• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 443 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24765 dies when battery is disconnected

Mike Wilson
Prodigy 215 points
Other Parts Discussed in Thread: BQ24765, BQ2476, BQ24747

I am using the BQ24765 with BQ20Z75.I believe it is possible to destroy the BQ2476 when the BQ20Z75 disconnects the battery at charge termination.

I am applying "How to Operate Fuel Gauge bq20z7x/8x/9x and the SMBus-Like Smart Chargers bq24747/765 Without a Host Controller" (SLUA533). My fuel gauge circuit is wired the same as BQ20Z75 EVM (HPA214).

I use SMBUS commands from a microcontroller to the BQ20Z75 to turn my load on and off, and the BQ20Z75 never enters "sealed mode."

The BQ20Z75 also turns off the charger - to - battery connection, (See SLUU277, Oct 2007, page 8, Q2 in schematic), and so the charger must withstand the battery being disconnected at any time (at charge termination) (by the  BQ20Z75 EVM (HPA214)) while charging. When it does this, sometimes the BQ24765 fails (likely because of inductor dumping).

I have further tested this on the HPA349 EVM. Leaving the input adapter connected , leaving CE high, and connecting / disconnecting the battery. After a few tries, the BQ24765 no longer charges, and it is obvious that the power stage is destroyed, while the logic portions still function.

What would you recommend to prevent destroying the BQ24765 in my application?

It seems to me that the combining of HPA349 and HPA214 (or HPA059) as in SLUA533 is not a valid combination, in the sense that the BQ20Z75 can disconnect the battery from the charger, causing failure of the HPA349.

Mike

  • 0
    TI__Guru 56650 points

    According to you description, the charger is damaged during disconnecting the battery load while charging. It shouldn't relate to SLUA533 setup. The charger should not be damaged during removal a battery.

    We did insert and removal battery test during IC evaluation. When a battery is removal during the charger, the inductor energy will dump to the output capacitor. The output voltage has overshoot and it could be higher than input voltage. But, the charger still survives because it has cycle-by-cycle OCP, UCP, sleep comparator and all other protection function.

    The EVM output terminal could see a negative voltage during output short or battery reverse plug-in transient. A paralleling schottky diode on the output terminal can protect IC from a huge negative voltage spike.

    The long wire form EVM to the battery can also cause a high voltage spike if the charging current is suddenly cut off.

    Would you help me monitor the output voltage and inductor current? So, we can get more clues.