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I'm studying some schematics about Google Coral Dev Board, and I have found this:

enter image description here

Where VBUS_1 comes from USB-C OTG connector and VBUS_VIN comes from USB-C Power only connector. What is the resistors 0R target? I understand that diodes block return way current, but that resistors let current flows.

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    \$\begingroup\$ DNP probably stands for "do not populate", so only the bottom 0R resistor will be placed. It's a typical pattern to choose between a direct connection or the diode depending on the assembly. \$\endgroup\$
    – Arsenal
    Commented Apr 7, 2022 at 10:07
  • \$\begingroup\$ Does this answer your question? What is the usage of Zero Ohm & MiliOhm Resistor? \$\endgroup\$
    – Arsenal
    Commented Apr 7, 2022 at 10:10
  • \$\begingroup\$ @Arsenal it is not exactly my question. My question is more related with the configuration diode + resistor than the 0 ohm resistor. I don't understand in which case both components are placed, or if this configuration makes sense or not. \$\endgroup\$
    – Juanma
    Commented Apr 7, 2022 at 12:54

2 Answers 2

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The DNP probably stands for do not populate, so there might be different variants around during assembly - or there were during development until it was settled to just the one variant being sold now.

Based on this schematic I can think of up to five configurations making sense (without knowing exactly what USB_VIN and USB_VBUS are):

Populate:

  1. Only R26 -> device is powered from USB_VIN
  2. Only R176 -> device is powered from USB_VBUS
  3. Only D12 -> device is powered from USB_VIN (minus diode drop), VIN is protected from getting reverse currents
  4. Only D5 -> device is powered from USB_VBUS (minus diode drop) VBUS is protected from getting reverse currents
  5. D5 and D12 -> device is powered either from VIN or VBUS (minus diode drop) depending on which is higher ("diode or" of two power supplies) both are protected from reverse currents

Populating both resistors makes no sense, as you might run into shorting VBUS to VIN. Which could destroy one or both supplies.

Populating a 0 ohm resistor and a diode in parallel makes no sense as the diode wouldn't be active.

Note: when the resistor wouldn't be 0 R, the analysis would change - so a resistor parallel to a diode might have some value in some other circuit.

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  • \$\begingroup\$ Thank you so much! Now all is clear. \$\endgroup\$
    – Juanma
    Commented Apr 7, 2022 at 13:41
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If you were to look at an actual circuit board you would find that not all 4 of these components are placed.

Note the "DNP" designator on all 4 of these parts. This stands for "Do not place" or "Do not populate" and indicates OPTIONAL assembly.

So when assembling this product there are more than one assemblies that are specified depending on the product variation.

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  • \$\begingroup\$ But, it doesn't make sense if both components (diode + resistor) are assemblied, right? \$\endgroup\$
    – Juanma
    Commented Apr 7, 2022 at 12:53
  • \$\begingroup\$ You are correct. There is no point in paralleling a diode and a 0 ohm resistor. \$\endgroup\$
    – jwh20
    Commented Apr 7, 2022 at 14:46

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