Crocus Tech – Contactless Current Sensing for Electric Vehicles

Electromobility in the form of electric bicycles or Electric Vehicles (EVs) has gained popularity as gasoline prices increase and the public becomes environmentally aware.  These electromobility vehicles consist of an electric battery for energy storage, an electric motor for movement and a controller to manage the system; all requiring a method for sensing and measuring current. Since the current required to propel an EV can be in the order of 100’s of amps, current measurement can present a challenge for safety, accuracy, and thermal management.

Crocus Technology’s magnetic-field sensors are precisely tailored for use in these high current sensing applications. Crocus’ Tunnel Magneto-Resistive (TMR) technology accurately senses the magnetic field generated by current flowing through a busbar and outputs a proportional voltage that can be directly read by conventional microcontrollers. Sensing a magnetic field makes it possible to measure either DC or AC current. The other advantages of high sensitivity, accuracy, and isolation makes the TMR sensor a better solution than existing current sensing technologies like shunt-resistor or IC Hall-Effect.

When measuring current, it is best to sense near the supply voltage (high-side) instead of near ground (low-side). The advantage of sensing on the high-side is the entire current leaving a battery is measured making it easy to detect any shorts to ground while providing immunity to ground bounce noise not possible with low-side sensing. Using a shunt-resistor for measuring high-side current requires an isolated op-amp which complicates and increases the design cost.  The Crocus TMR magnetic field sensor simplifies the circuit design while providing built-in galvanic isolation. Its construction provides inherent isolation, because the active circuitry on the die does not electrically connect outside of the molded package.

To optimize performance, the CT452/3 placement on the busbar must be considered along with the busbar geometry, Figure 1. The current sensing range can be increased by adjusting the busbar’s cross-sectional dimensions of Length, Width, and Thickness, or by adjusting the distance between the IC sensor and busbar. The spacing distance between the TMR sensors and the busbar is defined as the ‘air gap’, minimizing the air gap will increase the sensing range but will also minimize the voltage isolation.

The CT452/3 PCB can be placed over or under the current carrying busbar and still yield a non-contact and isolated current measurement. Note the busbar top/bottom position relative to the IC will determine the measured current’s polarity.