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TLV62568A: Input and output capacitors

Part Number: TLV62568A

Hello,

At the datasheet of the TLV62568A at  the typical application section the suggestion for the output capacitor is Murata ceramic capacitor, 22uF / 6.3V (GRM21BD70J226ME44), and for the input capacitor the suggestion is ceramic capacitor, 4.7uF / 10V (GRM21BR71A475KA73L).

I couldn't find these capacitors capacitance -frequency chart, but from previous experience I know that ceramic capacitor has rapid decrement of capacitance when the frequency is higher than 1MHz.

Since the TLV62568A  is working at 1.5MHz, at the input, the current is drawn from the capacitor t 1.5MHz, and at the output the ripple is at 1.5MHz.

Doesn't the capacitance at this frequency less than what it should be?  Why the suggested capacitors are ceramic and not Aluminum or polymer?

Also, is it sufficient to put 10uF ceramic capacitor at the output?

Thanks for your help,

Asaf Abraham

  • Hello Asaf,

    Thank you for coming to us with your queries.

    Typically, the capacitance increases as the frequency rises, especially at the MHz range. Please refer to the graph below from Murata, including the link.
    Ceramic capacitors are suggested components for the input and output filtering because it has low ESR (a few milliohms range) and ESL (~100pF range). On the contrary, the Aluminum and polymer capacitors have much higher ESR and ESL at the ~MHz frequency range, which will result in a larger ripple voltage.

       Capacitance vs. Frequency (https://ds.murata.co.jp/simsurfing/mlcc.html?lcid=en-us)

    TLV6256xA does not support a capacitor with nominal value of 10uF as indicated in the datasheet. See the LC matrix below reference.

    I hope I was able to address your queries.

    Best regards,

    Excel

  • Hello Excel,

    Thank you for your detailed reply.

    We try to use the 10uF capacitor, since the 22uF capacitor we wanted to use, has a rapid decrement of capacitance over frequency.

    The capacitor 22uF we wanted to use is: C1608X5R1A226M080AC by TDK:

    As you can see from the Capacitance to frequency graph, the capacitance decreases when the frequency increases.

    I looked at some other manufacturer and other technologies (X7R) and saw similar graphs. The capacitance  decreases over frequency.

    Also, at all the capacitors, when looking at the impedance graph, it seems that after about 1Mhz, the capacitor behavior is more inductor than capacitor.

    So, except of the ESR issue, should I still use ceramic capacitor?

    Also, How can the Murata capacitor have different capacitance over frequency graph?

    Best regards,

    Asaf

  • Hello Asaf,

    Thanks for the quick response.

    Understood. With C1608X5R1A226M080AC, the capacitance decreases significantly at frequency ≈ 1MHz, which is not the case for Murata capacitor. Unfortunately, I don't have data to check the accuracy of the graph from Murata. In any case, the GRM21BD70J226ME44 (Cout) was used during the IC validation stage, so I'm confident it works in your application too.

    Please use a ceramic capacitor as input and output capacitors. Aluminum or polymer capacitors have never been used for this device.

    Let me know if you have additional queries.

    Best regards,

    Excel

  • Hello Excel,

    Thanks for your quick and detailed response.

    I have no additional queries.

    I believe you gave me the information I need Slight smile

    Best regards,

    Asaf