3
\$\begingroup\$

I am new and now I am trying to understand some basic schemes. My questions are:

  1. Do I understand correctly that the wave in the diagram stands for Ferrite band in this case rated at 100 Ω 100 MHz 4 A max?
  2. J17 is not used in production because is it labeled as "DNP" and probably it is evolved for prototype with external power source?
  3. Schottky diodes are used for voltage protection even if J17 is not involved? Scheme
\$\endgroup\$
2
  • 2
    \$\begingroup\$ You inserted a piece of what seems to be the schematics of Raspberry Pi, the part with the famous bug in it why they had to make another revision. I would not call it "some basic schematics", it isn't, it's a highly specialized circuit for a Type-C USB interface, which is not an easy feat. Proved by the error in there. Please provide proper attribution from where you got that piece of schematics. \$\endgroup\$
    – Justme
    Commented Jul 8 at 16:43
  • \$\begingroup\$ Actually its from a schematic of "Dual Gigabit Ethernet NICs CM4 Carrier Board for Raspberry Pi CM4", from seeduino link, my plan is to make more siple version of it, but firstly i need even to understand it. \$\endgroup\$
    – Noobie
    Commented Jul 8 at 19:45

3 Answers 3

Reset to default
6
\$\begingroup\$
  1. No and Yes.

You have circled both a fuse F1 and a ferrite bead FB16.

The wavy component is the fuse, rated 5A. The ring with wire through is the ferrite bead.

Ferrite beads are typically rate d at 100 MHz frequency, so it would be rated 100 ohm @ 100 MHz rated for 4A current. Now, what is missing is the resistance, i.e. how much the voltage drops based on current.

  1. Maybe, either for providing supply when USB not applied, or testing the supply when provided by USB. Your guess is as good as anyone's, but when I designed something with USB, I also had same arrangement for powering the boards to check if they are safe to plug into a PC that would program the boards.

  2. Yes, for protection, not because external supply connector, but simply because it's USB. It is a hot-plugged interface and there can be large voltage and current steps, when device is plugged in or unplugged, and how bad the surges are depend on cable and which end of the cable you either plug or disconnect. The cable has inductance and you need to handle that.

Also, the way you drew the schematics is wrong and will not work, it is not done as per USB specs. It looks like the same issue made famous by Raspberry Pi. You simply cannot tie CC pins together and expect it to work, except in a couple of scenarios but not all.

Edit: Oh it actually is the RPi schematics. You should have mentioned it.

\$\endgroup\$
9
  • 1
    \$\begingroup\$ 1. The resistance is right there on the schematic. 100R is the code for 100 ohms. In a number scheme that I think originated in Europe, the letter that conveys the multiplier also is used as the decimal point. This greatly reduces the number of errors caused by dirty copiers, bad faxes, etc. Example - 2700 ohms = 2K7. 1K 5% = 1K0. 1K 1% = 1K00. The parametric frequency is not shown on the schematic. \$\endgroup\$
    – AnalogKid
    Commented Jul 8 at 18:12
  • \$\begingroup\$ @AnalogKid you would not pass 4A through 100 ohm resistance. I will heavily argue that my interpretation it being a 100 ohms at 100 MHz still holds as that is the most common way of putting labels on schematics, and the DCR would be separately put and it would be in milliohms or tens of milliohms for lower amperage models. \$\endgroup\$
    – Justme
    Commented Jul 8 at 18:21
  • \$\begingroup\$ So as you mention it will not work? Its from schematics of "Dual Gigabit Ethernet NICs CM4 Carrier Board for Raspberry Pi CM4", from seeduino link \$\endgroup\$
    – Noobie
    Commented Jul 8 at 19:50
  • 2
    \$\begingroup\$ @Noobie They are a company, making a lot of stuff quickly and cheaply for hobbyists. It does not mean they have a process with no errors in the design, especially if they copied the same legendary RPi4 error. Basically it does not work with e-marked cables. It's been all over the net why it always does not work. For example in Lifehacker, Hackaday, Ars Technica, PCMag, Tom's Hardware and Arrow have articles on it. \$\endgroup\$
    – Justme
    Commented Jul 8 at 20:18
  • 1
    \$\begingroup\$ @MarkMorganLloyd Yes, exactly, whatever EDA package that is, it seems to be the standard symbol for a ferrite bead in it. \$\endgroup\$
    – Justme
    Commented Jul 9 at 13:30
3
\$\begingroup\$

  1. The wave part is the symbol for a fuse. It is rated for 5 A and is in a 1210 surface-mount package. To the right of it is a ferrite bead.

  2. DNP stands for Do Not Populate. It might be something left over from a prototype phase of the design.

  3. Those are zener diodes, not Schottkys. It looks like dual-redundant 5 V transient clamps.

\$\endgroup\$
2
\$\begingroup\$

1- "The wave" is F1, it is a fuse, and it's rated at 5A.

2- Yes, it's for use with an external power source.

3- D44 is not a shcottky diode; it's a TVS diode (not zener), and its use is ESD protection.

\$\endgroup\$
1
  • \$\begingroup\$ The TVS is not for ESD protection. The U24 is a fast ESD protection device. The TVS is for protecting against voltage surges from cable plug/unplug events. \$\endgroup\$
    – Justme
    Commented Jul 8 at 19:55

Not the answer you're looking for? Browse other questions tagged or ask your own question.