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BQ24296: Current limit to the Sys pin via Bat pin in Battery discharge mode

Shreenidhi Patil
Expert 3936 points
Part Number: BQ24296
Other Parts Discussed in Thread: LM3478,

 

Hello Team ,

We had used Battery charger for a 1s Pack & the sys pin of Battery charger Output goes to LM3478 booster Input.

LM3478 Output needs 5.5V, 3.5A Current.

 

We are facing the issues with the Voltage drop at the Vsys Pin as well as with the Current requirement by the Booster IC. this is mainly due to the  high input current flowing in the BATFET from Bat pin to SYS pin .

 we tried to Isolate the Battery Charger & then we have connected Battery directly at the Booster Input & we have seen that we are able to get the 3.5A current from Booster Output which seems that Booster Circuit is being OK.

 

Then We connected the Battery Charger again & we are seeing that whenever Load asked at the output of boost  is 2.7A  Booster Output goes down to 3V from 5.65V due to the drop of the voltage and available power on the sys pin .

 

We have found out the Pin Compatible Part which shows "BQ2419X" series in which below line has written:

 

What do you suggest?

Can we order some samples meanwhile & tried the same at the place of BQ24296? We suspect the main issue is the current limit of BATPIN to SYSPIN  of BQ24296.

 

Do you see any Risk to use the BQ2419X series in place of BQ24296? please let us know if  Any Hardware change?

Please provide all your suggestions relates to Current BQ24296 part as well as BQ2419X series.

 

Looking forward to your soonest response.

 

  • 0
    TI__Expert 8230 points

    Hi Shreenidhi,

     For an Iout of 3.5A @ 5.5V, we can approximate that 6-7A are needed from the battery to support the load; this current is enough to trip the OCP of the bq24296(minimum is 5.5A and typical is 6.6A). This can be confirmed by monitoring the battery current during testing, in particular the inrush current from the battery into the LM3478.

    The bq2419x does provide higher OCP thresholds than the 296, but it's important to very the magnitude of the current we are dealing with to ensure the inrush current doesn't exceed the limitation of the bq2419x as well.

    The bq2419x does have a pin difference from the 296, note that pin 12 is QON while on the bq2419x, pin 12 corresponds to TS2 (there are 2 TS pins in the bq2419x family, they can be tied together if using a single thermistor).