This has been asked and answered many times, but my specific question is not in the list of results when I search.

I have a nominal 2.6A supply here, and it remains stable at 5V up to exactly this amp load with no voltage drop. It’s quality. So I would just like to know if I need to do some resistor magic/short-circuit on the TX/RX lines for it to work perfectly with my pi3.

I’ve observed on most quality 5V supplies that RX/TX are shorted, and I am aware of apple’s weird voltage divider circus on their iPhone/iPad PSUs - but this is a Pi - does it even pay attention to RX/TX signal lines?

My expected max load is 1.5-2A, not more. I’ll pull an extra 5V rail from this PSU for something else nearby.

Let me know if I need to clarify.

Note: I’ve used a 2.1A iPad charger up to now, and it does not work well at all. Even when I observe a load of only 1.3A, there are not-enough-power indicators when I attach 50mA USB peripherals. A standard off the shelf charger at 2A has no issues... But I need the extra 5V rail for something else nearby.

TL;DR: I am connecting 5V/GND to a male microUSB breakout board, and need to know if using resistors or shorting the data lines (the aforementioned RX/TX) will in any way affect the Pi’s operation. If so, how?

Update: The PSU wasn’t the issue; I was using too thin, too long a cable. At the Pi I measured 5.10V when it was turned off, but ~4.85V when on and loaded. So I should read 5.25V at the Pi when it’s off:/

  • Could you explain what the RX/TX lines are? I can make no sense of the question. I can't see any relevance to the Raspberry Pi.
    – joan
    Mar 25, 2018 at 15:04
  • Receive and transmission lines in a standard USB1.1/2 cable. I’m connecting the 5V/GND to the 5V/GND pins on a little male microUSB breakout board, and am curious to know if the RX/TX pins are relevant. See electronics.stackexchange.com/questions/123172/… . I would have asked on EE.SE, but they’d obviously say this question belongs here.
    – user2497
    Mar 25, 2018 at 15:08
  • For posterity: A value of 0-200 ohms between the data pins on USB1/USB2 informs a device that this power source conforms to the DCP section of USB Battery Charging Specification, i.e. a source capable of providing <= 1.5A.
    – user2497
    Mar 25, 2018 at 17:47

1 Answer 1


The Pi's microUSB power socket is only connected to pins 1 (5V) and 5 (ground). Pins 2, 3, and 4 are not connected.

Schematics at https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/README.md


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