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Radiation-Hardened Mixed Signal Motor Controller

The need to reduce size, weight and power (SWaP) on satellites and other space systems continues to challenge the aerospace market. Combining more than 20 commonly used functions into a single chip, Microchip Technology Inc. has announced the LX7720 radiation-hardened mixed signal motor controller, the latest addition to its Space System Manager (SSM) product family. As the industry’s first highly integrated radiation-hardened by design (RHBD) motor control integrated circuit (IC), the LX7720 significantly reduces weight and board space relative to conventional discrete motor control circuits. By reducing the number of components on a system, developers can inspect and test fewer parts, while also minimising the physical points of potential failure due to a smaller number of connections and solder joints.

The LX7720 provides four half-bridge drivers with floating current sense for motor coil driving, six bi-level inputs for sensing rotary encoders, and a resolver to digital interface with primary coil driver. When used with an FPGA, the LX7720 provides a complete closed loop motor driver with coil current feedback and rotation or linear position sensing. With flexible FPGA programming, the combined system can provide motor control for Stepper motors, Brushless DC and Permanent Magnet motors. Position sensing supports encoders, Hall sensors, resolvers, synchros, and LVDTs. FPGA IP modules are available to support motor driving functions from open loop cardinal step driving to space vector modulation using field oriented control. The LX7720 contains 7 sigma delta modulators for analog sampling; the sinc3 filters and decimation is performed in the FPGA with available IP module. Four of the modulators sample the voltage across floating current sense inputs and three modulators sample differential analog inputs such as the outputs of a resolver transformer. Speed versus accuracy tradeoffs can be exploited.

The LX7720 supports a ground potential difference between the motor and signal grounds of up to 10V and motor supply voltages up to 80V. Resolver carrier frequencies from 360Hz to 20kHz are supported. The LX7720 offers 2kV HBM ESD pin protection on all sensor and bi-level pins. It is packaged in a 132 pin ceramic quad flat pack and operates over a -55°C to 125°C temperature range. It is radiation tolerant to 100krad TID and 50krad ELDRs as well as single event latch up immune up to 87.85MeV·cm2/mg and 125°C (fluence of 1e8 particle/cm2).


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