Data Lines

The table shows the variety of USB connectors. While there were still five different types in use for the USB 2.0 standard, the types have consolidated to only two for the USB 3.1 standard. The EU regulation requiring new devices to use USB-C as the charging standard is likely to have further accelerated this consolidation.

The RJ45 LAN sockets with through-hole technology (THT) for printed circuit boards offer increased robustness and mechanical stability. The plastic used, as well as the LEDs with a modified lead frame position, can withstand the higher temperatures of a reflow soldering process. An optimized housing design allows for a uniform reflow air flow to the pins.

The HPLE types of filtered RJ45 LAN sockets feature a second common-mode choke, which ensures better EMI performance above 80 MHz.

The frequency/impedance diagram shows the self-resonant frequencies of the MLCC capacitor types with 100 nF, 10 nF, and 1 nF. The self-resonant frequencies increase as the  capacitances decrease.

The capacitance of a capacitor is typically also dependent on an applied direct current voltage (DC Bias) and can become significantly lower with increasing voltage. From the DC Bias/capacitance diagram, it is clearly visible that with increasing miniaturization of the component, the nominal value of 470 nF decreases (red curve).

For applications with high mechanical stress, it is advisable to use soft termination capacitors. These have a termination with Ag-polymer/Ni/Si and minimize the risk of cracks occurring.

Capacitors should maintain their capacitance as consistently as possible across temperature variations. Three of the materials used, NP0, X7R, and X5R, fulfill this requirement significantly better than Y5V, as can be clearly seen in the diagram. NP0 shows virtually no changes in capacitance over a wide operating temperature range.

Many applications require galvanic isolation in the signal transmission path, such as LAN connections (Ethernet). Signal transformers like the WE-LAN AQ fulfill this task. To validate the transmission path, it can be simulated with LTspice. The diagram on the right confirms the high accuracy of the simulation based on measurements.

The HPLE types of filtered RJ45 LAN sockets feature a second common-mode choke, which ensures better EMI performance above 80 MHz.

When protecting against electrostatic discharge (ESD), a sensitive electronic component (Load) is safeguarded by a parallel discharge path (VDR), which becomes conductive when the breakdown voltage of the protective element (VDR) is reached. In this way, the overvoltage (Transient) does not reach the sensitive load (Load), which would exceed the threshold for system failure, but is instead "clamped" to the clamping voltage.

The various data transmission standards such as RS232, CAN, USB, Ethernet, etc., operate at different frequencies and data rates. The table shows the recommended capacitance values for ESD protection for each.

In data lines, common-mode signals can cause interference and affect signal integrity. A common countermeasure is the use of common-mode chokes. To select the appropriate common-mode choke, it is advisable to refer to the impedance curves over frequency instead of just considering inductance. These can be found on the RedExpert online simulation platform by Würth Elektronik.

With the online simulation platform RedExpert, you can calculate the appropriate impedances of SMT ferrites for your application based on frequency, DC bias, system impedance, and required attenuation.

If your application experiences high peak currents, you should use a ferrite from the series of Multilayer Power Suppression Beads with very low Rdc and a rated current of up to 10.5 A.

When filtering signals on data transmission lines, the impedance behavior of SMT ferrites over frequency must be considered to attenuate the occurring disturbances and not the useful signal.