BQ25504: Adding USB charging to BQ25504 solar energy harvesting

Pascal Roobrouck

Part Number: BQ25504

Tool/software:

Hi, I'm designing a wireless sensor and it runs on a LiFePO4 battery and can be charged from USB using the MCP73123 as LiFePO4 charger delivering energy into VBAT

Now I'd like to add a Solar Cell as an optional energy source. It looks like the BQ25504 has all the features I need.

But can it be used in parallel with the MCP73123 ?

Here is a quick schematic of what I'd like to do

Thank you for your advice.

7 months ago

0 Michael Emanuel35 7 months ago

TI__Mastermind 40635 points

Hello,

We are observing Presidents Day and will get back to you tomorrow.

Regards,

Mike Emanuel

0 Pascal Roobrouck 7 months ago

Prodigy 10 points

In the mean time I've figured out I don't need the OK_Hyst and OK_Prog signals, so this simplifies the design. New schematic attached below.

0 Pascal Roobrouck 7 months ago

Prodigy 10 points

I can always put a PFET in the output of each charger, and let the MCU decide which one to use, but if it can work 'automatic' (charging the battery from whichever charger is active) I would prefer that, as it simplifies the design.

0 Michael Emanuel35 7 months ago in reply to Pascal Roobrouck

TI__Mastermind 40635 points

Hello,

What solar panel is being used to charge the battery? Keep in mind the BQ25504 is a boost charger.

In general you would need to make sure both chargers are not charging at the same time, please design the isolation according to your application. I cannot comment on the MCP73123 as it is not a TI part.

Regards,

Mike Emanuel

0 Pascal Roobrouck 7 months ago in reply to Michael Emanuel35

Prodigy 10 points

I am evaluating several 1 or 2 cell panels. Voc is 2.4V, the LiFePO4 has a minimum of 2.8V so this should work.

I understand you are not commenting on non-TI parts.

Anyway, I've decided to give it a try and will built a prototype : I assume a charger is adapting its output to the battery storage, and is simply pumping charge into it. So two chargers in parallel should work.

If needed I can always add PFETs to isolate them from each other, but I don't thinks it's needed.

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BQ25504: Adding USB charging to BQ25504 solar energy harvesting