Motor control design made easy
Integrated bridge drivers with diagnosis and protection features
For many actuators in automotive and industrial applications below 500W cost effective DC brush motors are still the motors of choice. On the other hand there is an ongoing transition from relay to PWM driven motors. This enables variable speed applications and more comfort plus higher energy efficiency of the drive. In addition safety, diagnosis and protection of the device are the latest needs for new designs. All these needs can be addressed with integrated bridges like the NovalithIC family, which combines a half bridge with the driver stage, diagnosis, current measurement and MOSFETs in one single package. For a fast and easy path to the next motor control design Infineon offers an Arduino power shield with the highly integrated NovalithIC driver.
There is a clear trend that the distributed loads in cars, such as HVAC blower, engine cooling fan, water and oil pumps, parking brake, front and rear wiper to name a few, driven on energy efficiency are getting smart to provide “power on demand”. In most applications, simple, low-cost DC motors are used, while dynamic DC motor control using PWM improves efficiency, comfort and safety. In a typical fuel pump application fuel savings of >1% compared to a mechanical solution can be realized. For higher power requirements the focus turns to highly efficient and durable brushless DC motors with electronic commutation.
The number of electrical motors in a vehicle increases, due to the fact that belt driven and manual functions are being replaced by electrical controlled motors. Market researchers from IHS counted 2.3 billion electrical automotive motors in 2012 and expect an increase up to 2.9 billion electrical automotive motors in 2017 with a CAGR (Component Annual Growth Rate) of 5.7%. This means an average of 30 motors per car. Today approximately 68% of these motors are DC brushed. The number of brushless DC motors is about 15%, but increasing. In industrial markets the growth rate is even higher (CAGR 6.4%). Furthermore, with billions of motors sold and high annual growth rates home appliance and consumer segments represent high potential markets. Benefits of DC motors are the simple winding and the usage of simple magnets, which enables cheap motors. But the commutator results in larger size and lower lifetime. BLDC motors are more efficient, smaller and show a longer lifetime, but are more expensive.
Integrated bridge driver
Many of the electrical drives are still controlled in a relatively simple on/off way, using relays, linear mode transistors or discrete electronics without diagnostic functions. But there is an ongoing transition to smarter and diagnosis capable motor control designs, mainly driven by improved efficiency and comfort. A typical motor control design consists of a voltage supply, communication interface, microcontroller, control stage, drivers and MOSFETs (Figure 1).
Figure 1: Simplified block diagram of a typical motor control design
There are various integration concepts for combining functional blocks into ICs. A very efficient approach uses drives with integrated motor bridges (Figure 2).
Figure 2: Integrated motor bridges simplify the development efforts
for motor control designs while reducing board space
With this solution a microcontroller permits digital control and advanced diagnostic functions. Monolithic H-bridges or multichip-ICs (Half and/or H-bridges) with integral protection features are used on the load side, which simplifies the development required for controlling the motor. A variety of small unipolar and bipolar drives benefits from this integrated protection concept at the driver side.
Figure 3: NovalithIC with open package showing chip-on-chip
and chip-by-chip construction
The block diagram (figure 3) illustrates a complete low-ohmic-protected half-bridge in a single package. It can be used for unidirectional motor control and – through the combination of two devices – as an H-bridge (bidirectional motor control) as well. The outlined NovalithIC device from Infineon has the capability to switch with a high frequency PWM while providing current limitation functionality, undervoltage and overtemperature protection. This concept offers cost-optimized solutions for protected high-current PWM motor drives with very low board-space consumption and provides the following advantages:
- Very low parasitic inductances between high side and low side MOSFET
- Optimized switching performance of the MOSFETs to reduce power losses and EMC emission
- Drive the motor with PWM for torque and speed control
- Active freewheeling
- Integrated current measurement
- Integrated diagnosis and protection
- Microcontroller-compatible input pins
- Small and PCB-area saving package
Three in one: Ideal for space-constrained applications
The internal 3-chip structure of Infineon’s NovalithIC family comes in a D2Pak (TO-263-7) and comprises a half-bridge driver, an nchannel MOSFET and a p-channel MOSFET in chip-by-chip and chip-on-chip construction (Figure 4). While typically five chips (half-bridge driver and four MOSFETs) are needed, they can be replaced by two devices in a conventional H-bridge application for controlling a bidirectional brushed DC motor. This reduces the component mounting effort and the space saving is in the range of about 30 %.
