SLLA590 May   2022 THVD8000 , THVD8010

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2THVD80x0 Devices Theory of Operation and Limitations of Use
    1. 2.1 Overview and Similarities between Standard RS-485 Transceivers and THVD80xo Devices
    2. 2.2 Differences between Standard RS-485 Transceivers and THVD8000/8010
    3. 2.3 Standard Approach to Using THVD80xo Devices to Communicate over Power Lines
    4. 2.4 Drawbacks to Standard Approach with Higher Voltage Systems
  5. 3Integration of Line Driver with THVD80x0 Devices to Drive Low Impedance Loads
    1. 3.1 Overcoming Drive Strength Requirement with A Line Driver Amplifier
    2. 3.2 Modification to Typical System Signal Chain Path Through Integration of Line Driver
  6. 4High Voltage Interface and Communication Interface Power Supply
    1. 4.1 Line Driver Output and Input RX signal Protection Circuit
    2. 4.2 High-Voltage Interface
    3. 4.3 Receive Path Optional Bandpass
  7. 5System Level View and Relation to Higher Voltage Implementations
    1. 5.1 Powering the Powerline Communication System
    2. 5.2 System Overview with Selected Test Results
    3. 5.3 Changes to Design for Higher Voltage AC or DC Applications
  8. 6Summary
  9. 7References

2.4 Drawbacks to Standard Approach with Higher Voltage Systems

The standard approach works great for lower power systems – but there are two main drawbacks that limit this approach in higher voltage, low impedance applications which are drive strength and circuit protection.

The first major drawback is the drive strength of the circuit. In the standard approach this is handled by ensuring that the inductors total impedance in parallel is equal to or greater than 375 Ω at the OOK modulation frequency. While this is not impossible to meet since the OOK frequency should be much greater than the power signal’s frequency it does require much better inductors as they will need to be able to handle the larger current in high power systems while at the same time have low DCR to ensure as little as attenuation as possible in theses higher power systems. Also, since most of the higher voltage applications are using some frequency (typically 50 Hz – 60 Hz) in the power signal – these inductors will also have frequency related attenuation across the inductors which could be prove problematic from a power delivery standpoint as more attenuation is being added in the line. So, the system complexity can increase due to the lack of drive strength of the THVD8000/8010.

The next drawback is protection. The THVD8000/8010 operates normally with a common mode voltage level of between -7 V and 12 V. These pins can also protect against damage with DC protection up to ±18 V. It is standard practice to add protection diodes to the TVS lines – which works great by themselves in lower power applications. However, they do not react instantly and there is a small frame of time where the device could be exposed to higher voltages. In lower power applications this isn’t a typical concern and a TVS diode is a suitable protection option. When working with voltages at the scale of 110 V AC and higher that reaction time of the diodes may be too long and the THVD8000/8010 will be hit with a high voltage signal and could damage the part. A more robust protection scheme must also be considered if this drawback is to be overcome.

While these drawbacks seem to create many issues with the standard approach, these drawbacks can be overcome with a different approach. Using a few different sub-circuits to increase the drive strength of the THVD8000/8010 as well as offer better protection from the dangerous high voltage signal will allow this device in higher voltage applications.