paulpthcom

Well going to try these, hopefully they work and pretty sure I can solder in the 1210 case in the 0805 pads without problems. If that fails I'll either try the Murata or just try a different chip altogether. Thanks for the help, I'm pretty confused on this one too.

And there we go, just tried a 4.7uH PTH from my parts drawer and it starts up properly with the load as low as 1.0V. So seems to me that even the 600mA 4.7uH SMDs just wasn't enough. Time to go back to digikey and see if I can find something that can handle even more current, though I'm pretty sure that means going up in package size.

The board is super tiny, everything is close to everything else. Just tried out an experiment, I rigger up a 22uH PTH and everything is working much better. As long as the startup voltage is >= 2.0 it output 3.3 with the load. Without the load it can startup at ~1.1V. So either my other inductors were too small or their current rating was too low. Will try some more PTHs to see what happens...

Soldered up another one of the boards and still seeing the same weird behavior. One thing I noticed is if I start without the resistor load and then add it, things seem to behave as expected. Really odd behavior all around. I've included the super simple schematic I had built, maybe someone can spot something stupid I'm missing, but otherwise I'm out of ideas.

I'm using this but when I bought it was labeled Mastech. Works well enough and was cheap, only complain is I wish the fan was quieter.

They are 10uF ceramics, just a 1-2K resistor between output and ground. I don't think there's any shorts anywhere but I think I'm going to solder up another board just to make sure none of the parts have released their magic smoke without me realizing it.

OK so now with the new 4.7uH inductor I get more weird behavior. From 1.0-1.5 V in I get 3.3 V out, from 1.7-2.7 V in I get around 3.0-2.7 V out. The new 10uH inductor just doesn't work at all, the output voltage stays in the mOHM range and the current just gets higher and higher as I crank up the input voltage (up to 500 mA). I'm confused.

Well live and learn and resolder. Maybe I'll get lucky and digikey will deliver the goodies tomorrow so I can try again. I'd like to say I'll read the datasheet more carefully next time but I'd probably be lying. ;-)

I ordered up some 4.7uH and 10uH inductors from digikey with beefier max and saturation current ratings. Hopefully that's enough to get this behaving properly. Thanks for pointing out the importance of high current rating on these.

I switched over to a different 10uH inductor and found the following behavior. If I ramp up my power supply from a low voltage the output voltage stays at around 1.5Vs and starts using more and more current, up to 300mA. Once I hit ~2.1V the output jumps to 3.3V and the current usage drops to < 10mA. I can then ramp down my input voltage to .8V and the output stays at 3.3v. I'm sure there's some logical explanation for this, will read over the datasheet to see what's what, but hey at least it all is somewhat working.

400+ mA saturation current, not "max DC current"? I wish the datasheet had been a bit more explicit about this... Got a link handy to the one you use?

I believe its http://www.yuden.co.jp/ut/product/category/inductor/CKS21254R7M-T.pdf but not 100% sure, says 130mA as the rated current. I also have tried a 10uH http://www.digikey.com/product-detail/en/MLZ2012N100L/445-6762-2-ND/2523500, saturation current 110mA with the same results. Source power supply is just one of those Chinese linear mode bench supplies.

I must be missing something really basic, but I have a TPS61221 hooked up with a reference schematic, 10uF Input and Output caps and a 4.7uH inductor. With no load I get a 3.3 output voltage as expected. I hook up a simple 1k resistor load and the output voltage drops to ~2.2 volts. Anyone know what I'm doing wrong?

Tested out the PA+LNA module. Seems to work down to about 1.8-1.9 volts. In power down mode it + the 2452 I'm using consume about 1.6uA vs 0.9uA for the non PA+LNA module. Both of these are actually much better than I had expected. Not really sure how to go about getting a good measurement of peak transmit current, but setting my multimeter to store 1k readings and scrolling through them the max I saw was around 50mA. Still waiting to get a couple more sets so I can try both the RX and TX using one and see if it makes enough of a difference in my application to work.

So I'll start up by admitting this is horrible code, you probably shouldn't use it and it's just generally a bad idea, but someone might find it useful. I'm targeting a 2452 without hardware UART and wanted to be able to printf solely for debugging purposes. I know that there's at least one implementation that uses Timer A and T0.1 to implement a soft UART. That version is much more bullet proof and if you actually need to get every last byte you should use that, or better yet a chip with a hardware UART. That being said I only need this for debugging and can miss a character once in a whi