Reinforced Isolation: Safety for your Electronic Designs
Christine Halsey posted on February 05, 2015 | | 18172 views

Texas Instruments has sponsored the following story

Designing Safe Electrical Equipment with Isolation
Isolation is key to designing safe electrical equipment. From Biomedical to Industrial applications, engineers must protect the end equipment and users from high-voltage sources.

Not only does proper isolation block hazardous voltages from humans, equipment, and other electronics, it can also have a functional element such as in solar arrays, eliminating the noise in high speed switching in power conditioning applications, and motor drive circuits.

However, selecting the proper isolation for your design depends on several parameters. Engineers must assess where the device will be located, how it will be used, and the safety regulations that govern the necessary layers of isolation. Texas Instruments (TI), has a series of isolation options that can ensure a product's regulatory compliance.

Insulation Classes for Electrical Isolation

Series-capacitor isolation barrier.
Isolation is typically achieved using one of four insulation classes.

The first class is purely functional; it is required for the proper operation of the design such as level shifting low-voltage control signals to high-voltage DC buses. The next class is basic insulation which is a device with a regulation-based minimum isolation barrier strength, provided by digital isolators or optocouplers. Safety standards state that these basic insulators must be supplemented with another basic-equivalent or supplemental passive barrier to protect any human-machine interface in the case of failures. This third class of insulation is called double insulation.

The final category of insulation is reinforced isolation. Reinforced isolation is widely used in high-voltage systems because it combines the equivalent of double isolation into one barrier. The isolated sensing systems that reinforced isolation provides can reduce power consumption and increase efficiency due to their high-precision, and isolated front-ends optimized for power-consumption.

Isolation Options for Electrical Engineers

TIDA-00171 - Isolated Current Shunt and
Voltage Measurement Design
The TIDA-00171 is an evaluation kit and reference design that implements reinforced isolation technology.

The kit is well suited for AC motors, UPS's (Uninterruptible Power Supplies), and Solar Inverters. This is because TIDA-00171 can monitor up to 7 power lines; three currents, three voltages and the DC Link voltage.

Instead of the traditional Hall Effect sensors, or current shunt sensors with opto isolators, TIDA-00171 uses the AMC130x family of reinforced isolated delta-sigma modulators. The kit also employs integrated Sinc filters in the C2000™ TMS320F28377D Delfino™ microcontroller.

To improve the configuration and implementation of the TIDA-00171, firmware is included. This firmware allows users to configure the filters, adjust the internal PLL frequency and receive data from the filters. Additionally, a user-friendly GUI is included for complete performance analysis.

TIDA-00330 - Reinforced Isolated
M-LVDS Transceiver
To implement AC motor & inverter drives, PLCs and any high-speed capable isolated industrial or automotive data link, the TIDA-00330 is a good reference design option. It combines the reinforced isolation of the ISO7842 and the SN65MLVD203 M-LVDS transceiver.

The ISO7842 uses capacitor-based isolation and a silicon-dioxide dielectric to provide a quad-channel high-speed (100Mbps) isolator. The ISO7842 gives the TIDA-00330 design a lot of versatility due to the isolation's high-voltage performance and reliability.

The SN65MLVD203 allows the TIDA-00330 to perform full-duplex M-LVDS (Multi-point Low-voltage Differential Signaling). The combination is capable of speeds up to 100Mbps. This allows the design to achieve differential signaling standards and high data rates over long distances while using a low amount of power.

TIDA-00267 - Polarity Correcting
Isolated CAN
If your design requires making an isolated Controller Area Network (CAN) bus independent of polarity then you might need TI's TIDA-00267. The design is made possible by combining the ISO7842 with the TPS22968 and 2 of TI's flagship CAN transceivers.

The TPS22968 is a 2-Channel Load Switch with features like controlled turn ON and quick output discharge. The load switch was used as a power multiplexer in this case for an efficient solution that delivered optimal BOM, routing and area usage. The TIDA-00267 design also uses two CAN transceivers, SN65HVD255, to allow for highly loaded networks. This design not only provides an excellent level of isolation but also helps solve the problem of improper polarity installation by customers.

TIDA-00080 - Isolated Shunt based Current
Sensing Module with Delta-Sigma Modulators
The TIDA-00080 is a good option when insulating power protection circuits such as protective relays, IEDs (Intelligent Electronic Devices), and polyphase shunt based energy meters.

TIDA-00080 uses shunt based current measurement. This eliminates the need for current transformers. Therefore, engineers can reduce board size, weight and mechanical issues with this design.

The TIDA-00080 employs the AMC1304, which incorporates both high voltage isolation, and six Delta-Sigma Modulators. There are three individually isolated channels for monitoring current and three channels that share an isolated power supply for monitoring voltage. The design also employs a Digital Filter Board with three programmable PLLs (Phase Lock Loops).

To simplify the integration of TIDA-00080 into your design, it is packaged with a LabView based GUI. This interface can be used to analyze and test the product. Additionally, the GUI gives designers the ability to capture and store samples in a .CSV file which is easily imported into Excel.

TIPD-165 - Isolated, Shunt-Based Current
Sensing Design
The TIPD-165 is another isolated, shunt-based, current sensing design that pairs the AMC1304M25, an isolated delta-sigma modulator, with the TMS320F28377D microcontroller.

The TIPD-165 design is ideal for current measurement applications that require galvanic isolation. For example, this galvanic isolation could include industrial motor drives, photovoltaic inverters, and energy metering.

Without calibration, the TIPD-165 can measure DC and AC load currents in the range of ±10A and an accuracy of 0.3% or better. The flexibility of this reference design allows also evaluation of higher current ranges by choosing different shunt resistor values. In this way it can be easily plugged in to existing systems.

The last thing you want to happen as an engineer is to find that your design failed to prevent hazardous voltages from reaching the protected side. Standards for reinforced isolation are stringent and TI's line of products ensures your design meets or surpasses these criteria. Additionally, TI's offers how-to's schematics, and block diagrams to help designers select components, measure results, test data, and implement their designs.

Texas Instruments has sponsored this post. They have no editorial input to this post - all opinions are mine. Christine Halsey



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