Overview
A motor drive or an inverter switches a large current across several power devices, and each gate must be driven with a clean, isolated signal while the current is measured accurately for the control loop. NOVOSENSE provides the isolated gate drivers that drive the gates and the isolated amplifiers that sense the current, so a designer can build a complete isolated power stage. BeiLuo supplies them with genuine traceability and FAE support. This page shows how the drivers and the amplifiers fit together.
The Isolated Gate Drive
In a three-phase inverter the high-side switches float at a potential that follows the output, and the ground of the drive moves quickly, so the gate signal must cross an isolation barrier. A NOVOSENSE isolated gate driver such as the NSi6801 takes a logic signal from the controller and drives the gate with a 5 A peak source and sink current, a fast propagation delay of about 75 ns and a pulse-width distortion of about 30 ns, and it provides a common-mode transient immunity of at least 150 kV/us, so the gate signal stays clean despite the switching. The driver side runs up to 32 V with an under-voltage lockout, and the part is pin-compatible with a popular opto-coupled driver, so it is a drop-in upgrade.
Why Not an Opto Driver
An opto-coupled gate driver uses an LED that ages and dims, and it radiates more than a capacitive isolator. The NOVOSENSE capacitive driver has no LED to age, so its life is longer, and its low radiated emission and high CMTI suit a fast power stage better. For a new design or a replacement, it is the cleaner choice.
The Isolated Current Sense
The control loop and the protection both need an accurate current, and in a high-voltage stage the current is best measured with an isolated amplifier. A NOVOSENSE isolated amplifier such as the NSI1300 senses the small differential voltage across a shunt on the high-voltage side and reproduces it on the low-voltage side with the isolation in between, with a differential output for a good rejection of the common-mode noise. The capacitive barrier gives the high CMTI that keeps the reading accurate when the power stage switches.
Choosing the Shunt and the Range
Choose the shunt and the input range together: a small shunt with the ±50 mV range gives a low insertion loss, and a larger shunt with the ±250 mV range gives a better noise margin. Match the two so the full current uses the input span without saturating, and keep the shunt and the input filter close to the amplifier with a Kelvin connection.
An Automotive Power Stage
For an electric-vehicle traction inverter the same chain must also meet the automotive requirement, so the designer chooses the AEC-Q100 parts, such as the NSI1311-Q1 isolated amplifier and a qualified gate driver, and confirms the qualification and the temperature range for the application. The NOVOSENSE parts share the isolation technology, so the design is consistent across the automotive and the industrial versions.
Thermal and EMC
A motor drive runs hot and switches hard, so the driver and the amplifier must be placed close to the power stage with a good thermal path, and the isolated supply and the gate loop must be kept short. The high CMTI of the parts helps, but the layout still decides the result, so keep the loops small and the barriers clean.
Verification
Validate the design on the bench by checking the gate waveform at the worst-case current and frequency, by measuring the current-sense accuracy at the worst-case common-mode step and by confirming the isolation and the creepage. Our FAE team can review the gate drive and the sense design and help you interpret the measurements.
Getting Help
Send your motor and bus voltage, the switching frequency, the control method and the environment to our FAE team, and we will propose a gate driver and an isolated amplifier, help choose the drive and the shunt and review the layout. BeiLuo holds mainstream NOVOSENSE drivers and amplifiers in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, so a motor drive design can move from prototype to production without a supply gap.