Introduction

A Fuji Electric IPM brings the power stage, the gate drive and the protection together in one package, which simplifies the drive design but still leaves several decisions to the designer: the control supply, the current-sense resistor, the protection thresholds and, where required, the brake chopper. This application note explains those decisions for compact inverter, HVAC and servo drives, so a design moves quickly from concept to a reliable board.

Control Supply and Interface

A Fuji IPM is designed to be driven directly by a microcontroller. It uses a single 15 V control supply and accepts a 3.3 V or 5 V logic input, so it connects without level shifting. The control supply must be clean and well decoupled close to the module, because noise on the supply can disturb the gate drivers. The module's undervoltage-lockout protection shuts down the output if the supply sags below its threshold, then clears automatically when the supply recovers, which protects the silicon from the weak gate drive that a low supply would cause.

Input Logic and Dead Time

Inside the IPM, the dead time between the high-side and low-side switches is fixed and factory-tuned, so the designer does not generate it in software. This removes a common source of shoot-through failures in discrete designs and simplifies the microcontroller code. The input signals still need to respect the module's minimum pulse timing, so check the datasheet for the switching timing and the propagation delay before finalizing the control loop.

Overcurrent Protection

An IPM detects overcurrent by sensing the current through the low-side switches. The designer selects an external current-sense resistor that sets the trip level. Size the resistor so the trip current sits above the motor's peak operating current with margin, but below the module's safe limit. A trip that is too low nuisance-trips on normal acceleration; a trip that is too high does not protect the module. After a trip, the module outputs an alarm for a defined hold time and latches off until the fault is cleared, so the controller should read the alarm and shut down the motor cleanly before re-enabling.

Short-Circuit Protection

A short circuit produces a much faster current rise than an overload, so short-circuit protection must act in microseconds. The IPM's dedicated short-circuit protection turns the output off quickly to limit the fault current, protecting both the module and the motor winding. Because the energy in a short circuit is limited only by the loop inductance and the DC-link voltage, keep the power loop small and use an appropriately rated DC-link capacitor.

Undervoltage and Overtemperature

Undervoltage lockout protects against a sagging control supply, and overtemperature protection monitors the module temperature and shuts down if it exceeds a safe threshold, typically around 175 C for the X series. Both faults assert the alarm output with their own hold times. The controller should treat the overtemperature alarm as a warning to reduce load or improve cooling, and the undervoltage alarm as a supply problem to investigate.

Alarm Hold Times

Each fault type asserts the alarm for a specified hold time. The controller must sample the alarm fast enough to catch the shortest of them and must not re-enable the drive until the fault has cleared and the load is safe. Documenting these times in the control software prevents nuisance restarts and protects the hardware.

The Brake Chopper

Some Fuji IPM versions include a brake chopper, which lets a drive dump regenerative energy into an external brake resistor. This matters for loads that must stop quickly or hold position, such as a servo axis or a washing-machine drum. The chopper switches the resistor across the DC link when the bus voltage rises above a threshold, dissipating the excess energy. Size the resistor from the regenerative energy per stop and the desired stopping time, and check its power rating against the duty cycle. A single emergency stop needs far less resistor than a machine that brakes every few seconds.

Thermal and Board Layout

Even with integrated protection, thermal design and layout decide reliability. Mount the IPM flat against a clean, flat heatsink with a thin, uniform interface, and verify the case temperature at full load. Keep the DC-link capacitor close to the module power terminals to minimize the commutation loop, route the sense resistor with short leads, and keep high-current paths away from the low-level control signals. These habits keep EMI low and the protection reliable.

Conclusion

A Fuji Electric IPM removes most of the power-stage engineering from the designer's task, leaving the control supply, the trip level and the brake resistor to specify. Get those right, respect the layout and thermal rules, and the result is a compact, reliable drive that reaches production quickly.