The reset circuit caused some trouble in M1 rc3, due to the high capacitance of the diodes and their reverse leakage current, which makes the real-life performance of the diodes very different from that of ideal diodes.
An alternative solution would be to use logic gates. They provide a very clean separation between their input and their output. The 74AUP family can operate at voltages as low as 0.8 V, so the gates should already be fully operational before most of the system has even quite realized that it has power. The following schematics show three circuit variants: http://downloads.qi-hardware.com/people/werner/m1/rst/rst.ps Upper left and lower left differ in the use of chips in SC-70 vs. uQFN packages. The one on the right uses a more analog approach, allowing the use of the same chip for both functions. Sebastien prefers the fully digital solution, i.e., the left-hand side. As a reminder, this is the current circuit in M1 rc3 (after rework): http://en.qi-hardware.com/wiki/File:M1_rc3_hw_fix2.png Regarding sourcing, the 74AUP1G07 and 74AUP1G08 are available from TI and NXP: http://focus.ti.com/lit/ds/symlink/sn74aup1g07.pdf http://www.nxp.com/documents/data_sheet/74AUP1G07.pdf http://focus.ti.com/lit/ds/symlink/sn74aup1g08.pdf http://www.nxp.com/documents/data_sheet/74AUP1G08.pdf They come in a number of different packages. The following charts compare the TI and NXP packages and group those with compatible footprints together: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/pkgology/1g-dyadic http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/pkgology/1g-monadic In order to avoid unpleasant surprises during sourcing, it's desirable to use a package that is available from more than one manufacturer. Furthermore, the chips in question should be stocked by major distributors. (Lead time from the manufacturers would be painfully long 2-3 months.) The following charts show the availability as of last weekend: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/sourcery/74AUP1G07 http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/sourcery/74AUP1G08 We can see that the DCK/GW and the DSF/GF packages have good to reasonable availability. Unless space becomes a concern, the SC-70 packages (DCK/GW) would be the preferred choice, due to better availabilty and being easier to solder and rework. The KiCad schematics, along with a BOOKSHELF file, are here: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/m1rc3/gates/ - Werner _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode Twitter: www.twitter.com/milkymistvj Ideas? http://milkymist.uservoice.com
