Ceramic capacitor resilience to overvoltages?

[cupoftea]

Hi,
We are doing a Buck with Vin=24-32V, VOUT=13V5 AND iOUT = 15A at 450kHz.
When its input connector is suddenly "Hot plugged" with a 32V input supply, the voltage on its 10uF, 50V MLCCs peaks up to
56V for a few microseconds. They are only rated 50V....do you think this will cause premature failure if it happens say ten times a day for
5 years?

(PNG and LTspice attached)

 

[D.A.(Tony)Stewart]

It could trigger a fire hazard before 10 years depending on the supplier quality.

Even the best , Taiyo Yuden, say you should never run at rated voltage for reliability reasons, let alone over voltage.

The damage with high ripple current with Junction heat is perhaps a bigger factor. If degradation causes higher ESR, your surge overvoltage may reduce but operating ripple V and temp rise may increase. Higher ESR increases the temperature, then failure rates will double every 10'C rise above room temp.

The real effect is hard to predict, but reliability Failure in Test (FIT) rates certain accelerate with the ratio of rated voltage, even if when new they might work at twice the voltage a few times.

"It is not guaranteed to use our products over the rated voltage. Please agree to that in advance." TY

 

[FvM]

Another point to consider is the C/V characteristic of X5R and X7R capacitors. It can be as bad as below (Murata X5R 1206).

--- Updated Apr 18, 2024 ---

Only slightly better, X7R capacitor CL31B106KBHNNNE (Samsung)

--- Updated Apr 18, 2024 ---

Did you verify 50 % capacitance at 24V for your capacitor?

 

[D.A.(Tony)Stewart]

I suggest you safely protect the caps with an OVP plan

E.g. TVS of suitable Joule size