RPi4 foil path current carrying capacity.

[LTolledo]

This question is directed to RPi engineers (and/or those who have first-hand knowledge on the matter)

on the RPi4B:
1. is the GPIO header pin 2 (and 4) electrically connected (with nothing in between, like controller chips, etc) with the USB port's VCC? (Yes/No)
2. what is the maximum current carrying capacity (as designed) of that foil path from GPIO header pin 2/4 to the USB port's VCC? (_____mA)

for #1, am not able to determine that on the schematic diagram posted here:
https://www.raspberrypi.org/documentati ... /README.md

hoping to get an enlightening response....

thanks as always

[hippy]

1. is the GPIO header pin 2 (and 4) electrically connected (with nothing in between, like controller chips, etc) with the USB port's VCC? (Yes/No)

No.

The 5V on pins 2 and 4 of the header connects directly to the USB-C power input socket pins. But there is an AP2552 USB current limiting chip between 5V and VBUS which goes to the USB 2.0 and USB 3.0 sockets.

The Pi 4B USB monitoring circuit was revealed by James Adam (RPT) and can be found at -

viewtopic.php?t=247353#p1513413

[LTolledo]

thanks hippy for the link:

so the simple answers are:
1. No
2. n/A

I'll take these as the final answer

[hippy]

Cross-edited so moved my added note here as it might be useful in your case - Though it seems you did see my answer - I'll leave it as is !

It has been confirmed by other forum members that one can bypass the AP2552 and connect 5V from the header pins directly to the USB socket pins. That will carry as much current as the wire, connectors and solder joints are rated for.

One of course loses any over-current protection on USB.

[LTolledo]

yes I did see your cross-edited text... quite interesting fact.

if the AP2552 is bypassed, backfeed protection is compromised as well.... correct?
nah, don't want to do that on the board itself

there are "better solutions" to ramp up USB current
or "better device" choices to deal with the USB current limit....

[hippy]

if the AP2552 is bypassed, backfeed protection is compromised as well.... correct?

That's true - Allowing back-feed powering is why I have done it on some of my Pi !

Not such a great idea though if one is connecting powered USB devices without cutting the power wire in their USB cables.

[TheFireman]

The 5V on pins 2 and 4 of the header connects directly to the USB-C power input socket pins.

so, does this mean that connecting 5V 4A power supply to pin 2 is functionally equivalent to connecting the power to the USBC?

I am setting up a Pi4 in a dedicated function ( picture frame) and this would make some of the wiring easier for me.


BTW is the same true for the older Pi's MicroUSB power connector?

I have some two dozen fairly high-quality 5V-4A wall warts I picked up during a shop closure.
Some have tinned ends, others barrel connectors.
Connecting to pin 2 is easy... FOR ME
Adding USB connectors, not so much.. FOR ME
YMMV

Thank you

[davidcoton]

so, does this mean that connecting 5V 4A power supply to pin 2 is functionally equivalent to connecting the power to the USBC?

Yes. You will do just as much damage when you get the polarity wrong on either input. It's just harder to get it wrong on pre-made USB-C cables.
I recommend putting a suitable fuse (or polyfuse) in the supply, so when the polarity is wrong the fuse goes before the TVS protection diode. This applies to ANY Pi supplied via the GPIO header, and Pi0 and Pi4 versions with home-made USB cable supplies.

BTW is the same true for the older Pi's MicroUSB power connector?

No. The Pi 1,2,3 models have an on-board polyfuse for the USB power connector, which is bypassed when supplying power via the GPIO header.

[hippy]

The 5V on pins 2 and 4 of the header connects directly to the USB-C power input socket pins.

so, does this mean that connecting 5V 4A power supply to pin 2 is functionally equivalent to connecting the power to the USBC?

Correct.

BTW is the same true for the older Pi's MicroUSB power connector?

Generally yes.

On PI with micro-USB, except for the Zero and Zero W, there are a variety of components between the micro-USB connector and the 5V rail. You lose the functionality of those components when connecting direct to the GPIO header.

Power input connections, and what the variety of components are, is in all the published schematics.