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BQ25606: Is it possible to charge a battery and power a load (Boost converter) simultaneously

Jaya krishna
Prodigy 70 points
Part Number: BQ25606

Hello TI Experts,

We are planning to use BQ25606 as part of the charging circuitry for our upcoming product. As part of this, during the charging, we would like to charge the battery as well as power a load simultaneously. However, we do not want to use the BAT pin for both these purposes. That is, the BAT pin will be connected to the Battery alone. Is there another provision as part of this charger to drive a load? As per our understanding, the SYS pin can be used for this purpose. But, we do not have sufficient information from the datasheet to make our design. Please let us know the following information to proceed with out design:

1. Can we use SYS pin to power/drive a load (the load will be a boost converter) while charging?

2. If SYS pin can be used for this purpose, what is the maximum current and voltage that can be supplied to the load? Will there be a voltage/current fluctuation during the charging phase?

We look forward to hearing from you!!

Thanks

  • 0
    TI__Guru 57321 points

    Hi,

    VSYS can support load. When VBUS is present, VSYS has to be lower than VBUS (buck converter).

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 70 points

    Hello Ning,

    First of all, thank you for the response.

    We are planning to provide a VBUS of 5V as input to BQ25606 charger IC. We need to charger the battery at 2A and power the load simultaneously. From your previous response, I understand that SYS pin can be used for powering the load.

    From the Section Typical Applications of the datasheet, we understand that it is possible to have Ichg as 2A and Isys as 2A. Please let us know how to set Vsys and Isys. Is there a design involved for setting these parameters? If not, how are these parameters determined.

    Thanks and regards

  • 0 in reply to Jaya krishna
    TI__Guru** 105590 points

    Hello Jaya,

    The charger can supply up to 3A from VBUS to VSYS and VBAT through the buck converter, the charger can also control the current to make sure VSYS remains above VSYS_MIN if the system requires more power by supplementing the system current from the battery as well.

    You could supply 2A to supply and 1A to charge the battery, but 2A to both the battery and system would be too high for the charger to supply.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hello Wyatt,

    Thank you for your kind reply.

    I understand that a total of 3A can be used for charging the battery and powering the load. In this case, how should the charging current be designed? I know that the Rchg should be designed to set the charging current. Let's say that I have set the charging current to 3A by fixing Rchg. In this case, if the load is connected, will the Ichg be automatically adjusted so that the load draws the required Isys? 

    Or should I set Ichg to a lower value (like 2A) so that the remaining current can flow to the load (that is there is no auto adjustment of Ichg). Please advice.

    Thanks and Regards

  • 0 in reply to Jaya krishna
    TI__Guru** 105590 points

    Hello Jaya,

    You should set the ICHG to what you want the battery to charge at, not the full system load with the battery. If you refer to section 8.2 Functional Block Diagram in the datasheet you can see the current for ICHG is referenced only going to the battery.

    You should use ILIM for your adaptor, the charger will supply the appropriate current to charge your battery at the ICHG value and then supply the system as well, the system takes priority over charging, so if ILIM is maxed, the battery charging current will reduce to supply the system.

    Sincerely,

    Wyatt Keller