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PCB Variations

A project log for FrSky SmartPort Inverter

A compact hardware solution for interfacing the FrSky SmartPort to a F4 (or possibly other) flight controller.

Bud BennettBud Bennett 07/30/2018 at 14:100 Comments

I got a suggestion for two variations of the SmartPort Inverter -- one with all the components on a single side of the PCB (for easier soldering), and another single-sided variation that uses the DMN601DMK part, which includes both MOSFETs in a single SOT23-6 package. I spent some time on each of these designs with varying results.

Two-sided to Single-sided Conversion:

There is no way to prove that any particular layout is the absolute smallest possible (IMHO). I spent as much time as I was willing to create the single sided PCB below.

The components could probably be packed a bit tighter, but it might make soldering more difficult. As it is, the PCB is quite a bit larger than my original 2-sided PCB at 0.37 x 0.38 inches (9.4 x 9.7mm) -- 3 boards will cost $0.70. If you wish to make this board be aware that I have not made one myself, but it is checked for design rule errors and connectivity. One benefit to a single sided PCB is that the pad labels are placed on the back side, which makes it easier to connect the wiring harness.

Another version for the DMN601DMK:

The DMN601DMK is a part that includes 2 MOSFETs in a single SOT26 (SOT23-6) package (There are other dual MOSFET parts that might be suitable as well). The thought (not mine TBH) was to make a single sided PCB as small as the double sided PCB. I had two objections to this approach: multiple components in a single package are sometimes more difficult to hook up efficiently and may not lead to the smallest layout area, and there is a possibility that the package could be rotated 180° when soldered. Both of these concerns were unfounded. 

The package and schematic for the DMN601DMK is shown below. Note that the package can be rotated in either direction while maintaining the same connectivity. The pins are not even numbered in the data sheet. I did, however, have to create a new component in order to use this device in the schematic and layout. You can get this part from Arrow.com or Digikey in small quantities. (Note: The SOT363 is NOT the same package as the SOT23-6. The SOT363 is a 6-pin SC70 package with a pin pitch of only 0.65 mm vs. 0.95mm for the SOT23-6. It would be very difficult to hand solder the SOT363, but possible to hand solder the SOT23-6.)

Here's my final attempt at the PCB:

The back side is nicely labeled:

The PCB area is 0.33 x 0.33 inches (8.4 x 8.4mm), which is only slightly larger in one dimension than my original double sided PCB. 3 boards from OSH Park will cost $0.50 -- same as the double sided PCB.

I uploaded the gerber files to this  project's "Files" area if you want to make PCBs for yourself. Disclaimer: The design rules and connectivity  are without errors, but I have not fabricated these boards. Caveat Emptor.

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