BQ24735: Power Path management?

Hello Giuseppe,

This part is capable of providing power to your system above the battery voltage in the event that the battery is deeply discharged.

It also incorporates a boost-mode controller which boosts the battery voltage to the SYS voltage to prevent the adapter from collapsing. This is current based from a comparison between the current limit set by the FAST_DPM threshold that uses the ILIM parameter and the current measured by ACN & ACP.

I'm sorry but this is not completely clear to me. I need a charger that "insulates" the battery whenever the adapter is connected. Is this the case?

Many thanks

Giuseppe

Hello Giuseppe,

I am not sure what you mean by the term insulate. What this charger does is that when an adapter is connected it will use the external half-bridge to buck the voltage of the adapter down to the necessary battery charging voltage. This charging case does not have the battery directly connected to the adapter input.

The boost case only matters if you expect your system load current to be greater than the current the adapter can provide.

The BATFET is used when the adapter is disconnected and you want a lower impedance path from the battery to the system which will improve efficiency.

Let me know if that cleared anything up or if you have more questions.

Thanks for the answer, Ryan.

Anyway I think I could explain better what I meant. Let me use TI words to suggest you what I'm looking for:

"When the qualified adapter is present, the system is directly connected to the adapter. Otherwise, the system is connected to the battery. In addition, the power path prevents battery from boosting back to the input." 

Giuseppe

Hello Guiseppe,

The FETs Q1 & Q2 are configured to prevent back-boost to the input. This FET configuration can stop current flowing in either direction. This combined with the reverse input protection circuit shown in the application circuit and the adapter input should be protected from having energy from the battery being boosted back to the adapter.

The other way to ensure that there is no boosting of the battery voltage back to the input is to size the boot strap capacitor properly. I would recommend following the recommendations given in the datasheet.

Hello Ryan,

thank you for the answer. Do you mean that this protection, also, enables this capability? "When the qualified adapter is present, the system is directly connected to the adapter. Otherwise, the system is connected to the battery"

Hello Ryan,

So I understand that the system is powered from the AC adaptator if it is present, or from the battery if the adaptator is not present but the battery is present. Is that right ?

But if there is no adaptator and the battery is present (power from the battery to the system) and then we plug the adaptator, the power will come from the adaptator and the battery will be change from dischare to charge without any trouble on the line of the system ?

Thanks,

Alex

Hello Alex,

When the battery is the only thing present power will be drawn from it as long as it is in a safe operating range. Whenever an adapter is connected it will draw from the adapter instead

There maybe some voltage variation at the time of the source transition but it should not interrupt the downstream system