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BQ2057 possible CV mode?

Frank D'Aliesio
Intellectual 715 points
Other Parts Discussed in Thread: BQ2057

My customer is using your BQ2057 in a new design.  He configured it very much as it is shown in Figure 4 of the datasheet. He gets basic functionality but it does a goofy thing, the status line is toggling up and down (resulting in both status LEDs being lit at the same time).

The DC input is a solar panel and he's charging a 3.7 volt lithium Ion battery. The IC must be in CV mode because the battery voltage is not changing. It’s like the voltage loop is unstable, he can see chatter on the FET gate.  Any suggestions?

Thank you,

Frank

  • 0
    TI__Genius 11680 points

    Also from the customer,

    I mentioned that the power source is a solar panel. The specs for the panel shows that it cannot deliver enough current to be concerned about. I don’t want the BQ2057 to limit available energy to the battery as long as the charger is in constant current charging mode. I used a 0.082 ohm current sense resistor to give me plenty of margin. Would a resistor that small mess up the fully charged decision making process inside the IC?

  • 0 in reply to Nate
    Intellectual 715 points

    Customer also states:

    I use a solar panel as the charging energy source. When I am in constant current phase of charging, I want the pass transistor turned all the way on. This allows the solar panel to deliver as much current as the present solar conditions allow. The consequence of doing this is that the chip VCC voltage gets pulled down close to the battery voltage. I see that the recommended minimum Vcc is 4.5 volts, battery voltage will be below 4.2 volts during constant current charging. Do you think this is my problem?