Why Amplifier and Driver Selection Deserves Care

An isolated amplifier measures a small voltage on the high-voltage side, and an isolated gate driver drives a power switch across a barrier, so their input range, their drive current and their isolation set the accuracy and the reliability of a power stage. Choosing the wrong input range wastes the resolution, and a driver that is too slow or too weak leaves the switch hot. This guide walks through a repeatable method for selecting a NOVOSENSE isolated amplifier and gate driver.

The Isolated Amplifier

An isolated amplifier senses the small differential voltage across a shunt in the high-voltage domain and reproduces it on the low-voltage side with the isolation in between, so a controller can measure the current of a motor phase or a dc bus without a direct connection. The NOVOSENSE parts use a capacitive isolation barrier with a linear differential input and a differential output, which gives a good accuracy and a good rejection of the common-mode noise.

Step 1: Set the Input Range

Choose the input range from the shunt voltage. A ±50 mV range with a small shunt gives a low insertion loss, and a ±250 mV range with a larger shunt gives a better noise margin. Match the shunt and the range so the full current uses the input span without saturating, and keep some headroom for the overload. The shunt tolerance and the amplifier gain together set the overall accuracy.

Step 2: Confirm the Isolation and the Grade

Confirm the isolation rating against the voltage difference and the standard, and choose the automotive grade where the design must meet AEC-Q100, such as a traction inverter or a battery system. The capacitive barrier and the high common-mode transient immunity of the NOVOSENSE family keep the reading accurate when the power stage switches.

The Isolated Gate Driver

An isolated gate driver takes a logic signal from the controller and drives the gate of a power switch across a barrier. The NOVOSENSE NSi6801 sources and sinks a 5 A peak current with a fast propagation delay and a pulse-width distortion of a few tens of nanoseconds, and it provides a high CMTI, so the gate stays clean despite the switching. It is pin-compatible with a popular opto driver, so it is a drop-in upgrade.

Step 3: Choose the Drive and the UVLO

Choose the drive current from the gate charge and the switching speed you need: a larger gate charge or a faster edge needs more peak current, and a 5 A part covers most MOSFET, IGBT and SiC gates. Choose the under-voltage lockout level from the device you drive, so the driver turns on only when the gate supply is high enough to drive the switch fully. Confirm the propagation and the dead-time for the topology.

Step 4: Confirm the Isolation and the Package

Confirm the isolation rating and the package, because a wider body gives more creepage for a higher-voltage system. Provide the required creepage and clearance under the package and keep the gate loop short, because the loop inductance is what turns a fast edge into a ringing gate waveform.

Planning the Layout

The isolated amplifier and the gate driver both sit across a barrier, so the layout must respect it. Keep the input and the shunt close to the amplifier with a Kelvin connection, keep the gate loop short and place the driver close to the gate, provide the creepage under the package, and decouple each side. Measure the common-mode rejection and the gate waveform on the bench at the worst case, and confirm the isolation with a hipot test. Our FAE team can review the layout and the measurements.

Getting Help

If you send your motor and bus voltage, the switching frequency, the current range and the environment to our FAE team, we will propose an amplifier and a driver, help choose the input range and the drive and review the layout. BeiLuo holds mainstream NOVOSENSE amplifiers and drivers in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, and our engineers will review the choice with you before you commit to production.