Powering CMTI with Current Sensing

Server systems and industrial applications rely heavily on Isolated power supply systems.

Increasingly, these applications demand maximum bandwidth in smaller and smaller form factors. Today, the holy grail is maximizing power per volume (W/mm3).

To achieve this, the requirement is for high performance power switches, capable of switching hundreds of volts in nano-seconds.


Common-Mode Transient Immunity (CMTI)is the ability of a device to withstand common mode transients – voltage spikes that occur on the positive and negative sides of a power supply. (These spikes can be caused by power line fluctuations, lightning strikes, and switching transients from other devices.)

High CMTI  or dv/dt immunity is critical as it ensures the current sensor can accurately measure current even in the presence of high-frequency transient noise. A high dv/dt immunity sensor will be less likely to be affected by transients, and will therefore produce more accurate readings.

And that’s important, because fast switching power systems are noisy. Power supplies often operate in environments with high levels of electromagnetic interference, which can cause erroneous readings, reducing system efficiency and leading to system damage. High CMTI ensures that the power supply will continue to operate correctly even in the presence of common mode transients.

Legacy Solutions

In high dv/dt environments, this ever-present noise becomes problematic to filter out.  Traditionally, solutions have solved for the problem by adding an internal shield. The addition of the shield between the silicon and the frame diverts the noise from the silicon. Unfortunately, this design also reduces the safety isolation performance.

XtremeSense® TMR Technology

Crocus Technology’s family of current sensors – CT417/8, CT427/8, and CT432/3  – all deliver the required high dv/dt immunity. This high CMTI of up to 100 kV/µs makes them ideal for use in applications with high levels of noise and transients.

The high bandwidth, fast response, ultra-low noise, integrated contact current sensors leverage patented XtremeSense® TMR technology to deliver highly accurate current measurements for power applications. They feature optimized package design to minimize coupling between the transients and sensor output without compromising on voltage isolation.

Besides high dv/dt, these contactless sensors feature low input bias current, high input impedance, low noise, and wide operating temperature range. Their consistently high accuracy eliminates false readings, eliminating current protection tripping from inaccurate measurement. And the lack of shield means there’s never an issue with safety isolation performance.

The Crocus Solution

Within the Crocus family, you can choose the ideal amplifier for your application. The CT417/8, CT427/8, and CT433 are all available in package types that make them easy to integrate into a wide range of products.

The CT417/8, CT427/8, are offered as an industry standard a space-saving SOIC-8 package that is “green” and RoHS compliant, reducing the total PCB footprint size up to 8 times smaller compared to existing solutions. The CT432/3 is offered in an industry standard 16-lead SOIC- Wide package that is also “green” and RoHS compliant.

These products directly sense the flow of current through the package avoiding errors in conversion and providing inherently faster and more accurate measurements. With an industry-leading response time of 300 ns, high-power architectures like the CCM Totem-Pole PFC can provide higher power density solutions. 

The fast switching frequency of Wide Bandgap (WBG) power devices requires a current sensor that can detect fast transients to prevent potential cascading failures. The sensors are all available in wide current range (20A to 65A) for 3.3V/5V bias and Bipolar/Unipolar operation.

When it comes to CMTI for power applications, Crocus technology’s family of current sensors are unparalleled in accuracy, reliability, and cost-effectiveness.  Only XtremeSense® TMR technology delivers this ‘no compromise’ solution of high CMTI and safety isolation.


On Key

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