Why LOW ESR Matters for Tantalum Capacitor

ESR (Equivalent Series Resistance) is the sum of all resistive components that constitute the impedance of a capacitor. Therefore, it is a thermal loss characteristic. When capacitors are in operation, ESR also affects the magnitude of charging and discharging currents. In solid tantalum capacitors, the impedance components contributing to ESR include:

 

1.Solid electrolyte system (MnO2)

2.Dielectric layer (Ta2O5)

3.Terminals, leads, and other components connecting to the PCB

 

Manufacturers of solid tantalum capacitors can make improvements in physical design and materials to reduce the overall ESR of the capacitor. Capacitors with lower ESR generate less heat internally, thereby enhancing overall circuit efficiency and long-term reliability. Lowering ESR also increases the current during capacitor charging and discharging, thereby improving circuit performance.

 

Tantalum capacitors are exceptionally well-suited for two primary functions: high-capacity energy storage and ripple filtering. We will discuss these applications in more detail below.

 

In addition to maximum operating voltage and voltage derating, a crucial characteristic of capacitors is their ability to store charge. Some applications require capacitors to store large amounts of charge. Solid tantalum capacitors have highly stable capacitance values, making them ideal for high-capacity energy storage. They are widely used to maintain voltage stability during peak current demands. Two factors must be considered in this regard:

 

First is the total capacitance required to supply the necessary energy. In some cases, a single tantalum capacitor is sufficient, but more stringent applications may require multiple capacitors in parallel to increase total capacitance while reducing the combined impedance of the array.

 

The second factor is the ESR (Equivalent Series Resistance) of the capacitor. A lower ESR allows for increased current transfer, reduces voltage drop during discharge, and improves circuit performance.

 

An example of this is providing large-capacity capacitors for powering a microprocessor with a 3.3V power supply. During operation, microprocessors in high-performance applications must meet substantial current demands. Capacitors effectively provide the necessary energy capacity, often referred to as "slew rate," defined as the conversion from reactive current to peak current at a specific slope expressed in "Amps/μs". During peak demand periods, rail voltage may need to be maintained within a specified range (e.g., voltage drop less than 10% = 0.33V). Capacitors with low ESR can deliver higher discharge currents while reducing heat generation, meeting these requirements more quickly and efficiently.

 

Designers typically place several low-capacitance multilayer ceramic capacitors (MLCCs) near the processor for short-term power supply, while adding larger capacitors (tantalum, polymer, or aluminum electrolytic capacitors) further away to meet long-term current demands. MLCCs with ultra-low ESR can deliver very high transient currents, but their limited capacity means they can only provide the required current for a short period. Subsequently, large-capacity capacitors are used to fulfill circuit requirements. By using low ESR tantalum capacitors in such applications, designers can reduce reliance on MLCCs, decrease the number of components required, save PCB board space, and reduce component costs. Additionally, this approach helps enhance board-level reliability by leveraging more robust structural design.

 

 

Another advantage of using low ESR tantalum capacitors as large-capacity capacitors is the reduction of heat generation during charge/discharge processes. This can improve circuit efficiency and lower the operating temperature of the circuit. Additionally, it allows for the use of smaller power supplies, further reducing costs.

 

Using low ESR capacitors to smooth signals can reduce ripple currents in DC buses, such as output filter capacitors in switch-mode power supplies (SMPS). This improves the voltage ripple during waveform peaks and valleys and the charge/discharge currents of the power supply. By reducing ripple currents (peak-to-peak), less heat is generated during each charge/discharge cycle. Low ESR (low inductance) capacitors also facilitate effective use of ripple filter capacitors for high-frequency AC noise components in circuits.

 

UF Capacitors supply CA45 Low ESR Chip tantalum capacitors. (website:www.ufcapacitors.com)

Cross Reference details as below:

Photo	UF Capacitors Series Code	Kemet	AVX	Vishay	NEMCO	NICHICON	Panasonic	EPCOS	Samsung
	CA45U Series	T494 Series T495 Series	TPS Series F93 Series	593D Series 594D Series TR3 Series	LSR Series	F91 Series	TEL Series	B45197 Series	SCE Series

 

 

 

 

 

 

 

 

 

 

 

In addition to ESR, designers of filter capacitor designs must also consider rated voltage, ESL, DCL, and dielectric characteristics. Tantalum capacitors typically employ very thin and compact designs, with robust structures that achieve high reliability at the PCB level.

 

 

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