PCB review nrf52832

Question

nrf52832_qfaa_dcdcN.SchDoc nrf52832_qfaa.PcbLib nrf52832_qfaa.SCHLIB nrf52832_qfax_dcdcN.PcbDoc

Hello, please review my PCB design for the nrf52832 soc. I think I've included all the necessary files, but let me know if you need anything else or something in a different format. 
 I used the nrf52832-QFAA Reference Layout DCDC as the base design for the PCB. 
 
 The changes I made were: 
 
 1.) Adding a 3.3V CR1632 battery to supply power to the 52832 as well as the PCF8523 
 2.) Added the PCF8523 RTC based off of the attached reference schematic from the adafruit PCF8523 development kit ( https://cdn-learn.adafruit.com/downloads/pdf/adafruit-pcf8523-real-time-clock.pdf ). Pin P0.22 will be configured SCL and pin P0.0.23 will be configured to SDA. 
 3.) Added a 5 pin header with connections for SWDIO, SWDCLK, VDD, GND, and Pin P0.14. 
 4.) Added a circuit to allow for attachment of a switch across pins 1 and 2 which will pull pin P0.14 to GND to use in software as a button press active low. 
 
 The overall goals are: 
 
 1.) Power the entire circuit and RTC with the CR1632 battery 
 2.) Use an external switch attached across header pins 1 and 2 to pull pin P0.14 to GND 
 3.) Get the time from the PCF8523 RTC upon button press over TWI using pins P0.22 and P0.23 as SCL and SDA 
 4.) Send the time over BLE 
 5.) Be able to program using header pins 2,3, 4 and 5. 
 
 Questions: 
 I know that it should be possible to program the chip with GND, VDD, SWDIO, SWDCLK but what programmer is specifically used for this type of programming? And is there functionality to program with this in Segger embedded studio? 
 
 I want to test the power consumption with the power profiler kit. It looks like the nrf52DK uses DCDC as its power regulator, so would testing the development kit power consumption be mostly representative of the power consumption of this PCB? How similar would the power consumption be between nrf52DK and this PCB? 
 
 I was looking into part sourcing and the X2 oscillator has 4 pads and is listed as XTAL SMD3215. I wasn't able to find any parts matching this description and was wondering if there was more information on sourcing a similar part. I was also wondering how closely the tolerance would have to match if an oscillator was substituted. 
 
 I also noticed that there wasn't a size description for the oscillators. Is this listed anywhere? I wasn't sure how to source the oscillators otherwise without replacing the footprint/pcb. 
 
 Thanks!

Kaja · Accepted Answer

For a chip antenna, you would need a fill pi-network for impedance matching, so the schematic should look like this: (meander, inverted F..+++ and chip antennas) 
 
 jake11212 said: Also for the trace antenna, can it just be created in altium by adding a trace as you would between any other components? Or is there a feature specifically for trace antenna drawing? 
 You can copy it directly from the DK, just add some mm to the length, for antenna tuning.. or see how to design your own in our whitepaper 
 Antenna choice is complex and depends on many factors including technical and commercial considerations. Here are some alternatives, and some considerations: 
 Monopole, printed PCB antenna: This is easy to make and easy to tune, you also only need one impedance matching component, so it’s cost effective. Here the spacing is the issues, you need to make it about 23 mm long needs a minimum of 5 mm clearance to the ground plane. High bandwidth, making it fairly resistant to detuning. Link to our whitepaper: https://infocenter.nordicsemi.com/pdf/nwp_008.pdf?cp=12_18 
 
 Meander antenna, printed PCB antenna, ex. our dongle antenna design: Requires a smaller area than the monopole antenna, but usually requires a pi-network for tuning in addition to length. Lower bandwidth than a quarter wave monopole antenna. Here is a link to our nRF52840 Dongle design files as an example of this: https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF52840-Dongle/Download#infotabs 
 
 Chip antenna: Higher BOM, but the antenna is small. The downside is that it usually has less gain. It requires a matching network, based on the vendors recommendations. It has a lower bandwidth than a quarter wave monopole antenna so it can be sensitive to detuning. Considering your target of a very small form factor a chip Antenna makes sense but reducing antenna size most often results in reduced performance. Some of the parameters that suffer are: 
 
 Reduced efficiency (or gain) 
 Shorter range 
 Smaller bandwidth 
 Distorted radiation pattern 
 More critical tuning 
 Increased sensitivity to component and PCB spread 
 Increased sensitivity to external factors (“body” effect, ground plane etc.) 
 
 It is often better not to reduce antenna size too much, if you can avoid it. 
 We do not recommend specific chip antennas, and the selection will depend very much on the end application design. The antenna vendors can assist on choosing the right antenna for a specific design, for example Johanson has a useful tool that helps with this selection: https://www.johansontechnology.com/chip-antenna-selection 
 
 Best regards, Kaja

PCB review nrf52832

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