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Joined: Thu Oct 25, 2018 7:35 am

Adding power control to USB hub

Wed Oct 16, 2019 4:04 pm

Hi all,
I'm trying to add a software-controlled power switch to a USB hub I have. The hub uses the Terminus Tech FE1.1s USB hub chip which, according to the datasheet (linked below) has "Ganged Power Control" (which I found means that all ports share a single power switch). As far as I am able to understand the (rather cryptic) data sheet, the PWRJ output pin (pin 25) is used for controlling the power, and it works as a digital output pin, with low (<0.4V) indicating the power shall be connected, and high (2.4V) meaning that power should be cut.
I'm now trying to use that PWRJ output pin as a way to actually control the hub's downstream power from software. According to a blogpost I found (linked below), all that's needed is probably a transistor and a resistor on the downstream VBUS line.
The blog post is about a different hub chip that has individual output pins for all downstream ports, and these are called PPB(4:1).

However, I am a real noob at electronics and am now trying to figure out how the instructions from that blog post translate to my project (with a different hub chip). So, here are my questions, in the hope that someone with more experience in electronics is willing to help :D :)

1) Are the FE1.1s PWRJ pin’s characteristics equivalent to the PPB(4:1) pins on the NEC USB hub IC used in that blog?
The FE1.1s data sheet only says PWRJ is "Downstream Device Power Enable, active low, for Ganged Power Switching.", and that likely means it's a digital output, which are <0.4V low to 2.4V high. The NEC chip’s data sheet says the corresponding PPB pins are "5 V tolerant N-ch open drain" and low active. What does 5V tolerant mean for an output pin? If I read the datasheet correctly, I think the logic levels are the same (0.4/2.4V)?
2) Should the same circuit as in the blog post work for me as well?
3) How do I know what transistor and resistor to use? The blog post doesn’t include any specifics about that.

FE1.1s data sheet: https://cdn-shop.adafruit.com/product-f ... .+1.0).pdf
Blog post for NEC hub chip: https://befinitiv.wordpress.com/2014/02 ... usb-hub-2/
NEC hub chip datasheet: http://pdf.datasheetcatalog.com/datashe ... 276_DS.pdf

Any help is highly appreciated!

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