BQ25756: Add power supply from battery

Hi Nishie,

For the BQ25756, there is no power path. That means that the system is directly connected to the battery. Your diagram is slightly incorrect in the sense that the power is flowing from the battery to the system through the IC.

What would happen in this instance is the USB would supply 5 W to the BQ25756 and the BQ25756 would output the 5W (minus some losses) to the system and battery combined at the same node. If the system power requirement is under 5 W, the system would be powered by the charger and the rest of the power would be used to charge the battery. If the system power requirement is above 5W, the charger would provide 5 W to the system. Since there are no protections between the battery and the system in this instance, the battery would provide as much power as the system requires up to the power the battery can provide until the battery cannot provide any more power.

If you would like protections between the battery and the system like your diagram is showing, you would need a different charger IC that has NVDC power path and a feature we call "Supplement Mode."

Best,

Michael

Hi Michael-san,

Thank you for your support.

Michael Bradbourne said:

If the system power requirement is above 5W, the charger would provide 5 W to the system. Since there are no protections between the battery and the system in this instance, the battery would provide as much power as the system requires up to the power the battery can provide until the battery cannot provide any more power.

Regarding your explanation, am I correct in understanding that if the battery power does not meet the power required by the system, the system will not be able to run?

Michael Bradbourne said:

If you would like protections between the battery and the system like your diagram is showing, you would need a different charger IC that has NVDC power path and a feature we call "Supplement Mode."

Could you please let me know if there is a product that has the protection functions and meets the configuration I originally described?

Best Regards,

Nishie

Hi Nishie-san,

Yuta Nishie said:

Regarding your explanation, am I correct in understanding that if the battery power does not meet the power required by the system, the system will not be able to run?

Correct. If the system demands more output than the charger IC plus the battery can provide, the system will not have enough power provided to perform its tasks.

Yuta Nishie said:

Could you please let me know if there is a product that has the protection functions and meets the configuration I originally described?

We should have products that can do this, but I will need to know what your input voltage/current requirements you have and what battery voltage/charge current requirements you have.

Best,

Michael

Hi Michael-san,

I have confirmed the input voltage/current and battery voltage/current with the customer. But I have not received a response from the customer yet. I will contact you when I get the information.

Best Regards,

Nishie