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BQ24266 ---/CHG status when Battery is absent

tiper liu
Prodigy 250 points
Other Parts Discussed in Thread: BQ24266

Hi, All:

I am using BQ24266 in a product. I am confused by the /CHG status when the battery is absent.

In spec, /CHG should be high impednace status when the battery is absent.

But when I plug into 5V power source, and no battery is used, the /CHG is low status ,and the the LED is turn on. ( it indicates on charging period, but I don't use the battery)

I test your EVM, if no battery is used, and the TS pin is pulled high( no battery ), the condition is the same with my test.if pulled TS to low(GND), /CHG is high impedance.

  • 0
    TI__Mastermind 25800 points
    Hey tiper,

    So for your product, the /CHG status will indicate a charging period due to the recommended decoupling capacitor on your BAT pin. This capacitor as seen by the charger, looks like a "mini" battery that is charged and discharged very rapid.

    As for our EVM, when TS pin is pulled high, it does not disable charging, only the TS function internally. Because of this, the decoupling capacitor on our EVM exhibits the same charge characteristic as your product.

    When the TS pin is low, you have effectively placed the part into the "T_HOT" temperature state, which disables charging altogether.

    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 250 points
    Hi, Joel:

    Thanks for your replay in advance.
    Do you means if I take away the CAP in BAT Pin and Pull Ts to High level, the /CHG will be high impedance status?
  • 0 in reply to tiper liu
    TI__Mastermind 25800 points

    Hey tiper,

    Please disregard my previous reply.

    After taking a look at the part again, the bq24266 and that family of parts (bq2426x) have a battery detection feature, so the capacitor does not play a role in this issue.

    What is most likely happening is a TS fault for your device (i.e. the TS voltage is too high or too low, triggering a TS fault). This fault also shows as a /CHG low status, meaning the LED will turn on.

    That is why the LED is on in our EVM. The EVM has a potentiometer to simulate TS temperature faults, and if the resistance is too high or too low, you will fall into one of the TS fault conditions.

    Bottom line: Leave the capacitor in. You do not have to pull TS high. Make sure TS voltage falls within this range:

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 250 points
    HI, Joel:

    Thanks, I understand you meanings . I will try to adjust the resistors ( let the Ts voltage falls between Vhot and Vcold).

    But I have a question, when we pull Ts to GND directly , Ts will also be out of the range , why is the /CHG is

    high impedance status and doesn't indicate Ts fault?

    thanks
  • 0 in reply to tiper liu
    TI__Mastermind 25800 points
    Hey tiper,

    When you pull TS to GND directly, the /CHG should be LOW because V_TS is recognized as T_hot to the charger.

    How are you pulling TS to ground? And is this on our EVM?

    Regards,
    Joel H