-
Torex it is
12/13/2016 at 03:33 • 0 commentsThe test boards came back today. It turns out that the Torex chip and the latest TI contender (the TPS61097A) are pin compatible, and I just misread the Torex datasheet. So one of the boards was a waste, but the other was able to test both.
The TPS61097A wasn't a lot better than any of the other TI hysteretic chips, but the Torex was. It wasn't as good as the NCP, but it will do. With the bench supply (1.8v) running the calibrate sketch, it draws around 40-45 µA so far as I can tell. When you look at the current on the scope, what you see are big spikes spaced around 4 ms apart, with mostly noise between them. The output voltage has about 20 mV of sawtooth in it that has a period consistent with that. For this application, that much ripple is acceptable, as long as it's consistent.
The price is a little higher than the NCP, but not critically. What worries me is that while DigiKey and Mouser both stock the part, their supply looks rather constrained to me.
-
More boost converters to try
12/08/2016 at 05:44 • 0 commentsI think maybe I've figured out what the issue is with the boost converters.
Both the TPS61221 and TLV61225 are hysteretic topologies. The NCP1402 was a PFM controller.
I've put in two more prototype design boards, one for the TPS61097A (also from TI), and one for the Torex XC9140C331MR-G. It's the latter one that gives me some hope - the datasheet specifically describes it as a PFM controller.
I have only read a little bit of the datasheet, but I am buoyed by the fact that the Torex and On Semi parts both claim to work the same way.
The Q:250 price at DigiKey is, unfortunately, 19¢ more, and it appears as though the supply is a bit on the constrained side. But in any event, the next step is to test it out. Boards and parts should be here soon.
-
The next contestant
12/04/2016 at 02:26 • 0 commentsThe next boost converter contestant will be the Torex XC9140C331MR-G. It requires a new board, so that'll take a week and a half. Le sigh.
-
TPS61221 not much better
12/03/2016 at 22:05 • 0 commentsWell, I guess the search for an alternative power supply continues. The TPS61221 samples arrived, and they're a little better than the TLV61225, but not much. It still draws over twice as much as the NCP1402 under test conditions.
The NCP1402 circuit had inductors that were 10 times the value of the TPS/TLV recommendations (47 µH instead of 4.7 µH - with 2x22µF output filter caps). I'm almost ready to try putting one of those in just to see what happens (not hoping for much, unfortunately).
-
Maker problems
12/03/2016 at 18:57 • 1 commentThe pile is growing.
-
Well, that went poorly
12/03/2016 at 03:44 • 0 commentsThe first prototype boards came back with the new layout for the TLV61225 boost converter.
With a bench supply, the old NCP1402 based boards took 30 µA. Under the same circumstances, the TLV61225 based board takes 80 µA. That's no good.
The good news is that the TPS61221 is pin-compatible with the TLV61225, so I'll give that a try. I'll be satisfied if the draw is under 50 µA even if it's not quite all the way down to 30 µA.
-
New power supply test boards
11/26/2016 at 01:23 • 0 commentsThe first boards came back with the new power supply based on the TLV61225. I haven't extensively tested the current draw, but the voltage, noise and ripple seem perfectly acceptable. The first boards I ordered had a couple errors on them, so I'm ordering a follow-on batch to correct them.
I am continuing to design standalone boards, but I'm unlikely to order another manufactured batch of them, as demand is quite low compared to the complete movements, and I have a ton of them still in stock.
-
New power supply
11/12/2016 at 23:55 • 0 commentsWell, the NCP1402 has been discontinued by On Semi. That's kind of a huge bummer, as it worked really well, and the design of the Crazy Clock had reached a more or less steady state.
Unfortunately, it's sort of hard to pick boost converters for this application. The best I could find is the TI TLV61225. On the plus side, an external Schottky diode is not required. It just requires an inductor and input and output caps. Fortunately or unfortunately, it comes in an SC-70 package. That makes it tiny and fiddly to work with, but the price is reasonably comparable.
I've ordered some boards to try with the new design. I've got plenty of inventory of the current design, so there's at least no big urgency.
-
Square inch contest
11/24/2015 at 19:26 • 0 commentsFor those who've come here from the entries in the Square Inch contest, make sure you consider the correct variant of the two that are mentioned here. The Q80 version of the board is too large, but the retrofit variant is 0.9" x 0.4". You can download the EAGLE files and confirm that yourself if you like.
-
EAGLE CAD files posted
09/20/2015 at 23:08 • 0 commentsI've posted links to the EAGLE CAD (v7) files for both the standalone and Quartex movement replacement board versions. With the BOM and the firmware repository, it means that anyone can make their own Crazy Clocks.