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Topic starter
2024-09-09 1:31 pm
Hello,
I just joined the forum/workshop, so if you're interested, feel free to check out my "introduce yourself" topic.
but let's get back to the topic:
Some while ago I've built a KNX device, and I always need to connect a few pins when I want to flash new firmware to the RP2040. Currently, I'm working on a new design and want to integrate a USB-C port directly onto the PCB – this would make development and flashing more convenient.
Now I have the following problem: 99.999% of the time, the device is powered by the KNX bus. The NCN5130
provides both 5V and 3.3V. My concern is that with the presence of a USB port and the need to regulate the 5V USB voltage to 3.3V, the LDO regulator could also be activated during KNX operation, even though 5V and 3.3V are already available. This seems inefficient to me. Are my concerns valid? Should I rather place a diode/MOSFET between the USB port (VBUS/VSYS) and the 5V supply?
Attached is a screenshot with a MOSFET (Q2) already planned in.
Please note that the KNX bus and USB will never be connected at the same time. This is also the case with certified KNX devices.
Best regards,
Sebastian
2024-09-09 3:31 pm
@exotelis
never be connected at the same time.
Famous last words. A Schottky diode might be in order.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.
Topic starter
2024-09-09 3:58 pm
@exotelis
never be connected at the same time.
Famous last words. A Schottky diode might be in order.
Hehe 🙂 At least, nothing bad would happen.
A Schottky diode was my plan b? But in general I'm not completely wrong with my thoughts, am I?
Thanks for your feedback
2024-09-09 8:20 pm
@exotelis You aren't wrong, but what is the cost of the inefficiency? Sometimes the cost of 'fixing' it exceeds the benefit. I would not be concerned, but I am not that well versed in stuff that came after vacuum tubes.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.
2024-09-09 9:09 pm
Place a P-channel MOSFET or Schottky diode between the USB VBUS and the 5V supply. The MOSFET gate can be controlled by the presence of the USB VBUS signal.
2024-09-10 1:37 pm
@aliarifat Remember to use the Reply link so the person you are talking to is notified.
Yes, that is exactly what Bill (dronebot-workshop) said in his introductory PICO video/article.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.
Topic starter
2024-09-10 1:55 pm
@zander It seems I missed that video. I'll have to look it up, unless you have it ready at hand?
I'll probably order a prototype board and test both cases. I decided to use a Schottky diode (MBR120VLSFT1G), which should do the job.
Thank you all for your feedback. Your help is much appreciated 🙂
2024-09-10 11:03 pm
@exotelis Here is the article https://dronebotworkshop.com/pico-uno/#Pico_Power_Pins
Videos are good to catch your interest, but learning comes from reading and re-reading the article.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.