BQ24618: Reliability improvements

Hi Boris, 

Thank you for reaching out!

Could you please elaborate on the observed behavior? 

Best Regards, 

Aya Khedr 

Hi Aya,

Thank you for your reply.

With reference to the schematic, TP3 (VBUS), TP2 (ADAPTER+) and the load side of R2 all measure 20.2V, which means that PD is correctly negotiated. TP1(CHG_OUT) however measures 4.9V, instead of the expected 16.8V. There is no sign of any mechanical damage to the PCB itself, nor any hot spots (the BQ IC measures around 60C). Also, the STAT LEDs show charging in progress even though no battery is connected.

I hope this helps.

Kind regards,

Boris

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,

Thank you for looking into this.

I am actually working remote this week and do not have access to the hardware, so I will get back to you mid next week.

Regards,

Boris

Hi Boris, 

Thank you for the update. 

I look forward to hearing back from you soon. 

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 Boris, 

Thank you for capturing. I would be interested to see this waveform on a failed unit if possible. 

Best Regards, 

Aya Khedr 

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, 

Are you testing these units with the battery disconnected or connected?

Could you also do an ABA swap by placing a working unit onto the board that is not working?

Best Regards, 

Aya Khedr 

Hi Aya,

The tests so far have been done without a battery connected.

Replacing the broken IC fixes the issue and the battery charges as normal.

Kind regards,

Boris

Hi Boris, 

The battery charger's typical charging profile assumes a battery is connected. 

Please let me know if you have additional questions. 

Best Regards, 

Aya Khedr

Hi Aya,

Thank you for your reply, although I do not understand how it explains the failures.

Is a unit more likely to fail if not connected to a battery when powered on?

Regards,
Boris