This is always not clear to me so here I am again.
The device that I am building has 2 sub-devices.
1 needs 3.3v and the other needs 6.0v
So, do I merely sum them together = 9.3v, add in a bit of overhead, and look around for a 10v LIPO ?
Or can I use a pair of DC-DC buck converters, and use them to bring a 7.3v LIPO down to the required voltages ?
Thanks
I would say it depends on how much power each device uses and how much space you have for the battery / batteries.
If the device uses little (or less) current at 6v, it may be more efficient to use a step-up (boost) regulator to boost a lower voltage (ex ~3.3v to 4v) up to 6v
For example, you may design your product with 3 AA or AAA batteries (3 rechargeable would give you ~ 3x1.1..1.3v = 3.3v-3.6v, so a small LDO would give you 3.2v..3.3v with minimal loss. Or, you may use a single 18650 lipo with 3.6v..4.2v with a small buck regulator to get 3.3v
Then separately boost for 6v or whatever you need.
Also consider conveniences like being able to charge the battery with a small 5v usb charger (or power the product while charger is plugged in and charging the battery)- a charger IC for a single lithium battery is less than 50 cents and works with 5v, something for higher voltage batteries is more complex.