Over the past ten years or so, ceramic capacitors have made great strides in volumetric efficiency. 1 µF used to be the biggest you could get, and now, at a low voltage, you can get 470 µF in a small SMT package. And, stacked capacitors for switch-mode power supply applications are allowing high values in higher voltage ratings – up to 500 V. Ceramics have some serious advantages over tantalum and aluminum types, with lower ESR and leakage, and longer lifetimes. They do have voltage rating limitations – as we will talk about later.
Stacked ceramic capacitors from AVX
AVX makes stacked ceramic capacitors with ratings from 50 to 500 V and capacitance of up to 400 µF in X7R and 1,300 µF in Z5U temperature coefficients. A stable COG coefficient is also available. For a height of 0.240 inches, you can get 10 µF ±10 percent in a 50 V, X7R temperature rating that is 0.40 inches square. Its part number is SM045C106KAN240 and it can be had with a number of SMT or thru-hole lead configurations. In the same height, you can get 160 µF if you don’t mind a width of 1.35 inches and a 2.05-inch length. They are not inexpensive, the 10 µF part costs about $10 ea./1,000. They are also available in military styles MIL-PRF-49470 and the SMX style is available for high-temperature applications up to 200°C.
AVX makes a good point about the ESR of MLCC (multi-layer ceramic chip) capacitors with the following chart:
Typical ESR Performance (mΩ)
Aluminum Low ESR Solid Aluminum Electrolytic Solid Tantalum Electrolytic MLCC MLCC 100μF/50V 100μF/10V 100μF/16V 100μF/50V 4.7μF/50
ESR @ 10KHz 300 72 29 3 6
ESR @ 100KHz 280 62 20 2.5 15
ESR @ 1MHz 265 56 17 7 7.5
ESR @ 10MHz 560 91 22 20 14
AVX also has its TurboCap line of “High CV SMPS Capacitors” stacked devices, like the ST203C227MAJ10 220 µF, 25 V, ±20 percent, X7R. This stacked ceramic part is 1.025 inches long, 0.22 inches wide and 0.30 inches tall. ESR at 100 KHz is ~1 mΩ and it costs $22 ea./25+.
Fig. 1: AVX offers the ST203 TurboCap series of stacked ceramic capacitors.
It may be worth looking at leaded MLCC devices, such as the radial lead SkyCap/SR series from AVX. The 10 µF, 50 V, X7R with a 0.20-inch lead spacing (SR655C106KAR) is in stock and costs about $1.82 ea/500.
Fig. 2: AVX SkyCap leaded capacitors offer 10 µF at 50 V.
Taiyo Yuden’s very-high capacitance
Taiyo Yuden, one of the leaders is high-value MLCs, offers a 470 µF, 4 V device in a 0.177 x 0.126 x 0.098 (1812) SMT package that is not stacked. It has a X5R temperature coefficient with 20 percent tolerance. ESR at 1 MHz is 4 mΩ. The AMK432BJ477 will cost you $4.00 ea./500.
Samsung offers the 220 µF 6.3 V X5R 20 percent SMT ceramic CL32A227MQVNNNE in a 1210 package for about $0.71 ea./500.
Watch the voltage coefficient
Remember, the X5R rating covers -55° to 85°C with a ±15 percent capacitance shift over temperature – but, applied voltage is another matter. For the Taiyo Yuden 4 V part there is a 5 percent drop at 1 V, and a 40 percent drop at 3 V and a 55 percent loss at 4 V. The voltage coefficient tends to vary with package size and gets better with larger packages. For X7R or X5R coefficients you should, in general, figure a 30 percent capacitance drop at 40 percent of the maximum applied voltage.
You can get an NPO dielectric capacitor that will not have significant temperature or voltage effects, but you are limited to a maximum value of only 0.47 µF at 50 V in a 2220 (0.220 x 0.197 inch) package. This value is available from Kemet (among others) as the C2220C474J5GACTU and will cost you $2.11 ea./1,000.
Fig. 3: The Taiyo Yuden SMT capacitor family reaches 470 µF.
Aluminum electrolytic capacitors are very stable over applied voltage, and actually go up a few percent as rated voltage is applied. But, they are large, have a high ESR, and have some long-term reliability issues.
100 µF SMT parts are common
Quite a few suppliers make a 100 µF MLC SMT X5R device with a 16 V rating – and we have seen where the higher voltage rating is important when using the X5R or X7S dielectrics, so this may be the sweet spot at the moment. The Taiyo Yuden EMK325ABJ107MM-T comes in a 1210 package with an X5R coefficient and costs just $0.78 ea./500. The stacked 2220 size CKG57nX5R1C107 capacitor from TDK is ±20 percent, and costs about $2.15 ea./1,000. The CC1210MKX5R7BB107 ±20 percent in a 1210 package from Yageo is only $0.62 ea/500 and the C1210C107M4PACTU X5R 20 percent from Kemet comes in a 1210 package for about $0.84 ea./1,000.
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