This post has been in my evernote for a week now due to internet issues at home. I will have another update in a day or two. I may not get all the parts in time so I am moving to plan B to make the prototype using the EVAL Module. Never the less, I am putting up this little doc for reference.
The background bits
The proposal for this roadtest plus was written around the TI TPS92512 which is an LED Driver Buck converter. The idea was to design a 4Channel Lighting solution along with a variety of LED panels. In addition to RGB Lighting Panels, it was proposed that custom ones can be made using special LEDs for agricultural lighting more commonly known as ‘Grow Lights’. Additionally, the control over the colour as well as intensity of the lights should be controllable over say Wi-Fi which can be accomplished by using a CC3200. The system is to be designed in an enclosure that can replace the conventional home or industrial lighting hence the title “Multipurpose Modular Light Bar Project”.
I received the kit from e14 and placed an order for required parts with them as well. Till now I have received some bits from the good people of WE and I will be doing a thank you post separately for them. In this episode I have a few updates that take my little project a few baby steps ahead.
The PCB making for TPS92512
Designing a PCB is not the toughest part of the design but rather making it work. It takes time to get analog designs to work. In this case, I already have a reference design for the TPS92512 which is the EVAL module supplied. The part can be hot aired by hand BUT the 0603s are a bit difficult unless you have a reflow oven. I have used the SLVUAC9A documents as a starting point and am using CadSoft Eagle to make the PCB where I am using the schematic as well as the basic layout.
In order to start the schematic, I need all the parts. I already have my favourite resistor and capacitor parts in eagle and of this exercise I have made all the resistors and capacitors 0805s except for the input 4.7uFs which are 1210s and 1208s. The TPS92512 is a different story because I clearly do not have the right part. The logical solution is to make the part OR...
Using Ultra Librarian.
TI provides footprints for most of their parts however these are not in the standard format. Instead they are downloadable as a script type format. I have not gone into the details of it but there is a tool called ‘Ultra Librarian’ which can be used to convert that script into a file digestible by Eagle, Altium and Orcad Etc. Here is what it looks like...
I Just pointed it to download file and it created the footprint script in it’s folder.
I still need to create a schematic symbol using Eagle’s library system and I just created a new library and a new schematic symbol. However I later found out I do not need to do that either... the script creates it for us so...
Cool! Next the footprint. For that I simply ran the script and it created three footprints in the library. The different variants of the footprints can be google if you need more info but the next step here is to connect the pins on the footprint and the symbol.
Creating a new package will introduce the screen to connect the schematic with the footprint and with that step out of the way, we can start with the schematic
Making the schematic
I created a new project in Eagle and a new schematic where I first added all the parts and then connected them up. I won’t waste your time with the details but it was pretty straightforward. Here is the schematic finally.
That takes care of the schematic and with eagle if you create a board, the parts from the schematic are automatically placed in a corner. Since the objective of this exercise is to create a small PCB, hence we next move to the layout.
Making the layout
Looking at the reference design, I placed out the components in a similar fashion. But I am not yet happy with it. I still need to experiment and give it a bit of time. This will be continued next time.
The resistor values used are very specific and I am looking into the design seminars on choosing the values to see if I can substitute the values. The current sense resistor of 0.2Ohms is a bit pricey and I seemed to have forgotten about ordering it. The next step is to send the PCB to the fab house for getting the blank PCBs made. I am still verifying the layout for mistakes and should be able to send it pretty soon.