FEDEVEL
Platform forum

, 03-18-2024, 01:58 PM

Hello all, I have a question regarding differential pairs routing. Can I use vias in the layout of the traces?
What should I keep in mind while doing it?

A bit context,
I'm working on a board having
type C, USB Type A stacked, and ethernet signal lines.

Board is of 4 layers.

Thanks in advance!

QDrives , 03-18-2024, 03:52 PM

You can put vias in traces, but for the differential pair they both need to have them. Keep the length of each section as equal as possible (needed).
Do not forget the Gnd stiching via.

, 03-20-2024, 08:33 AM

Also, can I use the middle layers for signal routing? Given above conditions.

ashesh223 , 03-20-2024, 09:33 AM

I've done routing with vias and stitching as above. Can you please verify?

Robert Feranec , 03-20-2024, 01:32 PM

if I have space I place four of them with the diff vias between them, but for this usb I dont think it is super critical

, 03-20-2024, 02:24 PM

Thanks for the response @Robert Feranec
One more thing I would like to ask is, having this condition. Can we use the middle two layers for some signals routing like the GPIOs or PWM signals.

Sniper2 , 03-20-2024, 05:34 PM

4 ? how i cant imagine this?

Robert Feranec , 03-21-2024, 06:38 AM

it would be more like this .... but often just two vias are ok

Sniper2 , 03-21-2024, 06:54 PM

hmm i dont see much of a difference honestly

Robert Feranec , 03-22-2024, 06:13 AM

this may help, nice simulations to see the fields https://youtu.be/yQIBS5xwvVQ?si=2-JmxwXU_ME4EbyD

ashesh223 , 03-27-2024, 05:59 AM

Hi, can you do a quick review and tell me what corrections are required in this routing?

Context of the layout.
Type-A USB stacked, Ethernet and USB-type-C. are connected to Raspberry Pi CM04.
For Type-A USB stacked is connected with a USB 2.0 Hi-Speed Hub Controller.
USB 2.0 Hi-Speed Hub Controller and USB type-c are connected with FSUSB42MUX.
USB type C is also used for powering up the board.

QDrives , 03-27-2024, 03:29 PM

I would not route tracks underneath USB and ethernet connector on the top layer as often these connectors are metal and can cause a short.
In your last comment, can you also state which connector is which (ie. J6 is ethernet ...)

Robert Feranec , 03-28-2024, 07:40 AM

this doesn't look right ... may not be able to manufacture, looks too close. I am not sure where you are going to manufacture the PCB but very basic design rules can be found for example here: https://jlcpcb.com/capabilities/pcb-capabilities

QDrives , 03-28-2024, 04:01 PM

You may want to increase the track to hole clearance rule for that.

ashesh223 , 05-14-2024, 01:13 PM

Hey,
I have a confusion in the timer power design as shown in the picture.
I'm using the load switch TPS22950CDDCR

And we have 3 different loads
1. Raspberry Pi
2. SIM module
3. USB module ( IC + MUX + USB port stacked)

Also wanted to know, is it necessary to add the delay circuit in the power.

What could happen if we remove the timer circuit.

If you could guide me in this. Thanks in advance!

Robert Feranec , 05-14-2024, 05:42 PM

you can control power of the peripherals from RPI - e.g. you connect some RPI GPIO pins to the enable pin of power supplies. It is sometimes useful e.g. if you would like to save power by switching off some peripherals or if you would like to reset specific peripherals (e.g. if modem form some reson gets stuck). Just be sure these peripherals can be powered off when RPI is on, because sometimes there may be currents leaking through peripherals which are powered off and connected to chips that are powered on.