Why we replace tantalum capacitors with chip multilayer ceramic capacitors?

There are two main reasons:
The 1st is the issue of reliability. Tantalum electrolytic capacitors have the potential to cause smoke and fire if a short circuit failure occurs. Smoke and fire can be fatal to electronic products equipped with tantalum electrolytic capacitors.

Another issue is the raw material tantalum. Tantalum is a rare metal produced in only a handful of places around the world. Therefore, if there is political unrest in the production area, prices will skyrocket and supply will be unstable. As long as the raw materials are rare metals, users of tantalum electrolytic capacitors cannot completely avoid such risks.

The solution to these problems is to replace tantalum electrolytic capacitors with chip multilayer ceramic capacitors. Chip multilayer ceramic capacitors are far less likely to smoke and catch fire than tantalum electrolytic capacitors. In addition, since no rare metals are used, prices and supply are more stable.

What is tantalum capacitors?

A tantalum electrolytic capacitor is an electrolytic capacitor, a passive component of electronic circuits. It consists of a pellet of porous tantalum metal as an anode, covered by an insulating oxide layer that forms the dielectric, surrounded by liquid or solid electrolyte as a cathode. Because of its very thin and relatively high permittivity dielectric layer, the tantalum capacitor distinguishes itself from other conventional and electrolytic capacitors in having high capacitance per volume (high volumetric efficiency) and lower weight.

What is chip multilayer ceramic capacitors?
A ceramic capacitor is a fixed-value capacitor where the ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes.

There are two main advantages to replace tantalum capacitors with chip multilayer ceramic capacitors.

First, it can reduce the mounting area. Because chip multilayer ceramic capacitors have a large electrostatic capacity per unit volume. The other is to reduce the output ripple voltage when used in output smoothing circuits such as DC-DC converters. The reason is that the equivalent series resistance (ESR: Equivalent Series Resistance) of chip multilayer ceramic capacitors is low. As shown in Figure 1, when using tantalum electrolytic capacitors, the output ripple voltage is 56mV, but when using chip multilayer ceramic capacitors, it drops to 7mV.

▪Be careful when using it for output smoothing

However, the work is not done simply by replacing tantalum electrolytic capacitors with chip multilayer ceramic capacitors. Depending on the use, sometimes there are some issues that need to be paid attention to.

Output voltage waveform when the output capacitor of the DC-DC converter is replaced with a tantalum electrolytic capacitor and a chip multilayer ceramic capacitor. The switching frequency of the DC-DC converter is 300MHz. The capacity of tantalum electrolytic capacitor is 100μF. Use three 22μF chip multilayer ceramic capacitor products. The ripple voltage before replacement was 56mV, and after replacement with chip multilayer ceramic capacitors, it dropped to 7mV.

A typical example is when used in output smoothing circuits such as the DC-DC converter mentioned above. Although chip multilayer ceramic capacitors do have the advantage of reducing output ripple voltage due to their low ESR, the low ESR characteristic is sometimes a "double-edged sword." The reason is that the phase of the feedback loop response characteristics of the DC-DC converter will be significantly shifted after replacing it with chip multilayer ceramic capacitors. In the worst case, there will be a 180-degree offset, causing the output of the DC-DC converter to oscillate abnormally. In this case, the DC-DC converter cannot function.
For this reason, when using chip multilayer ceramic capacitors in an output smoothing circuit, it is necessary to adjust the constants of the phase compensation circuit. If the phase compensation circuit is integrated inside the DC-DC converter IC, it is necessary to measure the ESR of the tantalum electrolytic capacitor that is being replaced, and then insert a resistor in series with the same ESR as the tantalum electrolytic capacitor. Doing so can suppress abnormal oscillations.

See Figure 2 for details. Figure 2(a) shows the output voltage waveform after simply replacing the capacitors that form the output smoothing circuit of the DC-DC converter from tantalum electrolytic capacitors to chip multilayer ceramic capacitors. Abnormal oscillation occurred in the waveform, and the output voltage of the DC-DC converter also changed significantly. Figure 2(b) is the waveform after adjusting the constants of the feedback loop phase compensation circuit. Abnormal oscillations of the waveform are suppressed, and the output voltage is reduced to a level that does not have negative effects. If this output voltage waveform is achieved in actual use, it can be used with confidence.

HONGDA Capacitors, as the leading passive components’ factory in China, the ISO9001:2015 qualified factory, focus on tantalum capacitors, chip multilayer ceramic capacitors, electrolytic capacitors, polymer capacitors, inductors, etc production.
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