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Power good pin is not low

George
Intellectual 440 points
Other Parts Discussed in Thread: BQ24072

Hi,

BQ24072  is used as a charger IC in my project. The output of the IC is linked to  a LDO, which is intended for system power supply. The system power voltage is within normal range. Currently, battery is not attached.

But he PGOOD pin of BQ24072 is always in high-impedance states. BQ24072 is fed via USB BUS.

What is the reason for my problem?

Thanks

  • 0
    TI__Genius 11480 points

    Hi George,

    Can you measure the input voltage coming in from the USB to make sure that it is properly supplying power?

  • 0 in reply to David Wiest Jr
    Intellectual 440 points
    Hi David,
    The voltage is 4.72V. There is a TVS tube between the USB connector and the input pin of BQ24072.
    Regards
  • 0 in reply to George
    TI__Genius 11480 points
    George,

    4.72 should be okay for charging Li-Ion cell. A couple things to try:

    I am assuming you measured 4.72 at the In pin on the IC. If this is the case, how are you "reading" the npgood pin? Are you using a microcontroller (and are you using a pull up or pull down resistor)? Or are you using an LED as an indicator (if so, is npgood connected to the anode or cathode?)


    You can also try removing the TVS tube between the USB connector and input pin. That may be causing the issue. If it works without the TVS tube, you may have to explore different TVS options.
  • 0 in reply to David Wiest Jr
    Intellectual 440 points
    David,
    Your are right that the voltage is measured at the input pin. The npgood pin is connected to an LED at the cathode for indicating the input state. If nPGOOD is pulled down to vss level by the IC , the LED in series should light on.

    In fact, sometimes,when i plug the usb cable in, the LED lights on for about 2s or so, and then ,it light off. Thus, I am assuming the LED is connected at the right node. But i can not figure out the cause of its light-off.

    Another thing, currently the battery is not attached to the charging connector, so the current on the vbat pin is zero, but the nCHG pin is always at vss level, as indicated by an led configured the same as nPGOOD pin.

    Regards
  • 0 in reply to George
    TI__Genius 11480 points
    Hm, that is strange. Do you think I could see a schematic/ board layout to get a better look at what's going on?

    If your system power is correct, that indicates that your power is good. Looking at the datasheet, it seems that there are three conditions when nPGOOD would be Hi-Z
    1) Vin < Vuvlo (if you input is always 4.72 V, then this is ruled out)
    2) Vin > Vovp (same as above)
    3) Vin < Vbat +Vin(dt) (if the IC treats no battery as 0V, then this will also be ruled out.If it treats no battery as ~infinite or floating, then this may be what is causing nPGOOD to be Hi-Z. What happens if you insert battery?)

    You say that the nCHG pin is always pulled low in this case. This may seem like an obvious suggestion, but can you verify that the nCHG and nPGOOD lines haven't been mixed up? It seems like a low-hanging fruit, but crazier things have happened.