Maximum current available on the 3.3V pins of the Technic Hub/Boost Hub/City Hub?

[arohrbacher]

As the title says, does anybody know how much current one can draw from the 3.3V supply (pin 3/GND and pin 4/VCC, see The Powered Up connector ) on the PUP sockets of the various LEGO Powered Up hubs? The reason I am asking is that I am working with home-made PUP sensors/displays/etc (see DIY-PU-Sensor ) and want to avoid drawing too much current from the 3.3V line (and possibly destroying something in the hub).
I would imagine that the LEGO 3x3 LED matrix draws quite a bit of current when fully on, but it might be that this item is powered from the "motor PWM" pins 1 and 2 - I can't say for sure as I don't own one of these LEGO matrices...
I tried to find a schematic of the LEGO hubs, but didn't find anything that would tell me more. Even a partial schematic of how the 3.3V are generated from the batteries would help...

Thanks in advance!

[dlech]

LEGO didn't release any schematics for the Powered Up hubs, so we don't know what kind of regulators they have and what the current limit is. But we do know that the sensors with lights do use battery power on pin 1 or pin 2 like you suspect.

Maybe you could identify the regulator from a picture of the electronics, like the one here.

[arohrbacher]

Thanks for the reply.

I knew about your photos of the Lego Hub innards, but I can't really make out what regulator Lego uses...

In the meantime I did some tests and it seems that a 40 mA draw is still OK. I ran an RP2040-Matrix board (an RP2040 chip with 25 Neopixels) off of the 3.3V Technic Hub pins and told the board (via Pybricks, using an appropriate firmware on the RP2040) to light up all 25 LEDs white at ~12% intensity (which is bright enough): I measured a total current of 40 mA and I didn't see any negative effects. I didn't dare to increase the LED brightness and thus increase the current draw, though - don't want to fry my Technic Hub...

[dlech]

Thanks for the follow up. I happened to have a Technic hub with the cover off, so I had a look and the chip is marked:

QUJ
TI 88F
S57E

Which matches https://www.ti.com/product/TPS63060. This can put out 2A at 5V although it recommends to limit it to 1A. So you can probably make your LEDs just a little brighter. 😄

[arohrbacher]

Great, thanks for checking this! Good to know we can draw up to 1A from the 3.3V rail (at least for the Technic Hub and the City Hub: your photo here also shows a chip marked with "QUJ") - this opens up quite some possibilities...