Part Number: BQ51051B
We have a wearable application using your BQ51051B. The version is the correct one as we have a 4.35V battery.
We experience a random problem that afftects more than 50% of the units. During the charge process, presumibly in the costant current phase, we often see a sudden drop of the current powering the recharging pod.
Starting from that moment, monitoring the battery voltage, we see a significant reduction of the voltage slope.
The chip will go on signalling CHARGE IN PROGRESS (CHG pin).
The transmitter (a off the shelves, Qi certified transmitter, based on a ST chip ) will go on signaling CHARGE IN PROGRESS, but the battery will never reach the voltage needed to switch from constant current to the constant voltage phase. The charge never ends until the 10 hours time out triggers.
At first we thought of a temperature problem, but I tend to exclude it as we are monitoring the temperature carefully and it always remains well inside the safety margins.
Another thing that let me think that it is not a temperature problem is that if you simply remove the device from the pod and put it back again after just few seconds, the charging procedure will immediately restart with the usual charging current.
After this "off the pod - back on the pod" procedure, it is likely that the charge will correctly ends. Other times, another stop could occur and you need to repeat the procedure.
What could be the reason for this behaviour? Any clue? Any area we should investigate?
What is really annoying is that the first 10 prototypes were (and still are) just perfect. Now a significant amount of units of the 100 units of pre - production shows this behaviour.
Theoretically no change of any kind. Just a slight decrease of coil distance (less than 1 mm) that we thought could have been an improvement.
Unfortunately, because of mechanical restriction, is very difficult to test new PCBs with old enclosure.
Thanks
Andrea