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BQ24120 changing safety timer duration in circuit

Mark Gordon
Expert 3400 points
Other Parts Discussed in Thread: BQ24120

A customer is applying the BQ24120 in a system that has two charge profiles. One is when they are plugged in to a wall and Icharge is 800mA. The other is when they are plugged into a USB host and the charge current needs to be 120mA. The system switches in a resistor in parallel with Iset1 to change the fast charge rate. Battery capacity is 2200mAhr. Currently they have the Cttc set at 470nF ( 20Hr/20min).

I'm being asked if they need to switch in two seperate values for Cttc under each of these conditions as well. They would prefer not to. What risks do they run if they leave the timer significantly long for the fast charge case? Is this a reliability concern.

 

thanks,

  • 0
    TI__Guru**** 150790 points

    No, the IC will be fine.  Completely disabling the timer is allowed by the device.  Another option for them is to set the timer for the higher charge current and then to pull TTC high when they are running at the lower charge current, thus disabling the safety timer but not charge termination.

    Please note that you posted to the external forum.