Crossing an MLCC Cap to a Tantalum Cap


#1

Lately it has been harder and harder to find the correct MLCC caps in stock that many people have been looking for due to supply shortages. In the long run this is going to be fixed by the manufacturers tooling up their production lines. This however does not help many of our customers that are currently needing these parts.

In talking with my product manager and we discussed the possibilities of crossing some of our MLCC customers to Tantalum caps. Though not the most popular suggestion we did have some positive feedback and Wilmer Companioni at Kemet was able to come up with some suggestions for our customers to look at. Here is a slide he put together for the Kemet line of KO caps.

Looking through this chart Wilmar touched on several key parameters you need to look at if you are considering crossing from an MLCC to a tantalum cap. I have summarized them below.

Capacitance

Tantalum caps in the same package size tend to have more capacitance than the same package size MLCC. The smallest value Digi-Key has at the time of this post is .47uF The chart above shows 680nF as that is the smallest KO series cap currently available. Tantalum will not be a good replacement if your needs are lower than this. One option Tantalums give is the ability to replace a bank of MLCCs with one tantalum cap. This can result in a cost and space savings.

Voltage

When looking at tantalum-based capacitors you will be limiting your voltage. Many tantalum caps are considered high voltage when over 35V. This means if your operating voltage is greater than 50V crossing to a tantalum capacitor will likely not be a viable solution.

ESR

ESR is one area that MLCCs generally have a lower rating rating than comparable tantalum counterparts. Now there are lower ESR tantalum caps, however if this is a high priority you may have a hard time finding a cross going from MLCC to tantalum.

Frequency

When looking at tantalum caps you want to pay attention to the self-resonant frequency.If you are operating above 1 MHz switching frequency you may be beyond the limits of a tantalum cap.

Reverse Bias

Tantalum capacitors are polarized and as such, they can not take reverse bias voltage. If the capacitor is placed in a location which reverse bias is possible or needs to be tolerated,tantalum caps will not be a suitable solution.

MLCC Cross Conclusion:

As you can see finding a cross is possible although at times won’t be available or feasible, This post is simply being offered as a place to look if you are in an MLCC crunch and need to find a solution to move forward. If you have any questions please post a reply to this post and we will try our best to answer.

For a more in-depth look at crossing MLCCs to tantalum caps and each of the parameters take a look at the article from Wilmer Companioni Here:


#2

Any experience with customers accepting a tantalum cross for a ceramic one?
Lately we are getting more and more customer for crosses in stock. But they want to remain in the ceramic caps.


#3

I’ve taken several of these calls myself. I’ve found it pretty effective to try and work with the customers to see if they can wiggle on the exact values, tolerances, voltage rating (going up is often easy), temperature grades, etc. for what they need.

Often it’s just a purchaser you are talking to so you have to work back to an engineer in charge or give the purchaser advice to take back to the engineer(s).

As an example, if you are trying to cross a 0.1 uF cap, well, the odds are pretty decent that every use of that cap on a board is just a decoupling cap. Ask the design engineer (via the purchaser if necessary), if that’s the case and if so they most likely could switch to a different common value entirely (0.15 uF, 0.22 uF, etc.).