Hi all!

In this log I'm going to go over my methodology for component selection. I will explain what subsystems I want to include on StampPD, component requirements, other influencing factors, and a summary of component restrictions. In the next couple logs I will go over each sub-system of the board component by component to explain my part choices. I hope to show how I went about component selection to give new PCB designers an idea of how I approached this this design as well as receive feedback from more experienced designers. I have minimal experience with power design so I'm sure I've made mistakes somewhere here! 

Board Subsystems

There are 5 main parts of StampPD:

• PCB Stamp
• USB PD Controller
• USB ESD Protection
• 5.0V Regulator
• 3.3V Regulator

These 5 parts are combined together to create the stamp. Only two of these sub-systems are absolutely necessary, the PCB and the USB PD Controller. The USB ESD Protection is nice to have but is optional. Being only a single component (TPD4E5U06DQAR) it would be easy to remove. The 5.0V and 3.3V Regulators are also nice to have but could be removed if needed.

Part Requirements

There are a couple requirements I've put on the design that influence what parts I want to select:

• Hand Solderability
  • I want to be able hand solder the parts if possible. This means that I need to put a limit on the smallest parts can be
  • While some parts like the USB PD Controller (AP33772S) are not very hand solder friendly, I think it should still be possible
  • This needs to be balanced with the size of the PCB itself
  • The smallest size I feel comfortable hand soldering is a 0603 so that is my designated minimum component size
• Cost
  • In my design objectives, I stated that I don't want to spend more than $20 for 5 boards. This means that parts for the boards should be less than $20/5 = $4 a board.
  • I am not including the cost of the PCB
  • I am not including any reduction in part cost when buying parts in bulk
• Castellated Holes
  • Since this is a solderable stamp, the PCB will need to have Castellated Holes on the edges
  • Castellated Holes are through whole vias that have been cut horizontally in half through edge cuts on the sides of the PCB. This exposes the inner copper of the via, making it easier to solder to a pad
  • This will increase PCB cost. JLCPCB shows an additional cost of $39.30 for 5x 100mmx100mm for 4 edges without a gerber file. Changing the number of edges does not change the cost very much ( < $2).

Other Influencing Factors

I have some personal external factors that also limit my part selection:

• JLCPCB PCB Assembly (PCBA) service
  • I've wanted to try using JLCPCB's PCBA service and thought this board would be good to try it on
  • This limits my component selection to JLCPCB's catalog of components as well as using JLCPCB PCB's
    • This may influence component cost as there will be fewer choices
  • If this service proves to be too expensive then I will assemble the PCB's myself
• Reduction in unique components
  • I want to have the fewest number of unique components possible. This will help reduce complexity, component sourcing, and component confusion, especially if I hand assemble boards
• Availability of components
  • I want to make sure that JLCPCB has enough components in stock to not worry about running out of components
  • This makes it easier for others to manufacture my design directly through JLCPCB like how I have without any changes
• Power LED's
  • I want to make sure that users know when the StampPD is connected and on
  • I will be adding an LED for power from the USB PD lines directly as well as power from the USB PD Controller
    • This should help identify if power is flowing through the USB PD lines and to the USB PD Controller with just at a glance

Summary of Component Restriction Decisions

Here is a summary of the restrictions that I have put on component selection:

• Minimum component size of 0603
• Less than $4 per board in component cost
• PCB must have Castellated Holes
• Components must be available through JLCPCB's PCBA catalog
• Unique components must be minimized
• All components must have significant quantities available
• At least two LED's must be on the design

Finally, here's the latest Schematic of the StampPD. In the next log I'll go over the 5.0V and 3.3V Voltage Regulator part selection on a component by component basis to explain how each component was chosen.