motor drive.PNGIsolators are devices that minimize direct current (DC) and unwanted transient currents between two systems or circuits, while allowing data and power transmission between the two. In most applications, in addition to allowing the system to function properly, isolators also act as a barrier against high voltage.


For example, in this motor drive system, the isolated insulated gate bipolar transistor (IGBT) gate drivers level shift low-voltage signals from the control module to IGBT gate-drive controls referenced to the inverter outputs. At the same time, they also form a protective barrier between the high voltage (DC bus, inverter outputs, and input power lines) and the control module, which may have human accessible connectors and interfaces.


In high-voltage applications, failure of the isolation barrier can result in a potential hazard to human operators, or cause damage to sensitive control circuitry leading to further system malfunction. Therefore, it is important to understand what may cause the isolator to fail, both under normal and fault conditions.


Types of Failure Modes

There are two possible failure modes of isolators. The first is when the voltage across the isolation barrier exceeds the isolator’s rated limits. The first is when the voltage across the isolation barrier exceeds the isolator’s rated limits. The second is when circuits or components integrated in the isolator close to the isolation barrier are damaged by a combination of high voltage and high current. Potentially this can cause damage to the isolation barrier. To learn the more about the failure modes of isolators, click here to download the details.


Combating Isolator Failures

The ISO7841x device is a high-performance, quad-channel digital isolator with a 8000-VPK isolation voltage. This device has reinforced isolation certifications according to VDE, CSA, CQC, and TUV. The isolator provides high electromagnetic immunity and low emissions at low-power consumption, while isolating CMOS or LVCMOS digital I/Os. Each isolation channel has a logic input and output buffer separated by a silicon-dioxide (SiO2) insulation barrier.


This device comes with enable pins that can be used to put the respective outputs in high impedance for multi-master driving applications and to reduce power consumption. The ISO7841 device has three forward and one reverse-direction channels. If the input power or signal is lost, the default output is high for the ISO7841 device and low for the ISO7841F device. See the Device Functional Modes section for further details.


Used in conjunction with isolated power supplies, this device helps prevent noise currents on a data bus or other circuits from entering the local ground and interfering with or damaging sensitive circuitry. Through innovative chip design and layout techniques, electromagnetic compatibility of the ISO7841 device has been significantly enhanced to ease system-level ESD, EFT, surge, and emissions compliance. To learn more about the ISO7841X Quad-Channel Digital Isolator, click here.