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Question on USB OTG on imx6 rex

Johnnyjax , 06-05-2020, 09:10 AM
I'm designing an imx6 board and i'm not designing a 5v regulator on the board but i want to add a USB OTG on the board. Is it compulsory that i use a 5v regulator on my board? i saw that in a video where you tested the IMX6 rex module without the baseboard, you said you attached a USB cable to the imx6 module but the imx6 rex module didnt have a 5v supply. I also saw this in the hardware development guide for imx6 processors where they said "if your system is a USB device, then USB_H1_VBUS may be a no connect". Does that mean i can leave USB_h1_VBUS floating and the 5v Pin from the otg cable floating too? I also have another question about all the "Not Fitted" components on the module and baseboard. You wrote some notes on some of the components regarding when they should be placed and when they shouldn't but you didnt for some. My question is, can the board work without all the "Not fitted" components. When you manufactured the module and baseboard, did you send a note to the pcb assembly house telling them not to place the "Not fitted" components or were some placed. Because i'm thinking of removing all the "Not Fitted" components from mine but i don't know if the board will still work without them. Thanks
robertferanec , 06-06-2020, 03:24 AM
- Yes, you need 5V for CPU USB - it is compulsory.
- Variant Prototype was manufactured - so unfitted components in Variant "Prototype" should not be fitted during manufacturing.
Johnnyjax , 06-06-2020, 03:32 AM
Thanks. Does the 5v supply from the OTG cable count as a 5v source? Can I connect it directly to USB_H1_VBUS and not add a regulator on board.
robertferanec , 06-08-2020, 04:11 AM
Does the 5v supply from the OTG cable count as a 5v source? Can I connect it directly to USB_H1_VBUS and not add a regulator on board.
- I would say, that theoretically yes ... but I am not sure what are the conditions of the 5V (e.g. when exactly it has to be connected to the pins, what will happen if it is not, how stable it has to be, etc ....). Some of our iMX6 boards can be powered from USB, but in that case USB is the main power source, I am not sure how your board would be connected (e.g. if you are using USB as the power source or if you are using also something else to power your board.).

You can have a look at our OpenRex and download its schematic (that board can be powered from USB):
Completely Open Source. Based on Freescale i.MX6 CPU. Arduino & Raspberry Pi like headers. All documents are free for download, including Schematic and PCB.
Johnnyjax , 06-08-2020, 06:09 AM
Thanks. I took a look at the openrex schematic and saw that there was a really cool pmic chip you used- MMPF0100NPAEP. My question now is how is the power sequencing done on a chip like this. I saw in the datasheet that it's a non-programmed chip. Does that mean all I have to do is assemble the board and itll just work if everything is connected properly or do I still have to worry about programming it.
Johnnyjax , 06-08-2020, 06:17 AM
And I just finished the advanced pcb layout course and although you explained how fly-by topology is routed, I'll prefer to route in t-branch topology since that was the one you went into details with. Can the 4gb ddr3 on the openrex be easily routed in t branch like it was covered in the course or should I use fly-by? And I'd also like to know why you used fly-by instead of t-branch like you did on the imx6rex module
Johnnyjax , 06-09-2020, 09:10 AM
I finally saw a post you wrote on the imx6rex.com about the PMIC chip but i dont have access to the evaluation board for programming the PMIC chips. I'm just a student and doing this project to learn and making my own IMX6 custom board is already too expensive enough so i'll like to avoid expenses wherever i can. Can i instead work with the ISL6236AIRZ chip in the imx6rex module and baseboard design instead though i'll still have to figure out how to do the power sequencing but it'll be a lot cheaper than having to buy the evaluation board for the PMIC. Will everything i need for figuring our the power sequencing of the ISL6236AIRZ chip be in it's datasheet? And i'm thinking of maybe using the IMX6rex module and baseboard design as my reference design instead and leaving just a few peripherals i need and making it into one board. What do you think of that? Will i still be able to follow your linux course with a board like that when i'm done. Thanks.
robertferanec , 06-12-2020, 12:25 AM
@Johnnyjax if this is your very first complex project, I would recommend you to stick as closely as possible to the reference board ... if you are not experienced enough and if you do too many changes you may end up with a non working board. Of course you can change power supplies and of course you can change memory topology .... but you need to know what you are doing. But, based on the questions, you do not know what to do and how to do it - so I am not sure if making too many changes is the best idea.

What is your priority? Would you like to design a board were you practice and everything is working when finished, you will get confidence and you can use the board to show it to you possible employer or you would like to design something what you do not know exactly how to design, it is a great and super exciting challenge and if working then it will be fantastic achievement, but you are going into a very high risk, that the board is not going to work?

People will look if what you design is working ... they will not care much about what power supply or memory topology you used. If you have decided to design that board then paying a little bit more extra for working board is much more valuable than trying to save and end up with a board which may not work.

Do not take me wrong, but if designing complex boards would be so simple that anyone after watching a video could do that, we would have world full of great engineers. Designing boards is also about experience and skills ... and trying to design a complex board with a little experience is risky. Therefore it is safer to stay as close as possible with to what works. But ... that is just my opinion, maybe I am too careful
Johnnyjax , 06-12-2020, 01:27 AM
Oh... wow. Thanks
Johnnyjax , 06-12-2020, 05:22 AM
I've decided that I'll stick to your advise. I'll use the openrex design as a reference design and remove the peripherals I dont need and try not to change too many things. I'ts been my dream for years to be able to design a board like this and I'm ready to do anything so I'll look for the money. Thanks for your advise. I really appreciate your help and your response. It means so much to me.
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