XS1-A8-64 Stick Project

XCore Project reviews, ideas, videos and proposals.
ale500
Respected Member
Posts: 259
Joined: Thu Sep 16, 2010 9:15 am

XS1-A8-64 Stick Project

Postby ale500 » Sat Oct 17, 2015 3:31 pm

I'd like to make a couple Sticks based on the XS1-A8-64, the BGA96 device. A couple questions come to mind... which coils do I need ? I know there are "power" coils but which one ?
I have also an "old" XTAG board and I ask myself if that one can program these newer devices, any thoughts ?
User avatar
mon2
XCore Legend
Posts: 1679
Joined: Thu Jun 10, 2010 11:43 am

Postby mon2 » Sat Oct 17, 2015 10:04 pm

https://www.xmos.com/support/silicon/da ... nent=16648

search for the keyword "inductor" which is the power coil you are referencing. Section 15, page 25 of this datasheet lists the criteria for the proper selection of a suitable inductor. The criteria is to use a 4.7 uH value inductor with ideally a DCR value of 70 milliohms or lower for best efficiency of the switching power supplies.

The CBC2518T4R7M from Taiyo Yuden is very low cost (under $0.20 USD) but is with a relatively high DCR value and is a pseudo-shielded part but will work. The higher cost units will run around $ 1.50 USD or lower but will be magnetically shielded and will be a much lower DCR value so higher efficiency on the local switching power supply which means lower heat when or if the XMOS CPU is being used to the max and respectively can support higher currents with the selected inductor. If attempting to use in a design for resale then EMI (emissions) must be considered so you do want to use shielded inductors.

Perhaps an overkill selection but Wurth 744043004 is a good choice for a shielded, low DCR, high current inductor for the task. Taiyo Yuden offers many similar choices as well at varying costs.

http://www.digikey.com/product-detail/e ... ND/1008236

http://www.digikey.com/product-detail/e ... ND/1639160

A recommendation is to use the Wurth 744043004 footprint on your PCB design and then you can consider to use either the Wurth 744043004 or the Taiyo Yuden CBC2518T4R7M at assembly time. We have done this with many of our designs with success and will often toggle to use either device based on inventory levels.

How many of these widgets (prototypes) are you planning to build ? Sometimes the vendors will sample you the parts to encourage you (the engineer) to spec in the component for future business considerations.
ale500
Respected Member
Posts: 259
Joined: Thu Sep 16, 2010 9:15 am

Postby ale500 » Sun Oct 18, 2015 1:56 pm

Thanks for the information. I seem to have missed the exact section I was looking for....
I want to build just a few, start with 2 because I'll build them per hand.
ale500
Respected Member
Posts: 259
Joined: Thu Sep 16, 2010 9:15 am

Postby ale500 » Mon Oct 19, 2015 8:46 am

I was thinking on doing a prototype it like this. Of course I'd like a 40 DIP Stick... maybe the second round :).
The board is 5x5 cm, two layers.
You do not have the required permissions to view the files attached to this post.
User avatar
mon2
XCore Legend
Posts: 1679
Joined: Thu Jun 10, 2010 11:43 am

Postby mon2 » Tue Oct 20, 2015 8:04 pm

Looks good but a few minor comments:

1) From the datasheet, RST_N net should provide a pull-up to VDDIO. See section M.2. The chip appears to have an internal pull-up but consider to apply an external pull-up that can remain not stuffed it is not required. Best to cover all bases.

2) Consider to use a different footprint for the 24 mhz crystal. Appears you are using the HC-49S which is a gull-wing landing pattern. In the past, we had issues in shipping our products (PC host adapters) where the same footprint crystal were bumped off the PCB. A nightmare and expensive repair to bring back to the factory at our expense. Options are to consider a through hole version of the same (more structural strength in case the crystal is hit). Better yet, there are now plenty of 5x7, 3.2x2.5 and 2.5x2.0 (due to cell phone markets appear to be the lowest cost at this time of writing). You will have to decide on the most suitable choice based on your comfort of soldering. Also, source the best PPM rated device - 30ppm or lower are quite common and fair in costing.

3) Although not mandatory, consider 4L pcb vs. 2L. The 4L pcb will lower noise (EMI) emissions from this design. The premium for a 4L design is not so much over that for a 2L. There are many fairly low cost bare PCB prototype shops in Asia you can use.

4) Consider to use non-polarized bulk caps for the design. Appears that the 47 uf is polarized (tantalum ?). Samsung is a great vendor for ceramic caps (X7R or X5R dielectrics). Ceramics will last longer and have a lower ESR value. Tantalums are nasty when they die and they will someday and tank the design in the process.

5) You could dial down the bulk capacitance on the 3V3 rail which appears to be around 150 uf. The reason is to prevent in rush currents which can surface with too much onboard capacitance. Suggest to use 47 uf in a single location or better to use multiple 22uf across the board. On the topic of bulk capacitance, bear mind that with ceramic caps which are of low ESR values then the external power supply regulator should also be friendly with ceramic caps. If using a filtered power supply source then no issue but if using an external regulator, please review the component specs. Most LDO regulators are now ceramic (low ESR) friendly. Otherwise you can face ringing issues with the power line.

See here for more details:
http://www.ti.com/lit/an/slva115/slva115.pdf

6) Nice to have a LED to denote that the module is being powered. Perhaps another LED to just flash via a port pin to demonstrate the board is functional.

7) Here is a design from XMOS using a 40 pin DIP footprint but is based on a different CPU:

https://www.xcore.com/forum/viewtopic.php?f=7&t=1224

We have also designed something similar but is buried in the pile of open designs looking for closure. If there is an interest, we can certainly morph the assorted XMOS IPs we have tooled up for to release as a public design. Let us know of your feedback. Have fun !

Who is online

Users browsing this forum: No registered users and 1 guest