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BQ24770: System Voltage when BATFET is turned off (NVDC)

Jay Yoo
Intellectual 1826 points
Part Number: BQ24770
Other Parts Discussed in Thread: BQ25720

Hi team,

My customer is designing BQ24770 and asked following questions regarding system voltage in NVDC. Could you help answer this questions?

1. Could you confirm if it is a normal behavior that the system voltage is ~200mV above than the battery voltage when BATFET is off(Charging disabled)?

Please refer to below customer's charging profile. Also, from what I found in BQ25720's datasheet, there's a comment that it is normally 150mV above than the battery voltage.

2. What is the value for the BQ24770 then? I couldn't find in the datasheet. 

3. If you don't mind, Could you please explain why there is a voltage difference when the charging is done?

BQ25720 datasheet comment:

Thanks,

Jay

  • +1
    TI__Mastermind 18685 points

    Hi Jay,

    1. It is normal to have the system voltage ~200mV higher than the battery voltage when BATFET is off. 

    2. From the test, the voltage difference is about 200mV. 

    3. The NVDC required a small voltage difference between the system rail and battery rail. This NVDC voltage avoids turning on the BATFET or discharging the battery when system power is available. At the same time, the battery can quickly supplement the system when needed. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    TI__Intellectual 1826 points

    Thanks for your kind explanation, Tiger. 

    regards,

    Jay