I am starting to design a custom carrier board based on the Ixora reference design.
The Ixora Carrier Board v1.3 schematic has a note, added since v1.2:
The current USB power supply circuit is not ideal.
If you are planning to implement it in your custom carrier board, please check the relevant reference schematic contained in the USB section of the related Carrier Board Design Guide.
The PDF version of this schematic has a date of 5/7/2023.
The latest version of the Apalis Carrier Board Design Guide linked from the Ixora Carrier Board page is v1.14, released on 09/13/2022, approximately 8 months before the schematic was updated. The revision history specifically calls out updates to the USB reference schematics.
The power IC used in the Type-A reference design in this document is 0.5A instead of 1.0A and is at end of life. It also uses the older ESD protection before v1.3 of the schematic was “updated to use the same device used on other interfaces and therefore reduce the BOM” (from the Revision History page).
The Ixora Carrier Board v1.3 schematic uses the same power IC as the v1.2 schematic, which according to the PDF was released on 08/08/2019.
So there are a few questions:
- Why does the v1.3 schematic contain the same power supply as v1.2 if the Carrier Board Design Guide was different when it was released? It supplies 2 USB ports vs 1 in the reference design, so it makes sense that it needs 1.0A instead of the 0.5A, but why does the note then say to refer to the reference design that won’t work?
- What is the actual concern with the existing circuit as people have been using it for years? This doesn’t seem like the kind of warning that would be thrown on there without reason, but it also doesn’t seem important enough that anyone has updated the Carrier Board Design Guide.
- Is there a newer reference design that should be followed? I have been accessing the documentation via Ixora Carrier Board | Toradex Developer Center
Thank you
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Greetings,
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The Ixora Carrier Board v1.3 schematic retains the same power supply as v1.2 due to the specific requirements of the Ixora design, which includes supporting two USB ports that necessitate a higher current supply (1.0A) compared to the single port design in the Carrier Board Design Guide. The note in the schematic suggests referring to the Carrier Board Design Guide for updated USB power supply circuit designs, acknowledging that while the guide’s reference design might not directly apply due to its lower current specification (0.5A), it contains valuable design principles and newer components that could be beneficial. The intention is likely to encourage designers to consider these newer design elements while adapting the circuit to meet the higher current requirements of their specific application.
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The concern with the existing USB power supply circuit may relate to several factors, including the end-of-life status of the power IC used, potential limitations in supporting newer USB specifications, or improvements in ESD protection. While the circuit has been functional and widely used, the note implies that there are recognized areas for improvement, particularly for new designs that might benefit from more modern components and design practices. The inclusion of such a note suggests a proactive approach to design optimization, encouraging designers to seek the most current and effective solutions.
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As for a newer reference design, the situation you’ve described indicates that the most recent publicly available documentation might not fully reflect the latest design recommendations for the USB power supply circuit, especially considering the date discrepancies you’ve noted. In such cases, it’s advisable to consult the latest Carrier Board Design Guides and schematics available directly from Toradex, as these documents are periodically updated to incorporate new design standards, components, and best practices. While the specific documentation you’ve accessed might not show a newer design, Toradex continuously updates their resources to aid developers in creating robust and future-proof designs.
For your design based on the Ixora Carrier Board v1.3, it would be prudent to integrate the general design principles and newer components recommended in the Carrier Board Design Guide, adjusting the design to meet the specific current requirements of your application. This approach ensures that your custom carrier board benefits from the latest design improvements while accommodating the necessary power supply specifications.
Best regards,
Toradex AI Assistant
Please, also check if these links can help you solve your problem:
Iris Carrier Board | Toradex Developer Center.
Thank you, AI. But the parts used in the Carrier Board Design Guide are end of life so that doesn’t make sense. Perhaps a human can weigh in?
The position of the bulk capacitors is a problem for the OTG port. It needs to be moved to the other side of the power switch. The problem is that if the caps are on the connector side, they are also active in case the OTG is used as a client. However, in client mode, one cannot have more than 10uF load when plugging in the connector. Otherwise, the VBUS might drop too low and violates the USB specifications
Thank you! We won’t be using OTG so it won’t be a problem for our application.
