Does anyone have any experiences (good or bad) with using MLCC-type caps for input power / voltage regulator applications? I'm using 22uF Tantalums right now and have reduced (but not eliminated) some heavy switching transients. The MLCC looks good in terms of no polarization and reduced package size for the capacitance rating.
Is there a source for these caps (in 47uF or 100uF flavors) at prices lower than DigiKey? DigiKey wants $23.48 for ten 100uF, 6.3V caps. I realize this is a relatively new technology but has anyone run across a more inexpensive source?
Perhaps smaller sizes are cheaper in the end. I've been using MLCC for several years now. They work fine and I like the fact MLCC is not prone to burn a hole in the PCB. Another positive thing about MLCC is that they are better for the environment. Mining tantalum does a lot of damage to the plants and animals.
--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Ceramics are great, and values like 10 or 22 uF are affordable. But a lot of regulators will oscillate into a big ceramic load, including most LDOs and LM337.
Now that's EXACTLY the kind of information I was looking for! Thank you!
So often people get sidetracked by picking on the exact verbiage used to format the questions that they overlook the context of the question...
I had a problem with switching transients on an LDO which a larger input capacitor seemed to reduce. I had been using a 1uF ceramic on the input-side and a 1uF ceramic on the output-side of a TC1108 LDO regulator. Max current draw at 3.3VDC was about 100mA. Per great suggestions form this group, I inserted a larger 22uF Tantalum on the input-side and the problem was significantly reduced. While the switching transient was reduced to the point of not causing a problem with board operation, it was still there, but greatly reduced in amplitude. The voltage dip only dropped to about 2.5VDC from the nominal 3.6VDC input and there was virtually no overshoot when the transient ended about 2usec later. I had thought to increase the size of the input cap to 47uF, 68uF, or even 100uF. I also just found out about MLCC caps (I'm sorry... I must have been living a sheltered life:) ) and saw the reduced size for the footprint as well as the non-polarized components.
Since these components are relatively high cost ($23.48 for 10 parts from DigiKey), would I be wasting time and money to try something like the 100uF
You can solve that problem by adding a little series resistance. DigiKey has a good stock of multiple sizes of SMD resistors with resistances of 5, 10, 20, or 50 milli-ohms, or whatever your choice.
The datasheets for National LM3670 and LM3671 (LDO efficient DC-DC regulators) have reference designs that call for MLCCs, and they provide part numbers.
I want a cap to have a low AC impedance, so it seems silly to add another component just to make esr worse. It's better to use regulators that are stable with low-z loads.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.