Ceramic Capacitor Selection for Power Supply Design

𝐂𝐞𝐫𝐚𝐦𝐢𝐜 𝐂𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 𝐒𝐞𝐜𝐫𝐞𝐭𝐬 𝐏𝐚𝐫𝐭 4: 𝐇𝐨𝐰 𝐭𝐨 𝐌𝐚𝐤𝐞 𝐚 𝐋𝐚𝐫𝐠𝐞 𝐌𝐋𝐂𝐂 𝐂𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 𝐭𝐡𝐞 𝐑𝐢𝐠𝐡𝐭 𝐖𝐚𝐲 In parts 1–3 we saw a number of derating effects. In this 4th post, we’ll put that knowledge to good use. 𝐏𝐀𝐑𝐓1: https://lnkd.in/ebfwjwsb 𝐏𝐀𝐑𝐓2: https://lnkd.in/eyKTA98i 𝐏𝐀𝐑𝐓3: https://lnkd.in/e9rnsA4S ✅ Let’s assume we want a 100𝐮𝐅 capacitor operating at 3.3𝐕, and the operating temperature range is -40 𝐭𝐨 +85 𝐂𝐞𝐥𝐬𝐢𝐮𝐬. ✅ We need a capacitor close to the IC, which is a 𝐟𝐢𝐧𝐞-𝐩𝐢𝐭𝐜𝐡 𝐁𝐆𝐀, so we can only fit an 0201 capacitor there. ✅ We also want the capacitance guaranteed over the 𝐥𝐢𝐟𝐞𝐬𝐩𝐚𝐧 of the product, which is 5 years. 2️⃣ In the second picture, you see tables with 𝐁𝐈𝐀𝐒 𝐝𝐞𝐫𝐚𝐭𝐢𝐧𝐠 values of large-value ceramic capacitors. 3️⃣ In the third picture, you see 𝐚𝐠𝐢𝐧𝐠 𝐯𝐚𝐥𝐮𝐞𝐬 for Class II ceramic capacitors. 4️⃣ In the fourth picture, we see 𝐭𝐞𝐦𝐩𝐞𝐫𝐚𝐭𝐮𝐫𝐞 𝐝𝐞𝐫𝐚𝐭𝐢𝐧𝐠 values. 💡 We know from a previous post series and video that large capacitors have an 𝐚𝐝𝐯𝐚𝐧𝐭𝐚𝐠𝐞 ( https://lnkd.in/enJ-zkzp ). So we pick the largest-value 0201 𝐜𝐥𝐨𝐬𝐞 𝐭𝐨 𝐭𝐡𝐞 𝐁𝐆𝐀. 📐 Max value of 0201 is 4.7uF; however, we lose 71% of that due to the 3.3V DC bias, 15% due to temperature, and 12% over its lifespan. 𝐓𝐡𝐢𝐬 𝐥𝐞𝐚𝐯𝐞𝐬 𝐣𝐮𝐬𝐭 1𝐮𝐅 𝐞𝐟𝐟𝐞𝐜𝐭𝐢𝐯𝐞𝐥𝐲!!!!! 📐 A little further away, we can place 0603 parts. The largest value is 47uF, but DC bias loses 66%, temperature 15%, and aging 12%. 𝐓𝐡𝐢𝐬 𝐥𝐞𝐚𝐯𝐞𝐬 𝐣𝐮𝐬𝐭 12𝐮𝐅, 𝐬𝐨 𝐲𝐨𝐮 𝐧𝐞𝐞𝐝 8 (!). 📐 Maybe it’s better to look at 1206. You get 220uF; DC bias loses 61%, temperature 15%, and aging 12%. 𝐓𝐡𝐢𝐬 𝐥𝐞𝐚𝐯𝐞𝐬 64𝐮𝐅. Two of these will leave you with a 29uF margin. 💡 Temperature and DC bias derating do not “add up” one to one, so this leaves us with some extra margin. 💡 So we need to place 444.7uF to end up with at least 100uF over time, temperature, and bias, in what is probably the most economical way. You see how much you lose and how careful you have to be….. ☛ In the next post in this series, we’ll do an impedance simulation of this network. 🎬 I also have a video with more information on ceramic capacitor derating: https://lnkd.in/eV-9sFVn 🎓 And I have a course containing my system I developed over 30 years that gives you a very high chance of your first design meeting crucial specifications—you can watch a free module and get a free checklist here: https://lnkd.in/ews6cwQm Best regards and happy designing, Hans Rosenberg

