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BQ29200: VDD over voltage protection for 29200

Part Number: BQ29200

Hello, we are experiencing a lot of 'swollen' batteries from the field lately due to field personnel using the wrong adapter supplying VDD. When this occurs, the 29200 allows VDD across one battery (2 18650 in series) which obviously is way beyond the max rating. Obviously, the way to fix it is for them to use the correct power adapter however... hasn't happened yet!

Just wondering if there's a easy solution to sense the over-voltage condition on either battery and disable the 29200? We have a very limited board space.


Dan Ross - AST

  • Hi Dan,

    If VDD is going across a single cell, I would assume that would trigger the OV condition on the BQ29200. This should trigger the OUT pin to drive high, which we recommend connecting to a fuse so that the battery pack can be disconnected from the load or charger. See Figure 9 in the datasheet for more details. 

  • Hello Shawn, thanks for the reply and sorry it's taken me so long to get back with you. I believe now it's not a simple thing like an over voltage condition from the charger  however, something is causing the 29200 to take out batteries by dumping VDD across a cell. The charge disable signal is tied to ground so the 29200 is always enabled. Looking at the datasheet there's a  recommendations regarding disabling the 29200 if VDD is below 6V. I'm thinking out loud here, what if the field personnel violates this and populates our charger then plugs in the adapter for the charger last? Could this cause a problem with the 29200 in that it will be enabled before VDD rises above 6V.

    Looking at the internal diagram, I'm wondering in particular what's controlling the 2 front FET'S when VDD is below 6V.

    Thanks much.

  • Hi Dan,

    I am a little bit confused on the customer scenario. If the customer is connecting the OUT pin directly to GND, there is no protection enabled. Does the customer just want the cell balancing functionality of the device?

    The datasheet recommends disabling cell balancing when VDD is below 6V, but not the entire functionality of the device. This recommendation is to avoid prematurely discharging the cells, as the cell balancing features requires current to be drawn from the cells. If your customer is not worried about that, then it is up to them to choose whether they follow that recommendation or not.

    As long as the CB_EN pin is configured for cell balancing, the balancing will occur.

  • Shawn, the only intervention the customer has with the battery pack is putting on and removing it from the charger to use in another product of ours. When the product fails due to a 'won't charge' condition, they send it back here. I'm curious now, the on-board 5V regulator in the 29200 feeds it's logic. If the regulator can't properly function until VDD reaches 6V, what is controlling the logic and in particular the 2 FETS on the cell inputs? Could this be what's causing the 29200 to dump VDD across one cell?

  • Hi,

    Could you please clarify the answers to my questions in the previous post? Is the customer only using the device for cell balancing and not over voltage protection?

    As I previously stated, the device will balance the cells if the CB_EN pin is configured to do so. Cell balancing is not encouraged when VDD < 6V not because of the regulator, but because doing so would drain the batteries even more. I do not believe this is the reason VDD is going across a single cell. If the device is configured properly, it will protect the cells from this kind of scenario.

  • Hi Shawn, for cell balancing.

  • Hi Dan,

    I would strongly advise using the over voltage protection on the device to prevent potentially dangerous situations, like the cell swelling you have described.