 Welcome to this presentation on getting to know Solving Stepper Motor Design Challenges with PowerStep01. Let's start with an overview of the PowerStep01. We will first review the PowerStep01 applications, basic control principles, then the key differentiators of the PowerStep01 like the digital motion engine, voltage mode control, current mode control, stall detect, advanced current mode control with PowerStep01, and also system and package integration. Finally, we will go through the evaluation boards that are available. PowerStep01 is ST's most advanced stepper motor driver with some very unique features. PowerStep01 has two H-bridges built in. With two H-bridges, one can drive, by topology, a bi-directional stepper motor, but also one or two brushed DC motors. One brushed DC motor requires one H-bridge if the bi-directional control is required. Stepper motor applications would typically benefit the most from the features and added value of ST's PowerStep01. Typical PowerStep01 applications involve a motor power in the range of 50 watts to 250 watts. It can be used in home automation, ATM and vending machines, industrial applications, printers, robotics, and also medical equipment. Let's check out the benefits and structure of a stepper motor driver. By driving its phases with phase-shifted currents, bipolar stepper motors allow precise angular positioning and provide non-zero torque even when stopped, and thus keep target position fixed. Moving from rectangular phase current wave forms to sine waves, a technique known as microstepping is possible, allowing even more precise positioning. The microstepping technique for stepper motors is based on applying two sinusoidal currents to the motor phases with a phase relation of 90 degrees. Once we apply a sine wave to one phase and a cosine wave form to the other phase, we can align the stator magnetic field in any possible position and direction. A simplified block diagram of the standard current mode control topology looks like the one shown on the picture. The current through the bridge can be sensed on the shunt resistor and is converted into a voltage. The sensing voltage is compared with the reference and the output of this comparator controls the logic and drivers for the power stage. There are also other techniques for sensing the current through the H-bridge. For example, the current from the H-bridge is mirrored or scaled down using a so-called copy-moss. The copy-moss is in parallel to the H-bridge FET and it is used only for the current sensing. Back to microstepping. Here, we'll explain the basic principle of the operation of a stepper motor driver. The digital-to-analog converter generates a voltage reference for the comparator. Of course, it's just an approximation of a sine wave and in reality, we go step by step to various current levels. In other words, the current in the H-bridge is translated into the voltage and compared with the voltage reference. PowerStep01 has a capability of up to 128th microsteps. The number of microsteps is programmable. The red lines depict T on time when the coil of the motor is energized. The blue line depicts the T off time. It means the time when the coil current decays. There are four key differentiators of PowerStep01. Number one, the digital motion engine. Number two, the innovative voltage mode control. Number three, the advanced current mode control. And the last point is the extreme power integration. The digital motion engine is at the heart of the first three key differentiators. The last one is package technology called system in package. We will be talking about the system in package technology at the end of the presentation. The digital motion engine enables the use of smaller microcontrollers or microcontrollers with a lighter architecture. The motor control is provided by high level commands. These positioning or speed profile commands are sent from the microcontroller via the SPI bus. Complex subroutines are already built in the motor driver and there is no need for complex subroutines to run on the microcontroller. We have some more details in the following two slides. To highlight the simplicity of our new PowerStep01 approach, we will first show you a typical topology for more complex applications. As you can see, this requires a lot of different components. That is three stepper motors, the system microcontroller, three dedicated microcontrollers and motor drivers. The system microcontroller controls three dedicated microcontrollers and then each individual microcontroller drives a dedicated stepper driver. A complex subroutine must be developed for the dedicated microcontroller. Moreover, the PCB layout is more complex than the solution with a digital motion engine. Here we show you a system with PowerStep01 and as you can see, it is simplified significantly. Not only from the system architecture point of view, but also in terms of PCB layout as we'll see later in this presentation. We no longer need a dedicated microcontroller to perform speed profile and positioning calculations. All high-level commands are already built in in the PowerStep01 thanks to the digital motion engine. The new architecture with the PowerStep01 leads to a lower bill of material, less complex PCB layout and a single microcontroller which can drive more devices at the same time. The communication