Engine controller for space applications


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Microchip Technology has announced a radiation-reinforced mixed-signal drive controller that belongs to the Space System Manager (SSM) product family. Space and weight are always a challenge in space missions. With this new product, Microchip strengthens its portfolio by introducing the new LX7720 controller. The new LX7720 provides a robot control solution for multi-axis pointing mechanisms and precise control of the movement of optical elements. It reduces the number of external components, which reduces the risk of potential electricity to the space environment. At the same time, reducing the BOM reduces the weight of the devices, which is always a problem in space missions. The LX7720 provides four metal oxide half-bridge metal oxide field effect transistor (MOSFET) drivers, four floating differential current sensors, a pulse rate analyzer transformer motor, and all control electronics. The space environment puts the solar wind, cosmic rays and Van Allen bands electronic circuits to the test. These radiations consist mainly of electrons, protons, neutrons, positrons, photons and other particles with ionizing power, capable of breaking covalent bonds between atoms. Damage to transistors is caused by ionization, both field-effect transistors (such as MOSFET) and bipolar junction transistors (BJT). In the case of seasonal transistors, ionization occurs due to the charged particles affecting silicon dioxide (the insulating layer); They induce breaking of electron-hole pairs by directing them toward the silicon oxide interface where they create “trap” states that reduce the number of effective carriers and thus the threshold voltage of the transistor. In BJT, instead, these particles increase the base current and, consequently, the overall gain decreases. The mechanism underlying each single-event effect (SEE) consists in the accumulation of charge in the sensitive region of the device after the passage of the particle. A column of an electron-hole pair with diameters ranging from a few hundred nanometers to a few microns is released along the path by the Columbian reaction in a semiconductor device. Depending on several factors, the particles may cause unnoticed effects, transient disturbances in microprocessor circuit operations, changes in logic states (SEU, SEL), or permanent damage to the device or integrated circuit (SEGR, SEBO). In recent years, changes have combined in several factors to reduce the cost of accessing space. LEO miniature satellites have provided useful data for a variety of scientific missions. Electronic systems in space must withstand extreme temperatures and related thermal cycles, which expose integrated circuits and their beams to mechanical stress. However, a new class of space-based plastic integrated circuits could provide advantages in terms of cost and size over traditional “space-based” components for low-altitude missions. Motion control spacecraft rely on electric motors for important functions such as position control, deployment mechanisms and ultra-precise movements. In these applications, electric motors should have a long service life and high reliability in high vacuum, irradiance, and high operating temperature environments. Both permanent magnet synchronous motors (PMSM) and small stepper motors can be used. Stepper motors do not need the computationally intense PI control loop that a PMSM needs to implement a field oriented or other control system, but have worse acceleration / deceleration and absolute torque performance. In space applications, the highest level of reliability is required, as it is not possible to repair or recalibrate after satellite launch except for certain working conditions. By digitally controlling the motors, it is possible to implement sophisticated fault detection algorithms to improve the performance and, accordingly, the useful life of the motors. Through digital control, it is possible to reduce the energy consumption generated by the satellite’s solar panels or the energy stored in its batteries. Microchip highlights how the LX7720 works with conventional NMOS drive transistors up to 40kHz PWM and motor current measurements in a 12-bit soccer field (with Sigma-delta ADCs, there is a direct trade-off between latency and precision). As FPGAs run at increasingly higher frequencies (Microchip’s RT PolarFire┬« FPGA’s math blocks run up to 450MHz), the frequencies move to increase accuracy. It is possible to end up with PWMs in the 200 kHz + range by using GHz + clocks to achieve 12-bit + resolution with GaN FETs as power transistors. Spacecraft electronics engineers like to implement high-side current-sensing resistors and measure bidirectional current in / out of each winding at the drive end as a low-cost, compact, trouble-free approach when operating over a temperature range of 180 ┬░ C. This requires the LX7720 to include floating differential amplifiers to measure sensing voltage and work well with brushless DC motors and stepper motors. Other current sense techniques, such as the sense transducers, are also good, as you end up with an effort to acquire it. Figure 1: A typical engine operating system with the LX7720 (Source: Microchip) Satellite and other space instrument systems have many applications for engine control. These applications include precise control of the movement of mirrors and lenses also used in scientific research. With rotation and position detection, the LX7720 provides servo motor drive and linear actuator control for brushless DC motors (BLDC), permanent magnet synchronous motors (PMSM) and other motors most commonly used in space. LX7720 is MIL-PRF-38535 Class V and Class Q certified. The LX7720 provides radiation tolerance of up to 100 krad of TID (total ionization dose) and up to 50 krad of lowest single event exposure rate (ELDRS, enhanced low dose rate sensitivity). .


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