Power-Tip The right integration level for my engine control

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Texas Instruments

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Integrated solutions are becoming increasingly important for developing motor systems more quickly, simplifying component procurement, reducing costs, and realizing a reliable and efficient system. The spectrum here ranges from purely discrete concepts to fully integrated solutions. But which variant is right in each individual case?

According to documents from Texas Instruments.

A motor control contains a microcontroller that generates the control signals for the gate driver from information about the rotor position, and this in turn drives the MOSFETs to power the motor windings.

Such a discretely constructed solution (Image 1), for example, works with bipolar transistors in a totem pole circuit, each driving a MOSFET. While this circuit is easy to implement and cost-effective, a large number of components are necessary that take up a lot of space, especially since several MOSFETs are required for a motor.

An elementary gate driver IC represents a first step towards integration, summarizing the middle part of the circuit (blue dashed line). When looking for the suitable gate driver IC, the number of driver channels must be taken into account as well as the voltage resistance and the current-carrying capacity.

Image 2 illustrates the various variants. There are single-channel gate drivers (e.g., the UCC21732) for driving high- and low-side IGBTs and SiC MOSFETs for voltages up to 700 V and more (used, for example, for AC motors). Dual-channel half-bridge gate drivers like the UCC27712 for driving IGBTs and MOSFETs can be used for motors with operating voltages from 100 to 700 V. Finally, four-channel H-bridges and six-channel gate drivers for three-phase motors like the DRV8329 are also sensible, designed for MOSFETs with rated voltages up to 60 V as well as for DC motors.

The advantage here is that the same design can be used for motors with different power levels, because only the external transistors have to be adapted to the respective voltage and/or current levels.

The three types of gate drivers

The gate drivers themselves can either limit themselves to the basic function or integrate more elaborate protection functions and smart features. While the rise speed is usually determined by external components (two source or sink resistors for current limiting, a diode for individual adjustment of the rise and fall rate, and a pull-down resistor), these components are integrated in smart solutions – including the possibility to specify the edge steepness via SPI interface.

With a six-channel smart gate driver, up to 24 discrete components can be saved for this purpose alone. The component effort is further reduced by integrated protective, fault detection or even isolation functions.

Motor driver ICs go a step further, which contain not only the gate driver but also the FETs, and - as in the case of the DRV8962 - additionally offer protection and diagnostic functions.

As a third option, there are gate driver ICs with integrated control functions that manage without an external microcontroller. These components internally implement the commutation algorithms for trapezoidal, sinusoidal or vector control, for example, without coding effort, which shortens development time and makes debugging and testing less complex.

While the last-mentioned variant works with external FETs, these are already integrated in the fully integrated solution of control, gate driver, and FETs. Such building blocks, which include the MCF8315A, require the least amount of PCB area, but the capabilities of the built-in FETs must be considered, which requires careful calculation of currents and thermal conditions. (kr)