The low esr tantalum capacitor

2024-07-20

A practical capacitor is a non-ideal component. Its circuit model contains series inductance (ESL) and series resistance (ESR). Although equivalent series resistance is often shown in circuit models as a constant value, it varies depending on operating conditions. ESR is resistance from a combination of energy loss mechanisms under specific operating conditions.

Some energy losses within a capacitor can be attributed to the conductors while others involve the dielectric material. These losses vary mainly depending on voltage and temperature. The most common energy loss mechanisms include dielectric losses, ferroelectric losses, dielectric conduction losses, interfacial polarization, partial discharge losses, ohmic resistance losses, sparking between conductors, electromechanical losses, and eddy current losses.

Together with its capacitance value, ESR defines a time constant for charging and discharging of the capacitor and thus how quickly the capacitor reacts on voltage/current changes/ripple. In practical smoothing applications, capacitor technologies are combined in parallel, where high capacitance parts are taking care of bulk filtering (aluminum or tantalum capacitors) and small MLCC capacitors with low ESR are taking care of fast, high-frequency spikes.

ESR in Tantalum Capacitors

The anode of tantalum capacitors is made of tantalum metal powder sintered particles. However, foil style tantalum capacitors (not so commonly used anymore) use a strip of a foil. A layer of oxide is used as the insulator, and its thickness determines the voltage rating of the capacitor. Manganese dioxide or conductive polymer is the second conductors in solid tantalum capacitors used to cover the oxide layer. In the case of foil style capacitors, the electrolyte is the second conductor. In both solid tantalum and foil style capacitors, additional materials are used to make terminations.

In tantalum capacitors, the main contributors of equivalent series resistance are losses in the contacting materials and oxide insulators. At high frequencies, oxide insulator losses are less significant as compared to contact material losses. However, at low frequencies, oxide insulator losses are more significant.

Oxide losses in tantalum capacitors increase slightly with an increase in temperature. In comparison, the resistance of manganese dioxide decreases with an increase in temperature. Furthermore, manganese dioxide resistance losses vary depending on manufacturing procedures, and they are complex to analyze. Conductive polymer tantalum is featuring lower ohmic resistance losses – lower ESR – compare to MnO2 conventional types and it has practically no change of ESR with temperature, unlike MnO2 where ESR at negative temperatures can be around 10x higher compare to those polymers.

At low frequencies, notably below 1 Hz, dielectric absorption and leakage current have a significant effect and should be considered. Generally, in a typical tantalum capacitor, ESR decreases with an increase in frequency. ESR affects the performance of tantalum capacitors in many ways. To start with, its resistive effect causes heating in capacitors. Secondly, ESR increases impedance in circuits, thereby making tantalum capacitors less effective for decoupling and filtering applications.

Low ESR (Equivalent Series Resistance) tantalum capacitors are specialized capacitors designed to have very low internal resistance. ESR is a crucial parameter in capacitors, especially in applications where high-frequency performance, stability, and efficiency are important.

Here are some key points about low ESR tantalum capacitors:

1. ESR Definition: Equivalent Series Resistance (ESR) refers to the inherent resistance in capacitors due to their construction and materials. Low ESR capacitors have minimized this resistance, which is beneficial in various circuit applications.

2. Applications: They are typically used in circuits where stable voltage regulation, filtering, and high-frequency response are critical. Examples include power supplies, decoupling applications in digital circuits, and filtering in audio equipment.

3. Advantages:

• Improved Efficiency: Lower ESR reduces power losses in the capacitor itself, leading to higher efficiency.
• Better Stability: They provide more stable performance, particularly in circuits sensitive to changes in impedance or frequency.
• High-Frequency Performance: Suitable for applications requiring rapid charge and discharge cycles, as well as filtering at higher frequencies.

4. Construction: Low ESR tantalum capacitors are constructed using special techniques to minimize the internal resistance. This often involves using conductive polymer materials or other advanced electrolytes.

5. Considerations:

1. Voltage Rating: Ensure the capacitor's voltage rating matches or exceeds the application requirements to avoid failures or reliability issues.
2. Polarity: Tantalum capacitors are polarized, so correct orientation in the circuit is crucial to prevent damage.

6. Alternatives: While tantalum capacitors offer low ESR, they can be more expensive compared to alternatives like ceramic capacitors. Ceramic capacitors, especially those with Class II or Class III dielectrics, are also used where low ESR is needed, though they may have different characteristics in terms of temperature stability and capacitance change with voltage.

In summary, low ESR tantalum capacitors are specialized components designed for applications demanding high performance, stability, and efficiency. They are particularly useful in modern electronic devices where maintaining signal integrity and power efficiency are paramount.