TPS61130: Combination of USB and battery power

Hi Alexis,

Thank you for reaching out on E2E.

May I know your application output voltage and maximum load current requirement?

Hi Zack,

We have a 3V battery (in reality should be around 2.6V average for our drawn current) and USB as sources. The load needs 3.3V and 50mA maximum current (but an average value would be around 35mA).

Thus, I have computed for this case that the inductor L1 should be around 80 to 100uH considering maximum load current and considering 40% current ripple and the switching frequency between 400kHz and 600kHz. Thus I plan using a flying capacitor of 2.2uF or 2.7uF (with low ESR). Does this make sense?

By the way, the datasheet gives some values for the output capacitors when combining the LDO and SEPIC outputs, but it does not provide information to tune them (as it does for other configurations). Do you have some recommendations to scale them to my output voltage and maximum load current (and possibly tune them during testing)?

Thanks

Hi Alexis,

Thanks for the information.

TPS61130 should have enough capability for 50mA maximum current. But it's hard to give priority to USB.

How about using a buck-boost converter TPS63XXX and using below configuration? When USB exists, the upper diode conducts and works as supply of the buck-boost converter, when USB doesn't exists, the lower diode conducts and works as the buck-boost converter power supply.

Hi Zack, 
Indeed that sounds like a good idea. TPS63011 would be the only one available (I want minimum input voltage below 2.3V at least).
The needed capacitors and inductors seem to be smaller and easier to choose.
Thanks