration 3, here it's in normal configuration, and the Vterm threshold should be set to HIGH, which is why it's connected to VPP. But in the other configurations, it's threshold is set to LOW (as it's in minimal configuration), which is why it is connected to ground. You can refer the VTERMSET for details.

    As for the DEC and VSYS pins, they are not internally shorted (well, they are connected...) but the VINT that is generated when the SYSREG is enabled is the internal supply for the device and this VINT is taken out through two pins, DEC and VSYS. The DEC is used to for Buck output voltage selection. So, if both VOUTBSET0 and VOUTBSET1 are connected to DEC, this means, they are both HIGH and the VOUTB (buck output voltage) is 3V. But as per configuration 3, the VOUTBSET1 is connected to GND. So the VOUTB is 2.1V. You can refer the Buck Regulator for further details.

    For this PCB connection I wonder is the GND plane around the nPM1100 is ok or needs to be clear out a little bit?

    Is your GND on inner layer or outer? Looks like it could use more GND vias to other ground planes.

    Hope these help for the time being and I will look into the rest and get back to you soon.


  • Hi  ,

    I've been doing some changes based on Manufacturer feedback. 
    I got 4 Layer stack up (TOP: Signal, GND:Mixed, VDD, BOTTON:Signal).
    I got some updates on the design to make, as soon as I make those changes I'll let you know, I got more questions related to nPM1100 and the other Nordic's IC as well.

    Best Regards,

    Jose Pablo

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