Putting ESR to work

As smartphones and tablet PCs add further features and functions, power efficiency has moved into the focus of design efforts. TDK’s new YNA series of noise absorbers effectively suppresses noise in DC-DC converters and antiresonance in decoupling circuits without reducing the efficiency of power supplies.

DC-DC converters in the power supplies of smartphones can generate high-frequency EMI, including what is known as voltage ringing. This is due to the highspeed switching of their semiconductor components such as MOSFETs. In order to suppress the noise and protect the semiconductor components, an RC snubber circuit is typically connected in parallel to the input stage of the power supply. Because standard capacitors are optimized for low ESR values, their use for EMI suppression always requires an additional resistor to maintain sufficiently high impedance levels in order to complete an effective resonant circuit. While the classic RC snubber circuit can effectively suppress EMI and voltage ringing it reduces the efficiency of the power supply by up to around 4 percent. For this reason, such circuits are not considered ideal for smartphones and other mobile devices that need long battery life.

Figure 1:

Impedance of a capacitor in a resonant circuit:
At the self-resonant frequency (SFR) of the capacitor, the impedance depends only on the capacitor’s ESR value.

YNA noise absorber saves components

Therefore, in order to suppress noise without power losses, TDK developed the YNA noise absorber. Thanks to its intentionally higher ESR, this multilayer EMC component is able to suppress EMI and voltage ringing without an additional resistor. As such, it can replace a capacitor in the input stage of a DCDC converter (Figure 2). Voltage ringing occurs when the impedance drops at the self-resonant frequency (SRF) of the capacitor in the RC snubber circuit. When a YNA series noise absorber is used, both horizontal and vertical EMI radiation can be reduced effectively by up to 3.5 dB (Figure 3).

Figure 2:

Basic circuit diagram of a DC-DC converter:
The TDK YNA series of noise absorbers can replace a capacitor in the input stage of a DC-DC converter.

Figure 3:

Noise suppression in a DC-DC converter:
When a TDK YNA series noise absorber is used, both horizontal and vertical radiation can be reduced effectively by up to 3.5 dB.

Innovative electrode design for selectable ESR 

The YNA series of noise absorbers offers a space-saving and power-efficient solution. The multilayer components feature a 3-electrode design (Figure 4), consisting of two terminal electrodes and one external electrode that is not connected to the circuit (NC electrode). The third electrode, however, is connected to the internal electrodes. The ESR of the component can be manipulated by varying the number, combination and pattern of internal electrodes connected to the NC electrode.

Figure 4:

Electrode configuration of the TDK YNA series of noise absorbers:
The TDK YNA series of noise absorbers feature two terminal electrodes and one external NC electrode that is connected to the internal electrodes but not to the circuit.

Suppressing antiresonance in decoupling circuits

In addition to its excellent performance in suppressing EMI and voltage ringing in DC-DC converters, the YNA series of noise absorbers can be used effectively against antiresonance in decoupling circuits. Because a single capacitor is unable to cover the entire frequency range from low to high, decoupling circuits generally combine multiple capacitors with different magnitudes. The aim is to give low impedance over a wider band and thus curb the influence of voltage fluctuation.

Antiresonance is a phenomenon where the selfresonant frequency (SRF) of two capacitors differs, and parallel resonance occurs in the frequency region where one capacitor is in the inductive zone and another capacitor is in the capacitive zone, causing a high impedance peak and an increased noise current flow, as shown in Figure 5. The result is a sudden change in power supply voltage that can cause jitters and lags over the transmission signal. As a result, logic errors can occur, and in the worst case, the power supply can trigger overvoltage that can damage semiconductor components.

Figure 5:

Preventing antiresonance in decoupling circuits with the TDK YNA series:
The use of standard MLCCs (red curve) with low ESR values in decoupling circuits can lead to impedance peaks (antiresonance) and result in circuit malfunction. By contrast, the TDK YNA series of noise absorbers (blue curve) features selectable ESR values and thus enables stable decoupling without antiresonance.

Because the YNA series of noise absorbers offers selectable ESR values independent of case size, capacitance, or rated voltage, it represents an effective solution for antiresonance. In addition, because this component is manufactured with the same materials and process of standard MLCCs, there are no special restrictions on the design and the layout of wiring on a PCB.

Broad range of selectable ESR values

The new YNA series of noise absorbers is available in three case sizes (IEC 1005, 1608 and 2012). Thanks to its broad range of capacitances and ESR values (Table), it is suitable for reducing ringing noise generated by the power supply in smartphones, tablet PCs and other mobile devices and for preventing antiresonance in decoupling circuits. Thus, the YNA series offers a high-performance noise absorber that can improve power quality with no loss in power efficiency, while reducing the number of parts used.

Table: Key data for the TDK YNA series of noise absorbers