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BQ76942: BQ76942 REGIN and BREG transistor

Babu Vishwanath Hemath Kumar
Prodigy 230 points
Part Number: BQ76942

Hello to all,

I know that BQ76942 is suitable for 3s to 10s li-ion cells. My doubt is 

1) What is the use of BREG and REGIN pin?

2) Why the transistor of BREG and REGIN pin connected in between the CHG and DISCHG Mosfet?

3) I have a plan to control the CHG and DSCHG MOSFET using the micro-controller, in that case do I need to use the transistor that has been used in BREG and REG pin?

4) Does REGIN and BREG transistor has any link with REG1 pin?  

Please clarify my above doubts

  • +1
    TI__Mastermind 42050 points

    Hello Babu,

    1) What is the use of BREG and REGIN pin?
    BREG is the output of the pre-regulator REG0, which is used to drive the base of a BJT to supply ~5.5-V to the REGIN pin. The REGIN pin is used to power the REG1 and REG2 LDOs. This is explained in Section 12.3.1 Preregulator Control of the datasheet.

    2) Why the transistor of BREG and REGIN pin connected in between the CHG and DISCHG Mosfet?
    This can be connected to either the top of the battery stack or in between the CHG/DSG FETs as you pointed out. The REGIN requires a voltage of ~5.5-V, so the voltage is step-down by using the BJT and BREG regulator. I am not entirely sure why it was placed in the common-drain point in the EVMs, my guess would be so that the regulators could be powered through a charger or battery when the device is under a fault. The body-diode of the FETs could also serve as a way to protect the regulator from reverse currents if the FETs are off, although a diode is usually recommended placed in this path in order to achieve this.

    3) I have a plan to control the CHG and DSCHG MOSFET using the micro-controller, in that case do I need to use the transistor that has been used in BREG and REG pin?
    You only need to use the BREG/REGIN BJT if you are planning on using LDOs REG1 or REG2. These can be left floating if the LDOs are not used.

    4) Does REGIN and BREG transistor has any link with REG1 pin?  
    Yes, these are used to power the REG1/REG2 LDOs. See Section 12.3 LDOs of the datasheet.

    Best Regards,

    Luis Hernandez Salomon