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TPSM84824: Output Capacitor Selection

user6360548
Prodigy 50 points
Part Number: TPSM84824

Hi Team,

We are considering using TPSM84824.

The datasheet has the following description about Cout.

At Vout=0.8V, Minimum Required Cout
CERAMIC 300uF and POLYMER 220uF

Can I use only ceramic capacitors?

Ex.)
Murata GRM32ER60G337ME05L (330uF/3225/4V) x1
and
Murata GRM32ER60J227ME05L (220uF/3225/6.3V) x1

Regards,
Hasegawa

  • 0
    TI__Mastermind 35115 points

    Hi Hasegawa-san,

    Yes, it is ok to use ceramic caps. However two things to be careful of if doing so.

    1. With ceramic caps, need to account for derating. For example using muRata's simsurfing tool, the 330µF cap will derate to ~230µF at 0.8V DC and 0.01Vrms AC.
    2. When using these higher valued ceramic caps, be careful of the resonance frequency being too close to the loop fco. Again using the 330µF as an example, the resonance frequency is ~300kHz. This is fine for the 0.8V output application with the TPSM84824 because the loop fco should be around 1/10th the fsw, near 30 kHz.

    Le me know if you have any additional questions.

    Anthony

  • 0 in reply to Anthony F
    Prodigy 50 points

    Hi Anthony-san,

    Thank you for your reply, but my question was below.

    When Vout = 0.8V, can I use the ceramic 220uF instead of polymer 220uF?

    Is it okay?

    Or are the polymer caapacitors not always necessary?

    Regards,
    Hasegawa

  • 0 in reply to user6360548
    TI__Mastermind 35115 points

    Hi Hasegawa-san,

    It looks like I left out one key word in my response to make it clear. Yes, it is ok to use all ceramic output capacitors. The key thing to watch out for in this application is the derating that needs to be applied to a ceramic capacitor's capacitance. It may take either 2x 220µF or 1x 330µF to have at least the same amount of capacitance as a 220µF polymer.

    Let me know if you have any further question.

    Anthony