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BQ24192: Bypassing BATFET externally on BQ24192

Sarth%20Dave
Prodigy 140 points
Part Number: BQ24192
Other Parts Discussed in Thread: LM3478, TPS61088

Hello,

We are using the BQ24192 on one of our client's boards to charge 3.7V, 1S12P lithium ion battery pack. Following is the power tree that we have on board, 

Battery (3.4-4.3V) --> Boost Converter (LM3478) (4.5V) --> Boost converter (TPS61088) (12V). The power tree described here is not an exhaustive one but it will serve the purpose. We have an external DVR being powered from the 12V boost converter. Whenever we start the supply to the DVR, we have observed an inrush current of ~12A for 0.5-1 us on the 12V line. Due to this event, the battery current from the BQ24192 shoots to >13A and the internal BATFET turns off as per the description in the datasheet.

To bypass the BATFET this, we see there already is an opinion on one another thread to put a PMOS in parallel with the BATFET and to have the PMOS controlled by the host (Link). However, we are not wanting to do a design change in the board (since we already have ~200 nos manufactured) and instead, we came up with an idea of bypassing the BATFET with an external resistor with a value of 10mohm. For protection of the board and battery incase we bypass the BATFET as described, we have the following measures:

  1. Battery PCM for protection against overcharge/over discharge/over current/ over voltage & under voltage
  2. A PTC fuse in series with the battery with a trip current of 11A and holding current of 6A
  3. A 4A PTC fuse on the charging side of the BQ24192

Kindly have a look at this solution and let us know whether there are any ill-effects of using this solution to either the board, battery or the charger IC itself. Do let us know if you require more information on this. 

PS : We already have tested this solution from both charging and discharging sides and since then, it has seemed to function well.

We appreciate any suggestions/feedback on this.

Regards,

Sarth

  • 0
    TI__Mastermind 26010 points

    Hi Sarth, 

    I cannot comment on any ill-effects of the solution related to your specific battery. I recommend you reach out to the battery manufacturer for comment on how the solution would affect the battery performance. 

    In general as long as the battery can discharge at high currents I do not see an issue relating to having a parallel discharge path from BAT to SYS to avoid triggering the BATFET overcurrent protection.  Although, I do have one potential concern for charging. Does your solution have a way to disconnect the external resistor path during charging? You mention you have tested the solution during charging, does charge current flow through the external resistor as well as the BATFET? 

    Battery charge current is monitored and regulated at Q4 BATFET, if charge current is able to flow from SYS to battery via the external resistor during charging the BQ24192 is not able to properly control the charge current during the different phases of charge. 

    Best Regards,

    Garrett