[MinnowBoard] TurboT DualE board power by LSE header

Krau, Michael P michael.p.krau at intel.com
Thu Apr 12 23:10:06 UTC 2018


Hello Alex,

Your message reminded me of some discussions from back in the design phase of the original MinnowBoard Max.

Remembering that the 5 volts on the LSE was originally intended to provide power to external devices connected to the LSE, I was struck by other memories around that discussion.

The original MinnowBoard MAX basically ran power supply through the board, and limited expansion to ~3amp load (as mention before).

The MinnowBoard Max Turbot supplies +PS_5VSB to the LSE so that the LSE device would not be constrained by the regulation on the board, but could draw from the external power supply with minimum of circuitry (getting a bigger “wall-wart” to feed it).  The LSE device could regulate or adapt that 5 volt supply as necessary.

Since 3 volts was derived on the board, the LSE can only have the +3VSB signal (no external source).

In your use case, the concern would be having enough copper to carry the current from the LSE connector into the rest of the Turbot.  I think the original amperage allocation for the LSE (go out from the MinnowBoard MAX) was ~1 amp…  So 1 amp coming in, should not present a problem.

One thought, if you are not averse to making small modifications to the MinnowBoard Turbot itself, you could “blue wire” a secondary conductor from the LSE pin directly to another point on +PS_5VSB.  This would shunt some of the amperage away from the identified ‘thin spot’ to the rest of the board.    Though this is rather kludge solution, and just a thought.

Sincerely,



Michael Krau

While I am an Intel employee, I do not represent Intel and am not authorized to speak for Intel.

From: Alex Bakhtin [mailto:alex.bakhtin at gmail.com]
Sent: Thursday, April 12, 2018 2:55 PM
To: Krau, Michael P <michael.p.krau at intel.com>; Van Der Pol, MarkX <markx.van.der.pol at intel.com>
Cc: MinnowBoard Community Email List <elinux-minnowboard at lists.elinux.org>
Subject: Re: [MinnowBoard] TurboT DualE board power by LSE header

Mark, Michael,
    Thank you for your reply. I agree that the trace width between LSE header and Q103 could be a problem. And actually it is. There is one place with trace width approx 0.68 mm. I don't really know if there is 0.5 oz or 1 oz copper on L06. I think that this is ok for 1Amp on 0.5 oz because the rest of the trace width is about 1.4 mm.

[изображение.png]
From this board we need CPU, 2xGigE, RAM. mSATA for booting and probably USB for a flash drive.
To test the reliability - I ran dual cpuburn (burnK6 x 2 for 2 cores) for about 8 hours - and everything was fine. Unfortunatelly we don't have a thermal imager to check the PCB temperature at this point.

RIght now I'm not sure that this is a good idea to power this board by the LSE header. But I really don't have any other ideas.
Michael. Also today we accidentally applied the +12V on PS_5VSB on LSE header on one board:-( I'm pretty sure that U35 was failed. We'll replace it (spare NCT3012S would be delivered by our supplier at the end of next week) and check - if this was the only failed part - we are lucky:-)

чт, 12 апр. 2018 г. в 22:31, Krau, Michael P <michael.p.krau at intel.com<mailto:michael.p.krau at intel.com>>:
One historical piece of information:  The Original (non-Turbot) MinnowBoard MAX had a different implementation, where the LSE Header was not populate with the +PS_5VSB but with the (post regulator) 5VSB trace.   This ties back to Mark’s trace comments, as the +P5_5VSB traces should be more robust than the 5VSB, as the 3 volt rail is drawn from the +PS_5VSB.  In fact, I would doubt this solution would work on the non-Turbot MinnowBoard MAX, as the 3 volt rail would not be powered if the only source of power were 5 volts on the LSE.

During the board design, the 3 Amp rule was discussed, but I can’t remember if 3 Amps was the target (meaning there should be some additional margin) or the upper limit (including the margin).

