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BQ25896: BQ25896 Boost mode

Part Number: BQ25896
Other Parts Discussed in Thread: BQ25895


In my circuit 12V is the Vin that is used step down to 5V and then 3.3V for powering the microcontroller and other peripherals. Also 12V is used to charge the battery.

Whenever the 12V is absent the booster circuit automatically boost the battery voltage to 5V. 

I selected the BQ25896  IC for battery charging and boosting. While going through datasheet. I have a doubt in boost mode of  BQ25896 and BQ25895  integrated Buck boost battery charger IC.

As per datasheet Boost mode  enable in

1. BAT above BATLOWV

2. VBUS less than BAT+VSLEEP (in sleep mode)

3. Boost mode operation is enabled (OTG pin HIGH and OTG_CONFIG bit =1)

4. Voltage at TS in range

5. After 30 ms delay from boost mode enable

So my doubt is how the microcontroller give i2c command to buck boost IC when 12V is not present and if  it's 30ms taken for after command in the mean time board will goes to off.

If you can suggest an standalone buck boost having Single Li-ion battery charge current 1 to 2A and discharge current 2A. 

  • Hello, 

    I have a couple questions so that I can better understand your intended design which will help to recommend the most appropriate product. 

    -Do you have a buck converter to step down 12V to 5V before the BQ25896? Therefore is 5V is the input rail to VBUS pin of BQ25896? 

    -Does your microcontroller need to operate off a 5V rail? On BQ25896 when VBUS input supply is removed the battery will automatically power the SYS pin output. If your I2C host is powered from SYS even with 12V removed I2C commands can be sent. 

    if  it's 30ms taken for after command in the mean time board will goes to off.

    There will always be a short period of voltage drop at the input to allow the device to transition from charge mode to boost mode. If you need the board to never go off I recommend you have a separate boost part connected to the SYS output. 

    Best Regards,


  • Hello,

    In circuit there is a dedicated Buck converter for converting 12 V to 5V. The Micro controller is powering from 3.3V. Here by sharing the basic power conversion block diagram of circuit. If you can suggest a good Booster circuit IC.


  • Hello, 

    If you configure your system so that battery never drops below 3.3V you can power the micro controller from SYS directly. If you determine your design requires a boost circuit at the output of battery charger to insure board never turns off please make a new post so the appropriate expert can give a boost converter IC part recommendation given your requirements. 

    Best Regards,