AWR1843AOP: Appropriate Decoupling Capacitor Placement in Layout Design When Supporting Multiple Pins w/ One Capacitor Part

Part Number: AWR1843AOP

Hi TI Expert,

Where do I place a decoupling capacitor when this one part is the single decoupling device for AWR1843AOP multiple pins?  For this question I am referencing the AWR1843AOPEVM schematic and layout design.  From sheet #4 of the EVM schematic, you have the image below.  C91 is designated to support decoupling for VNWA pins.  The 2nd image below is from sheet #4 of the EVM schematic as well:  This image shows the VNWA pins for which there are three pins and they are located in different locations on the device as shown in image #3 below.  Therefore, I have one decoupling capacitor to cover three pins in this case.  There are other cases similar to this.  Obviously there is limited space and it is not possible to route from this one device to all of these pins directly (There's too much other routing required that interferes w/ adding a trace to connect from this single capacitor to all three pins directly).  In looking at the EVM layout layers on the PDF document, it appears that C91 is only connected to one of these three pins directly.  How do you choose which pin to connect the capacitor given the capacitor is technically supporting decoupling for multiple pins?

  • Hello, 

    Please place the cap close to C1. On AWR1843AOP,  we try to and components and ground plane above and below the device to avoid surface wave artifacts. 

    -E. Shareef 

  • Is there a guide for similar instances of this same issue on which pin to place the decoupling capacitor close to in cases where there are more pins than decoupling capacitors?  Should I place C92 close to pin A5?  On the EVM I can't tell exactly which pin capacitors are placed close to because I don't have SW that will read the *SchDoc or *OutJob files included in the layout design files zip on the TI website.  I've also tried looking at the "TIDM845.PDF" file, but it's impossible to search for the capacitor I'm looking for and have it be highlighted so I can see its pin location on the AWR1843AOP (See below).  I can't see or identify the AWR1843AOP pins because NOT all pins show on this view and if you search for a capacitor reference designator, it doesn't highlight the part in this view.  All of this to say, is there an existing guide that instructs what pin to place the decoupling capacitor close to in a customer layout design?  I'm attempting to closely match the EVM as much as possible and I think getting decoupling capacitor placement right is important.

  • Decoupling capacitor placement is very important indeed. However, I dont believe there is a detailed guide on the exact placement of the capacitors. We recommend placing it as close to the pin as possible. And as stated in the Errata, we recommend trying to acouid components to the North and South of the device. 

    Hope this helps,

    E. Shareef

  • Unfortunately, this does not help because I am looking for an understanding of which pin to place the capacitor close to for scenarios where there is one part and multiple pins to cover.  The input you provided above is an example:  You stated to place C91 of the EVM schematic close to pin C1.  The schematic says that C91 covers the "VNWA SUPPLY".  The VNWA supply pins are V14, V7, and C1.  How do I know it's supposed to be placed next to C1 vs. V14 and V7???  The same could be said for C92 which says to cover "SRAM SUPPLY" or pins V12, V6, and A5.  How do I know which of these pins to place C92 next to and not next to the others?  There are more instances with similar decisions to be made.  Do you have any feedback that can help me in this effort?

  • I don't believe we have such priority pin selection guide. Let me discuss this with our design team and get back to you.

    Thanks, 

    E. Shareef 

  • Okay. Thank you for the update.  I'm trying to finish up our prototype PCB layout design in the next week so if you could please get back to me within a week, that would be greatly appreciated.  Is this time frame feasible on your end?  Obviously, the sooner the better.

  • Yes that should be feasible. 

    -E. Shareef 

  • Okay.  Thanks, E. Shareef!  I'll be awaiting reply.

  • Hello,

    Our reference EVM design is what we can provide for the placement of the decoupling capacitors, as this changes from device to device. 

    Thanks,

    E. Shareef

  • E. Shareef,  Thank you, but I was hoping for a reference that is viewable using standard available software (SW).  As I've said in the thread above, the EVM layout design is NOT something that I'm able to view (*.SchDoc or *.OutJob files) w/ any type of standard available SW.  Can you tell me what free available SW I can use to view these files?  These are not Gerber files (*.art).  The available PDF of the layout does NOT allow me to search to find capacitors because the size of the PCB is too small on the PDF:  When you search a component, the PDF SW zooms way back out and it's impossible to see where the component is located in relation to the AWR1843AOP pin it's expected to be placed near to in the schematic drawing.  Therefore, the formats that you have available currently are not something that can be viewed by a user w/ standard available SW that I'm aware of.  Will you please provide what you suggest to use to view the *.SchDoc and *.OutJob files???  In searching, these are Altium files and the company I work for does NOT have an Altium license to view these files.  Is there a free viewer that would work?

  • Altium Designer should have a free version on which you can view the .PrjPcb Altium files. 

    Hoipe this helps,

    E. Shareef