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MSP430FR2355: Capacitance and necessity of decoupling capacitors

O.H
Mastermind 6480 points
Part Number: MSP430FR2355


Hi experts,

Q1:The capacitance of the Decoupling and Bulk Capacitors connected to the power supply (DVCC, AVCC) is recommended to be 4.7uF to 10uF, is this capacitance mandatory?
My customer is considering FR2355, but would like to use a smaller capacitance from the viewpoint of explosion-proof design.

Q2:Is the following recognition correct for decoupling capacitors other than power supply?
If an external reference (VEREF+/-, VREF+) is not used, a decoupling capacitor is not necessary.
If an external reference is used, a separate a decoupling capacitor is needed in addition to the power supply.

Best regards,
O.H

  • +1
    TI__Mastermind 28075 points

    Hi O.H.

    O.H said:
    Q1:The capacitance of the Decoupling and Bulk Capacitors connected to the power supply (DVCC, AVCC) is recommended to be 4.7uF to 10uF, is this capacitance mandatory?
    My customer is considering FR2355, but would like to use a smaller capacitance from the viewpoint of explosion-proof design.

    We strongly recommend bulk caps in those values. You can probably operate the device without them, but not having them can negatively impact performance.

    O.H said:
    Q2:Is the following recognition correct for decoupling capacitors other than power supply?
    If an external reference (VEREF+/-, VREF+) is not used, a decoupling capacitor is not necessary.
    If an external reference is used, a separate a decoupling capacitor is needed in addition to the power supply.

    Can you elaborate more on what you mean here? I can say that recommendation would only apply to the external reference. So you would need a bypass capacitor if you use an external reference, in addition to all other bypass capacitors we recommend. In general I don't recommend they omit any of the bypass capacitors mentioned in the datasheet. 

    Best Regards,
    Brandon Fisher

  • 0
    Guru 24805 points

    I am not sure why you need to limit such tiny energy storage devices. Especially for something that should be safely within an enclosure.

    The purpose of those capacitors is to provide a low impedance power supply. The low ESR of the caps along with the short low inductance connections to the package provide that.

    You could maybe sidestep that by otherwise providing a low impedance power source. But it would be hard. Voltage regulators have a low impedance output. Some better than others but all increasing with frequency. So low impedance connections to the regulator, Vcc AND Vss, are required.

  • 0 in reply to Brandon Fisher94
    Mastermind 6480 points

    Hello,

    Thank you both for your replies. The answers you gave me helped me understand.

    Best regards,
    O.H

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