Allow me to say that I’m quite new to PCB design and circuits. Please be precise and elaborative when answering as I imagine this is a typical beginners question.
I was wondering how to connect a USB type C connector to the FT232RL (USB to Serial converter). Let me use the arduino nano schematic as an example.
In here let’s zoom in on the USB module in the top-right corner. At the border of section B7 and C7 on the schematic. The Arduino Nano uses a USB Mini B female connector.
USB Mini B Pin 1 connected to GND
USB Mini B Pin 2 not connected
USB Mini B Pin 3 connected to Pin 15 of the FT232RL
USB Mini B Pin 4 connected to Pin 16 of the FT232RL
USB Mini B Pin 5 connected to a fuse the MFFSMF050
Now let’s look at the USB type C connector and a table from the data sheet of this connector:
Can I just take the type C connector and connect:
USB Type C Pin A1, A12, B12, B1 and the Shell to GND
USB Type C Pin A6 and B6 to Pin 15 of the FT232RL
USB Type C Pin A7 and B7 to Pin 16 of the FT232RL
USB Type C Pin A4, A9, B4 and B9 to the fuse (MFFSMF050) seen in the Arduino schematic.
Can I just make these connections mentioned above? Or do I have to place diodes to prevent current from flowing back to the connector, what would be good specifications for this diode if I have to add them? I have not worked with reversible connectors before.
While I’m at it, I’d like to ask about the fuse in the Arduino schematic the MFFSMF050. I couldn’t find much about it on the internet and I figured it could be one of these gold Arduino fuses that we can find on the Arduino Uno as well. Is anyone able to tell me what kind of voltage and current limits would be suitable for the fuse placed here?
You need 5.1 k resistors (Rd in the USB C spec) to ground from each CC pin to indicate a device is connected and enable VBUS in a USB C peripheral. Raspberry Pi 4 got this wrong connecting CC1 and CC2 together and using a single resistor.
As shown, it’s equivalent of connecting your mini B through a USB C to A dongle. Host or a high power device is more complex.
The connector used in the attachment is a USB 2.0 only reduced pin count part, so you have more VBUS and ground pins.
Excellent! Thank you very much for your quick reply and example schematic. A picture is worth a thousand words!
Yes, I am aware this will use the USB 2.0 standard and I am not looking for more than just to able to use a USB type C cable.
Could you please take 2 seconds to review my schematic below? I added a 01x05 header and my aim is to be able to interchange the USB mini B and USB type C connector. Is that correct?
I stumbled across this data sheet as well.
If I assume the Arduino Schematic contains a typo should be “MF-MSMF050” instead of the on the schematic specified “MFFSMF050”. Then yes, it would be the one below. However I lack the knowledge to judge if these specifications are appropriate here. What do you think?
The schematic has a symbol for a zener diode. So it must be this one: MBR0520LT1, which is suitable, exactly like the schematic states. This is not a fuse, you have drawn there.
Correct, my schematic has the zener diode. However in the official Arduino Nano schematic referenced in my first post: https://content.arduino.cc/assets/NanoV3.3_sch.pdf there is a fuse marked as MFFSMF050 before this zener diode. Marked with the blue rectangle here:
Except that the official Arduino Nano schematic doesn’t have a Zener diode on it at all. I think that @mifi mistook your D3 as a Schottky diode and you didn’t correct him. FWIW, I just checked the part number that you used, MBR0520LT, and it is a Schottky diode as you intended.
If you look up the part number from the Arduino schematic, SS1P3L, you will find that it is also a Schottky diode. A quick check of specs, it appears that the one you chose is only 15 cents less expensive at Digikey ($0.30 vs $0.45 of the Arduino part), but can only handle half the current (0.5A vs. the 1.0A of the Arduino part), and can handle 2/3 of the reverse voltage (20V vs the 30V of the Arduino part). Is that $0.15USD really worth it for a lower safety margin, and theoretically lower lifetime (the closer you run a part to it’s maximum specs, the more you shorten its expected lifetime). But, I may have missed something. I didn’t compare specs that carefully.
That diode performs an OR-ing function with the two possible power sources. The forward voltage drop with a typical load current may be a parameter of special interest, and affect the choice of one diode over another.
The MBR0520LT was simply already in the KiCad symbol library and someone else used it. The SS1P3L was not. Enough reason for me to be somewhat certain it would do it’s job properly here. I turned out to be not that easy. I since have made a footprint and symbol for the SS1P3L myself and replaced the other diode with this one. Thanks for pointing this out SembazuruCDE!
This is also the source that made me question the fuse. This schematic and BOM do not include the fuse and I was considering to leave it out but wanted to ask for some advice on a forum before I committed to this
Thanks Dale for clarifying the diode’s function here!
Could you perhaps elaborate on the mechanism of the diodes action is? How is this diode select between USB power source (?) and an other power source connected to the VIN pin of the Arduino (?). I’m not sure these are the two options this diode is performing its OR-ing function, but this seemed the most logical and intuitive answer to me. The Wikipedia page on this topic is rather lacking. Maybe rather than explaining this just to me the world could become a little smarter by giving this page some love.
I am planning to just use the USB power as input for this device. Does this mean I can drop this part of the original Arduino Nano schematic in my design?
Well, usually there is a diode in series with each of the two power sources and the source with the more positive value supplies current to the load, because its diode is forward biased and the other source’s diode is reverse biased.
This particular application needs a little more thought and study to give a thorough explanation. My boss is expecting me to do something profitable this afternoon, but here are two links off the top of a Google search which may help answer your question.
Don’t you need some kind of protection between the USB connector and the FT232RL chip? There are integrated devices especially designed for USB protection. Obviously, as the speeds (edge rates, really) get faster, protection becomes a more difficult affair because of the extra parasitics it introduces. Remember, it is not the bit rates that define signal integrity requirements, but the edge rates (although faster bit rates demand faster edge rates of the pulses). You can do your own search on the web, but here are some examples (the last one is best):
Well I’m not sure. The device will only be powered off of PC or laptop usb ports. I imagine computers have some protection on their USB ports as well. So not by external power supplies or anything like that. I guess double protection is not a bad idea either. Assuming the “MFFSMF050” was a typo in the official Arduino Nano schematic I could use the “MFMSMF050”. I am not sure if the official circuit references this part though (15V and 100A seems a bit high for me?). If it does, I will just use the MFMSMF050 and call it a day. Unless you guys have better advice and can explain why I should do differently.
Also yes, I am well aware my project will only utilise USB 2.0 speeds/features. I just wanted to be able to use a USB type C connector and cable as they are becoming more common than USB mini B from my observation. The reason why you see a 01x05 connector just behind the connector in my schematic is with the idea that if I ever want the USB mini B for any reason I can just swap the connector. My schematic linked here does not have the fuse (yet?).
Furthermore the USB port will be the only power input to this circuit. That’s also why I wonder If I should use the Schottky diode performing:
Also I wonder if this part I copied from the official Arduino Nano Schematic is relevant to me at all in my situation because it seems to just be a linear voltage regulator regulating voltage from 6-12V to 5V and if I can simply leave it out. Because I will use 5V from USB. I have no and will never have a power source connected to the VIN pin of the Arduino Nano on this circuit.
There are several valid reasons to include this if it isn’t too painful on your part. One is you may wish to expand on this design in the future. Another is that this is a learning experience for you and going through the effort to include it is useful. Always that gap between theory and practice. Still, your project and your decision to make depending on your parameters. This post isn’t to try and convince you that you are wrong or beat up on you, just to get you to think a little ahead of this project.
