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BQ25190: BQ25190 Output Capacitance Clarification

Tyler Sisk
Prodigy 40 points

Part Number: BQ25190

Hello,

We are using the BQ25190 for power management in a new portable device we are developing. We are utilizing both the Buck and BuckBoost converters to power different blocks. In the datasheet, section 8.2.2.2 discusses output capacitor selection for various outputs of the chip. My question is do the maximum capacitances listed apply to the attached loads as well? For example we have a 10uF capacitor placed right next to the IC on the BuckOut pin. We have a microcontroller + peripherals that specifies around 50uF in total decoupling caps which we would like to attach to the Buck output. Would this cause a problem since the maximum allowable capacitance is 25uF on the Buck output? Would an acceptable "isolation" strategy be to add a ferrite bead between the supply output capacitor and downstream load capacitors?

Also, there is no maximum listed for the BuckBoost which I just wanted to confim has no limit? It seemed odd to me that there are maximums listed for the SYS output and Buck output but not the BuckBoost.

  • 0
    TI__Mastermind 18975 points

    Hi,

    I believe this is primarily in relation to the decoupling capacitor at the device output pin but not necessarily as total capacitance at the output node of the device. Let me confirm this with the device designers.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 40 points

    Hi Juan,

    Thank you for the follow up. I will await what the design team has to say. I just want to avoid any possible instability issues etc if the capacitance is too high.

    Best,

    Tyler

  • 0 in reply to Tyler Sisk
    TI__Mastermind 18975 points

    Hi Tyler,

    Understood, I'll share an update when it becomes available.

    One thing to note is the 25uF is for the effective capacitance, do you know what the effective capacitance will be at the voltage that you're operating?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Mastermind 18975 points

    Hi Tyler,

    I was able to confirm that that specification is selected to reduce potential stability issue so it is best if effective capacitance is kept below 25uF for total capacitance on the line. As I mentioned before the effective capacitance on this pin is likely to be lower depending on the voltage you plan to operate at. 

    Best Regards,

    Juan Ospina