Overview
Current is one of the most useful signals in a power design: it tells the controller the torque of a motor, the load on a converter and the state of a battery, and it enables a current limit, a fault detection and a closed-loop control. Measuring it accurately and safely in a high-voltage stage is the challenge, and NOVOSENSE provides the integrated current sensors and the current sense amplifiers that answer it. BeiLuo supplies them with genuine traceability and FAE support. This page shows how they cover the current-sensing role.
The Two Approaches
A current can be measured with a shunt and an amplifier or with an integrated sensor that contains the conductor and the sensing. A shunt gives a simple, low-cost measurement but adds an insertion loss and needs a differential amplifier, and a high-side or a high-voltage measurement needs an isolation. An integrated sensor combines the conductor and the sensing, so the insertion loss is low and the isolation is built in, which suits a high current or a high-side measurement where a direct shunt would be difficult.
Choosing Between Them
Choose the integrated sensor, such as the NOVOSENSE NSM2311, where the current is high and a low impedance and a high capacity matter, and the conductor and the sensing in one module simplify the layout. Choose a shunt and a current sense amplifier, such as the NSCSA240-Q, where a shunt is already in the design and a high accuracy with a good rejection of the switching transient is needed.
The Switching Transient
In a motor drive or a power converter the switching imposes a fast common-mode step on the current sense, and a poor amplifier turns that step into a glitch that corrupts the reading. The NOVOSENSE current sense amplifier is designed to reject that transient, so the current measurement stays accurate in a real power stage, which matters for the control loop and the protection. Confirm the common-mode rejection at the switching frequency on the bench.
Isolation for Safety
The isolation separates the high-voltage current path from the low-voltage signal path, so a high-side or a high-voltage measurement is safe and the logic is protected. Respect the creepage and the clearance on the board and keep the current pins and the signal pins separated, because the isolation is only as good as the layout.
Range and Resolution
Choose the range just above the maximum current you expect, because a lower range gives a higher sensitivity and a better resolution. Distinguish the continuous current from the peak and the inrush: a motor stall current can be several times the running current, so size the range for the stall and accept a coarser resolution at the running point, or add a second sensor for the fine range. Confirm the accuracy at the working current, not only at the full scale.
Accuracy and Temperature
For a demanding design, confirm the accuracy across the temperature range and keep the external magnetic fields and the high-current traces away from the sensor. Calibrate the offset and the gain at the system level where the accuracy budget requires it, and keep the input filter close to the sense point with a Kelvin connection.
Applications and Verification
A current sensor measures the phase current of a motor drive for the control loop and the protection, the output current of a converter for the regulation and the current of a battery for the state of charge and the safety. Validate the design on the bench by measuring the current against a reference across the range, by imposing the switching common-mode step and by checking the accuracy at the temperature extremes. Our FAE team can review the sense design and help you interpret the measurements.
Getting Help
Send your current range, the supply voltage, the isolation and the accuracy you need and the load profile to our FAE team, and we will propose a sensor or an amplifier, help choose the range and the shunt and review the isolation layout. BeiLuo holds mainstream NOVOSENSE sensors in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, so a current-sensing design can move from prototype to production without a supply gap.