between the microcontroller and PowerStep01 is handled over the SPI bus. So, how does the digital motion engine work? The microcontroller sends high-level commands through the SPI bus to the digital motion engine and the PowerStep01 generates the motion. Free run command means to run at constant speed. A positioning command moves the motor to a desired position. PowerStep01 generates all of the motion and takes care of all of the control signals for the H-bridges. The digital motion engine embeds fully programmable speed profile boundaries. There are commands like constant speed, absolute positioning, relative positioning, step-clock mode, acceleration, deceleration, maximum speed and minimum speed. Here are more examples of high-level commands. The move command performs a motion of n steps in the selected direction. This command can be performed only when the motor is stopped. The go-to command reaches the target position using the shortest path. This command can be performed only when a motor is stopped or is running at constant speed. The go-to-dure command reaches the target position by moving the motor in the selected direction. This command can be performed again only when the motor is stopped or is running at constant speed. The voltage mode control is the second key differentiator of the PowerStep01 and its digital motion engine. It is an innovative driving technique that achieves a very smooth motion, superior position accuracy and silent operation. Let's say a few words about the voltage mode control scheme. The voltage mode is based on the linear model of stepper motors. If a voltage sine wave is applied to a stepper motor phase, the resulting current is sinusoidal too. Now, here is a question in which everybody is probably interested. Which one is better? Current mode versus voltage mode. Which one should I choose? In current mode control, fast current changes cause mechanical vibrations. Furthermore, current mode tries to follow a non-ideal profile due to reference quantization and sampling, which translates into noise and jerky motion. The peak current is controlled, and the result is that the average current value is different from the target. This leads to inaccurate positioning. The voltage mode scheme reduces mechanical vibrations due to smooth current transients. Compared to the peak current control scheme, the average current is controlled, and the positioning is very accurate, achieving true microstepping. The switching frequency is constant, and the torque ripple is under control. Let's now consider a few drawbacks of voltage mode control and how PowerStep01 takes care of solving each one of them. First point. Back EMF heavily influences voltage-to-current relation. The PowerStep01 has an effective and flexible back EMF compensation system. Secondly, winding applied voltages are perturbed by supply voltage fluctuations. The PowerStep01 has supply voltage compensation through an integrated 5-bit analog-to-digital converter. Thirdly, phase resistances vary with temperature. The PowerStep01 allows the use of the register to change the phase resistance using a compensation. As you may know, with no back EMF compensation, the net voltage in the phases would be quickly reduced to zero, and hence no current would flow. The motor would have zero torque and stall. Thanks to the back EMF compensation, the current is stable and the torque is constant. Stepper motor motion is not uniform, and this behavior can make the mechanics resonate. When this occurs, the back EMF voltage is no longer sinusoidal, which causes issues in the control algorithm. There are a few strategies which can be used to avoid the motor resonances. For example, we can apply a mechanical load to the motor, and as a consequence, the load shifts the resonance of the system. Another technique is to increase the speed of the motor because the resonance speed is in a limited range. By using the motor inertia and higher acceleration value, the system can move away from the resonance. Voltage mode control allows us to use sensorless stall detection. How does it work? Since in voltage mode control, we control the voltage applied to the phases. We can now monitor the phase current. During normal operation, the amplitude of the phase current is below the stall detect threshold. We also monitor the back EMF voltage amplitude. If the motor stalls, what happens? In a stall condition, the amplitude in the phase current suddenly increases significantly and is now above the stall detect threshold, and the back EMF goes to zero. Those two factors show that the motor stalls. Let's see the advantages of voltage mode versus current mode control. In voltage mode, the power step 01 allows true 128 microsteps, which lead to outstanding smoothness at low speed. It allows sensorless stall detection, and there is no need for a shunt resistor. On the other hand, current mode offers better control of the torque at high speed and is less sensitive to vibration. Let's now present how the digital motion engine can introduce innovative driving techniques and advantages also in the traditional current mode control. We will describe first the adaptive decay and second the predictive current control and how these advanced control techniques allow low ripple and vibration reduction, silent motion, superior smoothness, and more precise