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BQ24075 battery positive and negative pins getting shorted, blowing up

Sowmya Akella22
Prodigy 80 points
Other Parts Discussed in Thread: BQ24075, TPS63002

Hi,

We are using the BQ24075 power management IC for our proto boards.

The circuit consists of a Li-ion battery of 3.7V, which the IC charges. Another input is from an SMPS which gives 5V 1A. The output of this IC goes to a buck boost converter IC – TPS63002 in order to converter the 5.5/battery voltage to a constant 5V. The circuit is as per the typical application circuit. The Sysoff pin is pulled down with a 100K resistor in order to turn on the IC.

The circuit worked fine till a month back. Off late we are having issues with it.

As soon as I placed the battery (with no input SMPS supply), the battery positive and negative pins got shorted on the IC and it started burning up. This happened on another board as well on which we placed a new BQ24075 IC.

We removed the IC and checked the board if the battery terminal connections were getting shorted somewhere, but they were fine.

Any ideas on what the problem is?

  • 0
    TI__Expert 7730 points
    When you say the positive and negative of the battery are shorted, were they both zero? The bq24075 schematic looks ok and it should not have shorted the Battery to the ground. There's a FET between BAT and OUT, when there's no power from the IN pin, the battery will supply the current to OUT through the BAT FET.
    Did you try removing the boost/buck converter from the OUT pin?

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Prodigy 80 points

    What I meant was the battery positive and negative pins on the IC were showing connectivity.

    Would grounding the battery negative through a resistor be of any help ?

    Well, in the two boards where the IC burnt, the buck boost IC was connected to BQ24075 OUT.

    Thanks,

    Sowmya

  • 0 in reply to Sowmya Akella22
    TI__Expert 7730 points
    On the IC, the battery positive pin is BAT and the negative pin is the VSS. So are you saying the BAT pin and VSS pin are shorted together? Do you know what is the voltage at the output under this condition? It is not likely that the two pins on the IC will be shorted. Can you try to isolate the problem by disconnecting the boost/buck converter from the board and see if the same issue still happens?

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Prodigy 80 points

    Sorry for the late reply.

    Yes, the Battery positive and Vss pins were shorted together as soon as I inserted the battery.

    I did check the battery voltage on one of the boards where the IC didn't burn, there was no output voltage.
    (Here the buck boost converter IC was disconnected)

    Could one of these points be the reason ?

    a) Sudden insertion of the battery caused a voltage spike and burnt the IC

    b)A thermal pad soldering issue caused this , this is where I have my maximum doubts.

    Thanks,

    Sowmya