ESR (Equivalent Series Resistance) is a small amount of resistance that exists in real capacitors due to the materials and construction. It’s not an ideal component—real-world capacitors have this internal resistance that can affect performance.  ESL (Equivalent Series Inductance): The inductive part due to the physical structure (leads, internal plates). It becomes noticeable at high frequencies. At a certain frequency, the capacitance is canceled out by inductance = resonance point. 🔹 High ESL = Bad for: High-frequency decoupling (ESL turns cap into an inductor) Fast switching applications 🔹 Low ESL = Good for: Decoupling at high frequencies High-speed digital circuits (e.g., FPGAs, CPUs) Why ESR is Important: Power Loss & Heating: High ESR = more heat, especially in high-frequency or high-current circuits (like switching power supplies). Filtering Performance: In power supply filters, low ESR is often crucial to smooth out voltage ripple. Stability in Circuits: Some regulators or circuits require a certain ESR range (not too low, not too high) to remain stable How to Choose a Capacitor Properly To choose the right capacitor, consider these main factors: 1. Capacitance Value (µF, nF, etc.) How much charge the capacitor can store. Pick based on the circuit requirements (timing, filtering, energy storage, etc.). 2. Voltage Rating (V) Choose at least 25–50% higher than the max voltage it will see. For a 12V system, pick a 16V or 25V rated cap. 3. ESR Low ESR: Use for switching regulators, power supply filters, and high-speed circuits. Moderate ESR: Sometimes needed for LDO regulators to stay stable. Datasheets will list ESR; some parts even have it labeled as "low ESR." 4. Capacitor Type Ceramic: Low ESR, small, great for high-frequency decoupling. Electrolytic: High capacitance, higher ESR, good for bulk energy storage, power supply filtering. Tantalum: Stable, compact, usually lower ESR than electrolytics, but expensive and sensitive to surges. Film: Very low ESR, excellent stability—great for audio or precision analog. 5. Size & Package Match physical size to your board layout. Bigger caps can usually handle more ripple current and heat. 6. Temperature Rating Common ratings: 85°C or 105°C. Use 105°C or higher for power electronics or hot environments.

Tolerance analysis can be very important not only for analog designs. Digital designs, especially those with high demands on the power supply network, rely on a certain amount of capacitance being present at the operating voltage and over temperature.   The DC bias voltage behaviour of ceramic capacitors is well known, as is the temperature dependence of X5R capacitors in particular. If possible, it's best to avoid the X5R dielectric altogether. However, in some cases, especially for MLCCs in small packages such as 0201 and above a certain capacitance value, the X5R dielectric dominates the list of available components. Often X5R capacitors are the recommended choice in reference designs.   In these cases, where many X5R capacitors are used as decoupling capacitors, tolerance analysis becomes important. Typically, DC bias derating is also dominant at high capacitance densities and, in combination with temperature derating, often leads to a very significant reduction in total capacitance. This can lead to violations of the PDN target impedance or affect the stability of the voltage regulators.   I've noticed that the capacitance of X5R capacitors drops rapidly above the 85°C specification limit. This can limit the usable temperature range of a device if these capacitors are used in local hot spots, such as under power-hungry components in BGA packages.   X6 type dielectrics might increase the number of available components somewhat and provide a higher thermal stability. Nonetheless examining the combined effect of DC bias and temperature at board level temperatures might be very important. #electronics #analysis