Figure 4:Block diagram of a NovalithIC with integrated diagnosis functions
and current measurement feature
The NovalithIC devices bring the advantages of particularly compact designs to applications beyond 250W without requiring increased cooling efforts. Integrated features – such as overcurrent protection, undervoltage lockout and overtemperature protection – considerably reduce design work and, at the same time, keep system costs (BOM) at a low level.
Since the integrated driver IC works with a logic level input it can be controlled directly by the microcontroller. Latest p-channel MOSFET technology enables a significant reduction of EME (Electro Magnetic Emissions) and power dissipation thanks to an optimized switching shape and the absence of a charge pump.
Minimum parasitic effects
A common problem in the control of highly dynamic systems, such as PWM-controlled brushed DC motors, is the interference effect due to, for example, parasitic stray inductances in the commutator circuit with capacitor, high-side and low-side switch. Even in a layout optimized with a large amount of design work, negative voltage spikes of 5V and lower can be generated by fast dl/dt rates for a 200W drive. These parasitic effects can be eliminated with integrated designs, in which wire lengths are practically negligible, under comparable conditions voltages of only approximately 1V below ground occur.
Diagnosis and protection included
Diagnostic functions, such as a current measurement are vital for efficient motor control. Designers can decide how much effort to invest in the precision of the current measurement depending on individual application requirements. With the NovalithIC for example, an accuracy of ±10% is possible by a simple end-of-line calibration. The tolerance can be further reduced to ±3% with temperature compensation. Without calibration effort by the user, the device offers a worst-case tolerance of ±28% for current measurements across the nominal output range and across the full range of the operating temperatures.
The bridge drivers use a separate internal current measurement function to detect overcurrent situations and protect the device. If the current through the high or low side MOSFET reaches a specified threshold, the device switches to a defined mode, which results in a controlled limitation of the current in combination with an inductive load (motor).
Finally, protection features ensure high reliability. In this example a temperature sensor is located on the logic chip, which is placed directly on the pchannel MOSFET. Once a critical temperature is reached here (e.g.,Tj > 155°C), the driver switches itself off and goes into tri-state at the output. From there, it can then be actively powered on again by means of a signal from the microcontroller (latched) if the temperature drops at least by the thermal hysteresis of typ. 7K.
Multi-talent: One chip for a wide range of motor control applications
Infineon’s NovalithIC chips meet the AECQ-100 standard and work in a temperature range of up to Tj = 150°C. This makes them suitable in principle for all automotive applications. With the BTN8982TA, for example, an RDS(on) typ. value of 10m? is achieved in the path (high-side and low-side MOSFET combined), and thanks to the excellent thermal performance of the D2PAK, even applications handling more than 250W can be served without significant cooling effort. Concrete application examples include all motor control designs, such as brushed DC (unidirectional and bidirectional) as well as 3-phase brushless motors, in which three NovalithIC chips are used.
Typical examples, which can be found in the automotive sector, are HVAC blowers, sunroof controllers, park brakes, fuel pumps (figure 5) or power-seats. NovalithIC is also the fit for many industrial electronic applications (figure 6) and home appliances: e.g. coffee machines, electrical controlled bed and sun blinds.
Figure 5: Unidirectional motor control, which is used for example
for fuel pump control to save fuel and reduce emissions
Figure 6: Bidirectional motor control for industrial applications
Fast and easy design: with shields for Arduino
Infineon Technologies provides several dedicated shields for the Arduino design community to provide a wider marked access to Infineon semiconductors. Arduino is based on a microcontroller board with a defined form factor and was launched as an open source (hardware and software) platform to enable a fast and easy way to electronic prototype designs. The shields are compatible to Arduino Uno R3 and can be combined with the XMC1100 Boot Kit from Infineon, which is equipped with a 32-bit microcontroller of the XMC1000 family. All XMC1000 products use the ARM® Cortex®-M0 processor.
The DC Motor Control Shield with the NovalithIC BTN8982TA for Arduino (figure 7) enables a fast and cost-effective prototyping of DC motor control designs with easy testing of half-bridge and full-bridge motor control applications. The shield is capable to drive two uni-directional DC motors or one bi-directional DC motor. For this purpose, the shield implements two BTN8982TA fully integrated high-current half-bridge drivers.
Figure 7: DC Motor Control Shield with BTN8982TA for Arduino
The DC Motor Control Shield with BTN8982TA for Arduino is capable to handle high-frequency PWM inputs of, for example, 30kHz. The shield supports brushed DC motor control up to 250W continuous load (i.e. at 12V / 20A) while the BTN8982TA is having a current limitation, which allows nominal currents of up to min. 55A.