• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 520 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.

BQ77915: Load removal threshold

Jesse van der Zouw
Expert 1045 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ24650

A PCB with the BQ77915 protection and BQ24650 charger is not recovering by load removal.

When I plug in the charger, which is directly attached to the pack via protection on the PCB, the pack recovers.

I would like to get the load removal recovery working as well.

From what I understand from the datasheet, once OCD is triggered, LD pin wants to pull low.

If there is a load attached which pulls up, that is not possible. Apparantly the charger is seen as a load.

I measured the LD pin voltage on the PCB after OCD was triggered, which was 3.6V (Rld=500k)

I increased Rld to 3.3M, so that Vld can go below 1.25V to trigger recovery, but now OCD does not trigger at all.

What would be a good solution?

  • 0
    TI__Guru 54715 points
    Hi Jesse,
    I'm not an expert with the bq24650, but you have different conditions to consider. One of those which you don't mention is your system connection and load.
    When the charger has power from an adapter but the battery is protected, the battery voltage would be expected to be low. Whatever system is connected to the charger and battery will add load. If the battery has a fault such as OC, its output would be low if held by your system, as you mention it is trying to return the output to the battery voltage with the RLD_INT and RLD_EXT, or about 200k + 500k. Current will vary with the battery voltage, at 18V you would expect about 18V/700k = 25.7 uA. The charger should also be in its battery detection cycle, see figures 12 and 13 and the related discussion in the data sheet. Since the charger has loads in the mA range it should control the battery node.
    If the charger does not have power to the adapter it will provide a load of IBAT to the battery terminals, about 15 uA. The pull down of the system will add to this load and the bq7715 pull down will act on both.
    You will need to analyze your system load and consider the conditions where you want to allow recovery. Adjusting RLD_EXT is an option, but you must allow LD to be pulled above the threshold if you want it to stay protected after OCD.
    You may need some additional control in your system to shed load or provide a definite recovery condition.