positioning. Again, this is made possible by ST's digital motion engine used in our advanced motor drivers. Predictive current control and adaptive decay are ST patents. Decay principle comes from a simple equation. v equals l multiplied by di over dt. The higher the voltage is, the faster the decrease of the energy in the inductances. This is called fast decay. The slow decay definition is, the lower the voltage is, the slower the decrease of the energy in the inductances. Let's look at the peak current control more in detail. The shunt resistor is for illustrative purposes only because power step 01 in current mode features a non-dissipative current sensing and PWM techniques in order to implement a feedback control of current in each of two phases. At power up, the phase current I phase rises in a given direction according to the motor electrical characteristics, the green curve. When the I peak current level is reached, which is indicated by VREF level on R shunt resistor, the starting phase is over and a decay is applied. The recirculation of the phase current occurs only in high side or low side switches of the H bridge. The current is reduced only using the RI discharge. During slow decay, the current ripple is lower than in the fast decay which leads to lower noise and lower power dissipation. The disadvantage of the slow decay is that sometimes the decrease ratio may not be sufficient. After the decay phase, which is timed by fixed T off time, the current will rise again during on time. The peak of the current is sensed again. The next phase will be fast decay. During fast decay, a supply voltage is applied in a reversed polarity. This brings more effective control but at the cost of higher current ripple, higher noise and power dissipation. An efficient strategy to get the right decay mode has to be adopted by the control algorithm in order to achieve accurate control for the desired current profile. The current control algorithm includes continuous selection of the right decay and setting its actual duration. The current control in PowerStep01 is realized by the predictive current control. We'll discuss this algorithm shortly. The traditional current mode control method is based on sensing the peak current through an overcurrent detection. This causes an error in motor positioning. The switching frequency varies as well. On the other hand, the ST predictive current control predicts the extra on time to ensure the average current is achieved, the red dotted line. This leads to more accurate motor positioning and keeps the switching frequency under control. The extra T on time is evaluated cycle by cycle. PowerStep01 autonomously decides the best decay mode and decides the best algorithm. At a normal or stable conditions, the slow decay is applied as much as possible to ensure control stability. Fast decay is used only when necessary or to guarantee the control stability. Mixed decay, a combination of slow and fast decay, is used in quasi-stable conditions. This strategy maintains self-reliant operations, under control, the overall noise is lowered, and ensures a stable system. The fourth key differentiator of PowerStep01 is the extreme power density made possible by advanced system and package technique. On the left side, a typical architecture for the driver plus eight external FETs for two full H-bridge topologies. A multi-island package is used to accommodate the controller and eight external FETs for two complete full bridges. They are integrated in a single QFN package, 14 mm by 11 mm, with a maximum thickness of 1 mm. As a result, a 67% board area reduction is achieved for superior performance. It reduces bill of material and removes PCB layout issues. Here, on the right, are some more details about the exposed pads on the bottom of the power system and package, showing the output of the full H-bridges, the supply voltage, and the ground pads. This topology brings superior thermal performance. On the left side, the application schematics of the PowerStep01 are drastically simplified and require only a few external components, summarizing the major features of the PowerStep01 device. The operating voltage is between 7.5 to 85 volts. Dual full bridge with RDS on equals 16 mOhm's maximum output current is 10 amps RMS. The PowerStep01 has adjustable output slew rate, programmable speed profile. It has up to 128th microsteps in voltage mode control, sensorless stall detection, and integrated voltage regulator. The PowerStep01 can be controlled via SPI interface. It has low quiescent standby current, programmable non-dissipative overcurrent protection, and also over-temperature protection. Evaluation boards can be ordered at the URL indicated. The first one is the EVL PowerStep01. Technical documentation, application note, full schematics, and software are available on ST.com to run the evaluation board. For this board, it is required to have an interface board, as mentioned here. Another board is available. The PowerStep01 Nucleo Shield Board, the XNucleo IHM03A1. It is compatible with Nucleo and Arduino boards. It is also very easy to start by using the STM32Cube software. All necessary information and documentations about XNucleo IHM03A1 are available on www.st.com. Thank you for following this e-presentation on PowerStep01. We hope you enjoyed it and found it useful.