Hello,
We are using the BQ24618 for a 4S charging application. The product has been on the market for some time now and we have not had any major issues with the design. In rare cases however, we have had some chargers whose BQ chip has failed after very little use.
As we are planning to incorporate the charger into a future product, any feedback on how the reliability of the current design can be improved is appreciated.
I am attaching the schematic and layout design.
Thank you!
Boris Yanchev
Hi Boris,
Thank you for the clarification.
I reviewed the schematic provided and have a couple comments below:
1- The best stability occurs when the LC resonant frequency is within the range of 12kHz-17kHz for the BQ24618.
2- For charge current = 4A, the typical inductor value is 6.8uH and the typical output capacitance is 20uF (see below)
I would like to further identify why the battery voltage is 4.9V instead of the expected 16.8V.
Could you please provide a scope capture upon power up similar to the waveform below?
Best Regards,
Aya Khedr
Hi Aya,
The battery voltage is 4.9V on the unit that failed, working units have the correct voltage.
Here is the scope capture you requested of a working unit.
(1 Vcc, 2 /PG, 3 Vref, 4 REGN)
Kind regards,
Boris
Hi Aya,
Here is a capture of a failed unit. The battery voltage is 4.9V and the status LEDs show charging even though no battery is connected.
Kind regards,
Boris
Hi Boris,
After doing more analysis on the waveform above, it looks like the REGN voltage on the failed unit is higher than we expect (circled in red).
This voltage should be regulated at ~6V (similar to what is seen in the normal waveform).
It seems that there may be damage to the REGN pin which would then cause the battery output voltage to be incorrect. Unfortunately, I am unable to definitively say why REGN voltage is abnormal without knowing what caused this.
Best Regards,
Aya Khedr
