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If the charger stops running after the load is switched on, no battery, where to look at? (The first thing to do)

sviss
Expert 1530 points
Other Parts Discussed in Thread: BQ24113A

Hello. I'm fairly new to battery management, and 'd like to find the first thing to look at when the charger malfunctions.

Device: BQ24113A. Schematic: exaclty as is the datasheet's sample schematic. Charger: 9v 500mA walljack. Load: secondaty DCDC switcher, no load (~200mA startup current), no battery.

I have 2 boards, same schematic, ~same value (to my belief and to 5% tolerance) components, slightly different (to 2cm/1in trace lengths) layout.

The first board works OK (with the battery, or without). The BQ24113A on the second board stops running (no pulses @ the inductor) as soon as the secondary DCDC is switched on (output voltage drops to below 1v) and starts up again if that DCDC is switched back off. I have 2 copies of the "board 2" - same problem. If I connect the battery, the BQ24113A seems to run OK on the "board2" too.

So, where woold you look at at first? (at second ... :-) Please suggest.

Thank you.

  • 0
    Prodigy 20 points

    Hi. As seen you have a problem with PCB footprint . Try to add RC filter :  R=1K between pin 14 and +BAT and  C (10-100nF)from pin 14 to GND.

     P.S.: See page 6 in datasheet :" BAT... - Battery voltage sense input . Bypass it with a 0.1 uF capacitor to PGND if the a long inductive leads to battery ."

     

  • 0 in reply to yuri6525
    Expert 1530 points

    Thank you Yuri for your help.

    Because as I said the Bat+ is loaded with secondary DCDC converter, there is a good 10uF ceramic capacitor at the input of that DCDC, i.e between Bat+ and Gnd. So extra 1k+100nF will hardly do.

    The problem is with PCB layout? Most likely this is the case.

    Guess, you meant: "the first thing I'd do == I'd look at the BQ24113A.14 pin and try find there some noise".

    OK I'll try and post results here.

  • 0 in reply to sviss
    Expert 1530 points

    Hi, there. I've found the problem. It was not a bad part, nor bad layout. It was a bug (my error).

    As a real newbie I connected (as described above) secondary DCDC to the battery, not to the charger output (before current sense resistors).

    Hope in the next datasheet edition the right point for load to connect will be suggested (for dummies).

    BTW, why isn't current measurement resistor shunted (with on-chip shunt) if charger voltage drops?

     

  • 0 in reply to sviss
    Prodigy 20 points

    I find application in datasheet:

    Figure 18. Application Circuit for Charging a Battery and Powering a System
    Without Affecting Termination

  • 0 in reply to yuri6525
    Expert 1530 points

    Yes, Yuri. I know this ad. 

    This small picture added bulk of few extra days to my design timeline.

    This (fig.18) app circuit works if the battery is connected, but does not if not.

    One must add an ecap of at least 330 microfarades in parallel with the battery.

    Now everything works. Thank you.

    Done. Closed.

  • 0
    TI__Prodigy 720 points

    This is because when DCDC starts, it draw current, the output voltage drops too much.

    When output voltage drops below 2V/cell, charger considers as short circuit, so curren limits to 50mA.