MEGAphone low-current DC:DC Converter Module

In the previous post, I set about designing and laying out the high-current (2A) DC:DC converter for the MEGAphone.  For draws of 10mA, that should still be 92% efficient across the plausible 2.6V to 3.6V battery voltage range.  That's probably good enough.

Of course when I started looking to see if there were any options for even better efficiency at lower current levels, I found this one:

https://www.ti.com/lit/ds/symlink/tps631000.pdf

It's possibly even more efficient over the whole current range:

 

But what's really interesting, is that it doesn't have a thermal pad underneath it -- i.e., this thing would be way easier to hand assemble -- especially given that it also requires fewer passives. That would also allow the module to be physically smaller. They even include a sample layout, which I was silently a bit annoyed that the other one didn't:

So all up, this looks like a good option to use instead of the other design, as even at the lowest battery voltage, it should still be able to deliver ~2A, but at higher battery voltages, it can even deliver 3A or more.  *sigh*

The question is whether it is worth designing a module around this right now or not.

I suspect the effort is better invested in creating another module instead... although hand-assembly is very attractive, as it would let me put off figuring out how to use the PCBWay assembly service for a bit longer.

Another option, though, is to use the same DC:DC converter that is on the MPPT module I've derived from this.  Having commonality of the part is attractive for reducing the unique part count that I will need to have on hand. Also, I can in principle just replicate the circuit and layout from that one, and know that it's already been tested.

That design uses a AP63203, which, unfortunately has a minimum input voltage of 3.8V, which is above the full level of our LiFePO4 single-cell battery. Bother! I'd even gone and adapted the MPPT module down to having just this module. Oh well. 

The TPS631000 looks like it will be what we will need to use. We'll also hook it up so that it can deliver either 1.8V or 3.3V, to cover the two most likely voltages we will need. I'll do this by again providing an extra resistor that goes parallel to the feedback voltage resistor ladder:

To select 1.8V output the 1V8 SEL line should be tied to VOUT (not GND, as that would _increase_ the output voltage!). To help avoid people making mistakes with this, I've added silkscreen instructions that they should be tied for 1.8V output.

Okay, so the repo wit this module is at https://github.com/gardners/megaphone-low-current-dc-dc-converter, because I started by using the MPPT project, even though now there is nothing in common with it.

I've also provided a MODE pin for pulling to GND if you have a load that is ~1mA or less, and really want to get an extra bit of efficiency. But 50% efficiency at 1mA still only means 1mA wasted, so we aren't going to bother using this in the MEGAphone. But the facility is there for those who might want it, if using this module in something else.

The module now looks like this:

So that's that one also schematic and PCB layout done, satisfying

Milestone 2.2.2 - Low-energy power-management module to minimise engery consumption of the device: Schematic

Milestone 2.2.3 - Low-energy power-management module to minimise engery consumption of the device:PCB Layout [sic]

I've already got a PCBWay order in progress, that is waiting for a 4-layer board to be fabricated, which will take 4 days more, so I can easily add this one onto the order, which I've done.