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BQ24133: Calculation method for capacitor value of Csys and Cbat

Satoshi
Guru 19645 points
Part Number: BQ24133

Datasheet page-27 is described  "total capacitance of 50 μH connected at PVCC node: 10-μF capacitor for buck converter of bq24133 and 40-μF capacitor for system side".

Is there calculation method for these capacitor value?

For example, below condition should increase capacitor value, is it correct?

・Io=2A, Vo=5V

・When AC/BAT switched (backup power) Δt=10us , Voltage drop (ΔV) should keep 0.1V

　⇒Calculation: CxV = IxT

　　　　　　　⇒ C = ΔIxΔT / ΔV

　　　　　　　　　= 2 x 10u / 0.1 = 200uF

Best regards,

Satoshi

  • 0
    TI__Genius 14360 points
    Hi Satoshi,

    For the datasheet description, it is general condition. It depends on back stage system design.
    When AC/BAT switches, current would flow through the BATFET body diode to maintain system power. It would wait for the break-before-make logic and delay(large than 10us) then turn-on BATFET. There is no power off condition occurred with our design. Your formula is correct but it is based on the power-off condition.

    Thanks,
    Ann Lien