Hardware design and antena

[FormerMember]

Designing a custom pcb, we have a few questions, and maybe you could help a little bit.

On this Nordic design ,before proceeding to layouts :

1. Can I skip pins 45/46/47 and not puting L2/L3 ? I did not see them on other designs.(what are they?)
2. If I won't use NFC, can I skip all the parts on pins 11/12 and simply use them as outputs ?
3. Can we locate the chip on one pcb side and the antena right on the other side beneath the chip? ( extreme size constrains on pcb..)
4. Can I flash this design using nrf52 dev kit on the debug connector ?

Are there any specific pins that can't do specific things ? (I could see serial/I2C/SPI/PWM works on all of them)

Thank you !

[WestCoastDaz]

Rani,

1. Pin 45 is VSS, ground, so you definitely need that. Pin is the output of the internal 1.3V LDO which needs to be decoupled. Notice that cap is connected between it and ground. Pin 47 is the output of the internal DC/DC and L2 and L3 are required for this. If you are not using the DC/DC in your design then you may be able to remove L2 and L3 but check with Nordic first.

2. Yes, you can use pins 11/12 as GPIOs but you need to use a special define in your code since they default to NFC control. Its CONFIG_NFCT_PINS_AS_GPIOS.

3. That you will have to check with Nordic on. If you do this you will likely have to due RF-PHY testing to get SIG certification since you have changed from the reference design.

4. Yes, you can flash this chip using the Debug Out connector on the DK. Note the supply voltage of your board has to be 3.0V to be compatible with the DK.

The only special pins other than the power and antenna pins are the analog pins and the debugging pins.

Hope this helps, Darren

[FormerMember]

Help indeed ! thanks. regarding pins 46-47 , if you look at Sparkfun design of the chip (a well known company) here you will see they took out L2/3 . Anyway I am not sure I understand this point. Do I need the internal LDO ? should I use external one for 5V inputs or can I use the internal ?

[WestCoastDaz]

Rani,

Looking at the Sparkfun schematic at the top of the nRF5832 block you will see it says supply range 1.7V to 3.6VDC. The chip can ran from range. Internally the chip uses an LDO to reduced the voltage to the radio and CPU core. So yes you need the LDO. But from their schematic you can't use the internal DC/DC which can help improve efficiency when the radio is on when running from a high supply voltage.

Also the nRF52832 doesn't have 5V tolerant inputs. The maximum I/O input voltage is VDD + 0.3V when VDD is <= 3.6V. Again this is listed in the data sheet.

See section 17 of the datasheet infocenter.nordicsemi.com/.../nRF52832_PS_v1.3.pdf

Cheers, Darren

[Jørn]

Hello rani

1.As Darren Beckwith mentioned the inductors L2 and L3 are needed for the DC/DC regulator, see page 78 of the nRF52832 product specification. These can be omitted if you are not using the internal DC/DC regulator, see the reference schematics pages 545 and 546 of the product specification.

See edit below

3.Yes it is possible to do that, see devzone.nordicsemi.com/.../ The environment of the antenna, as well as the via hole will affect the impedance observed at the output of the T-network, and a matching network is needed to compensate for this. If you are using a PCB trace antenna you can use a single shunt capacitor in combination with tuning the antenna length. If it is a chip antenna (as in the link) you will need a pi network. See the following blog post and the links provided there. devzone.nordicsemi.com/.../ It is for the nRF51 but the antenna matching methods still applies.

Also be sure to read the PCB guidelines, page 551 of the product specification for considerations when doing the layout.

EDIT: 26.04.17: As pointed out in the comments by dingari I may have misunderstood the question in the original post. Placing the antenna directly below the chip really isn't recommended as the antenna needs a keep-out region around it, meaning no traces, or components on any layer on the PCB within a certain distance from the antenna. In the case of a PCB monopole, there should also be a ground plane reaching out from the feed point of the antenna. This ground plane should be as whole and large as possible. Please see the white paper on monopole antennas for 2.4GHz infocenter.nordicsemi.com/.../nwp_008.pdf

Best regards

Jørn Frøysa

[dingari]

Regarding #3, I think you misunderstood the OP. He is asking whether it's possible to locate the antenna directly below the nRF5 chip. Every antenna datasheet I've looked at requires no ground and no traces of any kind below the antenna.