USB 2.0 hub chip

Jul 31, 2009 8 Replies
T

I want to modify a laptop to fit an internal USB flash drive. While there's USB available inside all the ports are used, so I need to insert a two port hub in between one of them so I can break out another connector.



The trouble is space is /extremely/ tight. That means everything will have to be uncased, hardwired in, with no USB connectors. And the amount of area I have to fit in a PCB isn't large (constrained in thickness and in area by various pillars etc)



I've been looking around for a USB hub I can abuse in this way, but the problem is that the type A sockets used are hugely bigger than the chip used so there's no reason for the board layout to be compact. I found something like this:

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The sockets are mounted on a bar which could easily be trimmed off, and I'd hope the area under the label containing the chips would be small enough. But according to the comments this hub gets hot, which is always a concern in a laptop.



So I wondered if it was easier to make it myself with a chip I could get data for, rather than wandering around the shops peering through the packaging trying to work out which chipset is used. Only I can't seem to find anyone (I'm in the UK) selling USB 2.0 hub chips. Plenty of 1.1 though. Digikey has some 2.0, but the delivery is very expensive.



I realise layout of a USB 2.0 board is a bit more tricky than 1.1 due to the higher speeds. But I'm only using it for very short distances, and every piece of Chinese tat seems to manage it with the cheapest construction available. And in theory I'd only need a chip with power, ground, 2 crystal pins, 2 USB pins in and N*2 USB pins out, not a TQFP64 or something.



So is there a sensible source of USB 2.0 hub chips in 1-off quantities that won't cost me a fortune? For example, someone like Maxim with a samples programme (Maxim don't make hubs) or someone who ships small orders? Or is my best bet still to wander around the shops looking at translucent hubs until I find one with a suitable chip and desolder it?



Thanks Theo


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L

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That's rather large.

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looks like it might be a drop-in.

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P

If USB A sockets are large to you and space constraints what are you going to do about preferable USB designs that have large cap on 5V to each USB port.

Well I bought a small batch of NXP1520 four port USB hub chips in UK, if stuck I can probably sort out a small quantity for you.

What I configured the four port to actually be a three port hub on a stripboard and schmart board lash up, worked perfectly well with 5m cables.

see

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Also has a USB device chip talking to a PLD and then other logic not shown.

Paul Carpenter | paul@pcserviceselectronics.co.uk PC Services Timing Diagram Font GNU H8 - compiler & Renesas H8/H8S/H8 Tiny For those web sites you hate
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T

All this is internal to the laptop, and both devices are ones I fix (original onboard webcam/bluetooth and USB flash stick I choose). All being low power devices there shouldn't be a problem with the maximum power draw. Is there much need for extra capacitance given the 5V switching PSU is only an inch or few away? I can see a need if you attach a 10m USB cable to the hub due to the extra resistance, but here it's minimal. I can always remove/downscale any caps that are already fitted.

Thanks. I might try first finding a readymade hub to butcher as it saves having to wire up my board.

That's very useful to know... just the sort of thing I'm likely to do.

Thanks Theo

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T

That looks useful (but in the US). Perhaps I should look at two-port hubs.

Theo

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D

the guys at the EEE PC group have been doing this since the 7" netbook came out in late 2007.

Have a hunt around at:

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and I'm sure you will find many examples, complete with pictures.

Cheers Don...

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P

The cap is normally after any power switching/limit and is to deal with the device connected. If you have a fixed INTERNAL device, you don't need the USB connector, just wire and no capacitor.

No such thing as a 10m USB cable 5m is the MAX length of USB as longer means the 5V will not be 5V enough to power devices.

...

Paul Carpenter | paul@pcserviceselectronics.co.uk PC Services Timing Diagram Font GNU H8 - compiler & Renesas H8/H8S/H8 Tiny For those web sites you hate
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T

Ah, good idea! I don't have an eeePC so I was looking on the forum for my laptop - should have thought about the eee forum too!

Theo

>
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N

The cable length limit is primarily due to the maximum propagation delay (30ns total, of which 26ns is allocated to the cable). If it wasn't for that, a 10m cable would just need thicker power lines.

At the speed of light in vacuum, 26ns is 7.8m, so a 10m USB cable[*] would require a fundamental scientific breakthrough.

[*] As opposed to a 10m cable with USB connectors on the end, which isn't quite the same thing.
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