I would like to think that the Turbot design change (5VSB to +PS_5VSB on the LSE) was done to accommodate projects like yours, where the LSE can be used as an alternate power supply source for the platform.  In which case they would have kept 3 AMPs as the standard…  However, since the 5 volt rail does not go through the on board regulator, it also means that the system is not protected by the 5 volt regulator.  Accidentally putting 12 volts on the LSE 5volt pin could fry the board (instead of simply frying the regulator), and providing more amperage than the traces of the board can handle could have detrimental impact on the board under high load.

The question that comes up is how much current does your application draw when fully operational?  If the draw is low enough, then it should be within the design rules applied.

The photo does look great!

Michael Krau

While I am an Intel employee, I do not represent Intel and am not authorized to speak for Intel.

From: elinux-MinnowBoard [mailto:elinux-minnowboard-bounces at lists.elinux.org<mailto:elinux-minnowboard-bounces at lists.elinux.org>] On Behalf Of Van Der Pol, MarkX
Sent: Thursday, April 12, 2018 11:23 AM
To: alex.bakhtin at gmail.com<mailto:alex.bakhtin at gmail.com>
Cc: MinnowBoard Community Email List <elinux-minnowboard at lists.elinux.org<mailto:elinux-minnowboard at lists.elinux.org>>

Subject: Re: [MinnowBoard] TurboT DualE board power by LSE header

It is under investigation – while the circuit works, there is a concern if the PCB traces from the LSE header to the regulator are sized big enough to handle the current demands of the board and modules. It is supposed to be able to handle 3Amp, and I don’t know if that was actually implemented, and if that design rule was enforced into the board layout. And I don’t know what safety margin exists on the design rule, if it was applied.

So – as you discovered, it works fine. And, until the analysis is done on the trace current capacity, we don’t know if it is reliable. There is risk of it failing under load.

Thanks for sharing the update and photo! It looks great!

|\/|ark.

Mark van der Pol
Firmware Engineer,
Open Hardware Team,
Open Source Technology Center
Intel
Markx.van.der.pol at intel.com<mailto:Markx.van.der.pol at intel.com>

The MinnowBoard.org Foundation: a US-based non-profit providing education and promotion of the design and use of open-source software and hardware in embedded computing on Intel® Architecture.



From: elinux-MinnowBoard [mailto:elinux-minnowboard-bounces at lists.elinux.org] On Behalf Of Alex Bakhtin
Sent: Thursday, April 12, 2018 12:38 AM
To: elinux-minnowboard at lists.elinux.org<mailto:elinux-minnowboard at lists.elinux.org>
Subject: Re: [MinnowBoard] TurboT DualE board power by LSE header

Nobody sent a reply.
We made some testing and designed a simple PSU to check this idea. Everything is working fine.


[image001.jpg]
вс, 1 апр. 2018 г. в 1:31, Alex Bakhtin <alex.bakhtin at gmail.com<mailto:alex.bakhtin at gmail.com>>:
Hello.
    Is it possible to power the TurboT Dual-Ethernet - Dual Core board from LSE header?
    Right not we are testing how TurboT fits out project. TurboT could be one of the core components, but the whole device should be dual-powered (220V AC and 10-36VDC). From my point of view - this is a good idea to desing a PCB on which we would install our PSU, and also provide a mounting space for TurboT - holes and connection to the LSE header (I think we would also use one uart from LSE header).
    I checked the turbot schematics and I see that DC_IN_1 (power supply connector) is filtered by an LC filter, connected to protection curcuit and after that is connected to +PS_5VSB.
    +PS_5VSB is connected to pin 3 of LSE header and supply 5V power to the rest of the board. So, according to turbot schematics - we can supply +5V to the PS_5VSB directly and everything should be fine.
    In the turbot gerber files I can see that this pin is connected to polygon on Layer 06, and it seems that this polygon is directly connected to Q103 and FB1->U13 (3V power supply).
    Is it ok to supply 5VDC it from LSE header? Thank you.
Alex Bakhtin
--

Alex Bakhtin
--

Alex Bakhtin
--

Alex Bakhtin
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