AN001 - Basic SoM Design
This application note is a simple SoM base board. Like a Boron it can be powered by LiPo battery, USB, or an external DC supply. It includes:
- RGB LED
- bq24195 PMIC
- MAX17043 Fuel Gauge
- USB Connector
- LiPo Connector (JST-PH)
- M.2 SoM Connector
This is the basic set of features you'll probably want to include in a LiPo battery-powered design. The Evaluation Board is also a good reference to use. This design, however, is simple enough that it can be hand-assembled, though you still need a reflow oven and some of the parts (in particular the fuel gauge and PMIC) are tiny and there are a lot of them.
This board a two-layer circuit board so it can be manufactured inexpensively and edited using the free version of Eagle CAD.
As this board doesn't really do much, you'll unlikely use it as-is, but you can use it as a tutorial for how to hook up the PMIC and fuel gauge.
There is another design in the SoM first board tutorial that includes additional information that will be useful for building your first board.
- bq24195 PMIC
- XCL223 3.3V regulator
- M.2 SoM connector
- RGB LED, reset, and mode buttons
- Micro USB connector
- JST-PH battery connector
- External power input (3.9V - 12V)
- Charging LED
- MAX17043 fuel gauge
While the pictures show a simple M3 screw and nut to hold down the SoM, the Eagle files have been updated with a proper standoff assembly. This is described in detail here.
This is the M.2 connector, RGB LED, RESET and MODE buttons, and USB connector.
The bq24195 PMIC circuit. You can use a different PMIC, however you'll need to manage its settings yourself as Device OS can only configure this PMIC automatically. If this PMIC is not present, then it will assume you're managing your own PMIC, or you do not have one. For example, a device powered only by USB or disposable batteries would not need a PMIC.
The XCL223 3.3V regulator. This regulator is required when using 3.7V LiPo batteries because they can have a voltage as high as 4.2V during charging. With some other types of batteries that never exceed 3.6V at any time, you can omit this regulator as the nRF52840 can be used at up to 3.6V on the 3V3 pin.
The MAX17043 fuel gauge. You can use a different fuel gauge, however as of Device OS 1.3.1, you cannot hook an alternate fuel gauge into the system so the battery reports correctly with device diagnostics. This is planned for the future.
The bill of materials for this board is:
|1||150Ω resistor 0603||Panasonic ERJ-3EKF1500V|
|1||332Ω resistor 0603||Panasonic ERJ-3EKF3320V|
|5||1K resistor 0603||Panasonic ERJ-PB3D1001V|
|2||4.7K resistor 0603||Panasonic ERJ-PA3J472V|
|1||5.6K resistor 0603||Panasonic ERJ-3EKF5601V|
|5||10K resistor 0603||Panasonic ERJ-PA3J103V|
|1||0.001 uF capacitor 0603||Murata GRM1885C1H102JA01D|
|1||0.047 uF capacitor 0603||Murata GCJ188R71H473KA12D|
|1||0.01 uF capacitor 0603||Murata GCM188R72A103KA37J|
|1||0.1 uF capacitor 0603||Murata GRM188R71C104KA01D|
|2||1 uF capacitor 0603||Samsung CL10B105KA8NNNC|
|2||4.7 uF capacitor 0603||Murata GRM188R60J475KE19J|
|7||10 uF capacitor 0805||Murata GRM21BR61C106KE15L|
|1||2.2 uH inductor 1008||Bourns SRN2512-2R2M/||$0.31|
|1||RS1JFP Diode||On Semiconductor RS1JFP||$0.44|
|1||bq24195 PMIC||Texas Instruments BQ24195LRGER||$2.93|
|1||XCL223 3.3V Regulator||Torex XCL223A333D2-G||$2.63|
|2||4.5mm tactile switch||E-Switch TL3305AF160QG||$0.20|
|1||USB micro B connector||Amphenol FCI 10118194-0001LF||$0.42|
|1||RGB LED 4PLCC||[Cree CLMVC-FKA-CL1D1L71BB7C3C3](https://www.digikey.com/product-detail/en/cree-inc/CLMVC-FKA-CL1D1L71BB7C3C3/CLMVC-FKA-CL1D1L71BB7C3C3CT-ND/9094273 CLMVC-FKA-CL1D1L71BB7C3C3)||$0.19|
|1||Red LED 0603 5mA||Lite-On LTST-C193KRKT-5A||$0.41|
|1||M.2 connector||TE Connectivity 2199230-4||$1.42|
|1||M.2 standoff||JAE SM3ZS067U410-NUT1-R1200||$1.25|
|1||M2*3 screw w/4mm head||example|
The eagle directory contains files for Autodesk Eagle CAD 9. It is a small two-layer board you can view and edit it with the free version of Eagle CAD.
- SomTest1.sch - Schematic
- SomTest1.brd - Board File
- SomTest1v4.zip - Gerbers
- SomTest1.lbr - Library file containing all of the components on this board
- SomTest1-brd.pdf - PDF version of the board
- SomTest1-sch.pdf - PDF version of the schematic
The Gerber files were tested at JLCPCB but were created using the default Eagle CAD settings so they should work with many fabrication houses.