Let's have a look at an example for an EMC compliant interface to absolute position encoders, the TI design, TIDA 00179 with a block diagram shown on the right, highlighted in green, implements and EMC compliant RS485 interface for four wire encoders as well as for two wire encoders with power over RS485. The design was tested for EMC immunity according to the IEC 61800-3 and exceeds requirements for ESD fast transient burst, search, and conducted RF.

A robust RS485 transceiver with built in protection for IECESD and IECEFT was chosen to eliminate cost of external ESD protection diets. Let's have a look at some key parameters selecting a robust RS485 transceiver. The SN HVD78 RS485 transceiver emits higher than 2 kilovolt human body standard up to 15 kilowatt. But more important, it also meets higher ESD current per the IEC 61000-4-2 with up to 12 kilovolt contact discharge.

We can draw from the data sheet that the IEC at least pass the EDS IEC 61000-4-2 with acceptance criterion C, no hardware destruction and the part works as expected after a test, but won't specify pass criteria A or B as this would require testing in an [INAUDIBLE] system. How does the actual schematics for an RS485 interface benefit from these parameters?

Here, you can see the TIDA 00179 4-wire interface for the data plus and data minus example schematics. The SN65HVD78 [INAUDIBLE] RS485 transceiver with built in IEC ESD protection, as shown on the previous slide, has been chosen. For better noise immunity, the transceiver has a high receiver hysteresis of plus minus 80 millivolt.

Bypass capacitors are added for f transient common mode voltage rejection, and a 10 ohm pulse prove resistors are added to limit the clamping current into the transceiver during over voltage transience. Due to the SN HVD78 built in IEC 61000-4-2- ESD protection, no additional ESD or TVS diet are required when used with a shielded cable to pass the EMC immunity testing.

Here, you can see a test setup for a fast transient burst with up to 4 kilovolt transient bursts. The TI design TIDA 00179 is connected [INAUDIBLE] AM 437x, which runs the [INAUDIBLE] at 8 megahertz and reads a new position at every 16 kilowatts rate. It reports any CRC error for [INAUDIBLE] comport to the PC.

A [INAUDIBLE] 2.2 encoder is connected to a 30 meter shielded cable. The capacitive clamp is one meter length, and the encoder cable is fed through this capacitive coupling clamp. The return current flows through the metal plate below the capacitive clamp.

A decoupling ferrite for the encoder was used, as it's not the device under test. The EFT generator is not shown on that picture. How do the test results look like? The TI design TIDA 00179 was tested for ESD EFT search and conducted RF with levels and performance accepted criterion according to the IED 61800-3 as shown in this table.

Let's have a look at the test results. We can see that the TI design exceeds the IED requirements by passing twice the required voltage. Also note, we passed search without any CRC error and specified EFT and ESD category B already on the occurrence of a single CRC error. How to protect ICs which won't have integrated ESD protection or require increased ESD voltage level protection?

The picture on the left show the protection of a USB interface used for example as a service and maintenance port in a drive where the TPD 4S214 provides [INAUDIBLE] overvoltage, overcurrent protection, and a four channel ESD clamp. ESD protection devices for other interfaces like or ethernet are shown here as well.

For more details, please visit www.ti.com/esd. In the next chapter, we will look into EMI and provide a system example for an EMC and EMI compliant dual port gigabit ethernet design.