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Original question:

BQ25792EVM: About Quiescent battery current in VBUS connected condition

BQ25792: About battery leak current in VBUS connected condition

Tsukui Yusuke
Guru 21930 points
Part Number: BQ25792


Hi,

Let me ask the following questions in the thread below.
e2e.ti.com/.../4090314

Customers are investigating battery leak current when VBUS is connected to supply VSYS.
I got the following answer in a previous thread.
>The battery voltage is not used to power the converter, only power from VBUS.

However, when the battery leak current path was investigated, the following was found.
・In the case of ”VBUS=5.14V ,VBAT=4.86V, Charging stopped state” condition, quiescent battery current increased. The actual measurement is about 380 μA.
・At this time, the input current to the BATP pin was 2.4uA.
・VSYS is no load. And VSYS voltage was set to 7V and no leakage current was confirmed via the BATFET diode. 

From the above background, the battery leak current is clearly used in the internal circuit.
And Battery leak current is reduced by using Hi-Z mode.
From these facts, it can be seen that the battery leak current is used for the internal converter.

Could you tell me the details of the current value input to the BAT pin under the condition that VBUS is connected?
I would like to know how the battery leak current is consumed when charging is stopped with the VBUS connected.

Regards,
Yusuke



  • 0
    TI__Mastermind 32285 points

    Tsukui,

    I'm sorry to say we don't characterize battery leakage current when VBUS is attached.

    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Guru 21930 points

    Hi Ethan,

    Thank you for your response.
    >don't characterize battery leakage current when VBUS is attached.
    I understood that.
    We check the current value on the actual application.

    However, the customer wants to specify the path where the leak current is consumed, regardless of the specific current value.

    ・Does the built-in converter use both VBUS power and VBAT power?
    　Is the behavior we are checking correct?
    　I don't know what path the battery leak current is used for.
    　Please explain the details of the leak current consumption path.
    　Customers believe that if VBUS exists, IC and VSYS power should only be used from VBUS.
    　Because the battery power is gradually consumed when charging is stopped.

    ・Is there any way to reduce the battery leak current other than using Hi-Z mode?
    　When using Hi-Z mode, VSYS power cannot be supplied from VBUS.
    　Could you give me your advice？

    Regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 32285 points

    Tsukui,

    I repeated your test and I got 63.85 uA drained from the battery with VBUS=5.14V ,VBAT=4.86V.

    Unfortunately, we do not know where the battery leakage current is going in this state.

    I do not know the specifics of your customer's application, but I'd recommend leaving charging enabled when VBUS is attached. You can control how often and how long the battery charges by adjusting the recharge threshold register and the termination current register.

  • 0 in reply to Ethan Galloway
    Guru 21930 points

    Hi Ethan,

    Thank you for your kind support.
    Let me ask you the last question.

    When I checked the battery leak current when connecting to VBUS,
    It was related to the operation of the internal charge pump.
    When the charge pump for SDRV drive was operating, the battery leak current was rising.

    1.
    Is there a way to stop the charge pump with VBUS?

    2.
    How does the charge pump power supply switch between supply from VBUS and supply from BAT?





    Regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 32285 points

    Yusuke,

    The charge pump initially draws power from BATP and then switches to BAT.

    1. Unfortunately, there is not a way to stop the charge pump.

    2. The charge pump is always powered from the battery.

    The charge pump current draw will be reduced if the shipFET is not installed and SDRV is tied to BAT through a 1000 pF cap.

    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Guru 21930 points

    Hi Ethan,

    Thank you for your response.
    >1. Unfortunately, there is not a way to stop the charge pump.
    I understand.

    >The charge pump current draw will be reduced if the shipFET is not installed and SDRV is tied to BAT through a 1000 pF cap.
    Customer have tried the above method on EVM.
    However, the battery leak current did not decrease.
    Have you confirmed this leak current reduction method with EVM?
    Please tell me the circuit example when using EVM just in case.

    Regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 32285 points

    Tsukui,

    I tested a different EVM in a 1S configuration with 5.13 volts input and 4.2 volts output. For the lowest current, I removed JP30, the VBUS/VBAT pullup. I set the HIZ bit to 1. With the shipFET installed, I measured 13.5 uA. With the shipFet not installed, I measured 13 uA.

    I also tested on an EVM in a 2S configuration with 5.13 volts input and 4.86 volts output with the same setup. With the shipFET installed, I measured 82 uA. With the shipFet not installed, I measured 81 uA.