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TPS22918-Q1: About input capacitor

Lee, Sam
Expert 4965 points
Part Number: TPS22918-Q1

Hi team,

I’d like to confirm below sentence in the datasheet of TPS22928-Q1.

 

In case that 30uF capacitor are used at the input path of the other device after the output of TPS22928, should the input capacitor still be 10 times higher than the output capacitor? Otherwise, is a 1uF okay? Can you recommend the appropriate input capacitance for this case?

 

9.2.2.1 Input Capacitor (CIN)

To limit the voltage drop on the input supply caused by transient in-rush currents when the switch turns on into a

discharged load capacitor or short-circuit, a capacitor must be placed between VIN and GND. A 1 μF ceramic

capacitor, CIN, placed close to the pins, is usually sufficient. Higher values of CIN can be used to further reduce

the voltage drop during high-current application. When switching heavy loads, it is recommended to have an

input capacitor about 10 times higher than the output capacitor to avoid excessive voltage drop.

Thanks,

Sam Lee 

  • 0
    TI__Mastermind 32650 points

    Hi Sam,

    The input capacitor is used to mainly protect the supply from large transient spikes. In most use cases a 1uF capacitor is sufficient to offset this.

    We would recommend increasing the input capacitance in the event you were charging a larger capacitive load like a cap bank. In your case with an output capacitance of 30uF, we believe that a 1uF input capacitance is fine.

    Do note that another way to minimize inrush current is by increasing the rise time of the switch with the CT pin.