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Evaluating High Reliability SMD-0.5 MOSFETs With LX7720 Spacecraft Motor Drivers

This blog post discusses our recently released JANSR N-channel MOSFET family with the SMD-0.5 hermetic package and introduces the LX7720MLF-EVB motor controller evaluation board. This new evaluation board allows SMD-0.5 MOSFETs to be fitted and evaluated, helping designers to optimize their high-reliability motor control circuit designs.

Introduction to High-Reliability Power MOSFETs for Space Applications

As space system developers continually work to reduce the size, weight and power of key modules and elements, they also require higher-performance, radiation-hardened and radiation-tolerant components that enhance system designs. New technology—such as lighter, more highly integrated motor control circuits for satellites—can withstand extreme space environments and optimize spacecraft performance.

The LX7720 spacecraft motor driver is radiation hardened by design. It’s a companion Integrated Circuit (IC) to a space Field Programmable Gate Array (FPGA) such as Microchip’s RTG4™ FPGA and RT PolarFire® FPGA, or a space microcontroller (MCU) such as Microchip’s SAMRH71F20 or SAMRH707F18. The integrated current sensing, resolver, encoder and Hall effect encoder interfaces in the LX7720 reduce board space and weight while increasing reliability for closed-loop motor control using coil current feedback and rotor position sensing.

Microchip's new JANSR N-channel Metal Oxide Silicon Field Effect Transistors (MOSFETs) (MIL-PRF-19500/746) are manufactured at our Colorado Springs facility in North America. The range currently offers four parts from JANSR2N7587U3 (100V VDS) to JANSR2N7593U3 (250V VDS). This MOSFET family exceeds 100 krad TID to target rigorous GEO and MEO missions with the SMD-0.5 hermetic package. Plastic packaging is also planned to reduce cost for LEO and New Space applications.

Figure 1. SMD-0.5 Hermetic Power MOSFET Product Range

Figure 2. SMD-0.5 Hermetic Power MOSFET Package

The new LX7720MLF-EVB motor controller evaluation board supports the common plastic DPAK surface mount power MOSFET package. The eight NFETs fitted as standard for the LX7720's four half-bridges are IRFR3410TRPBF (100V, 31A, 39mΩ max @ VGS=10V) in DPAK, mounted on the Printed Circuit Board (PCB) topside.

The PCB includes eight parallel footprints for the SMD-0.5 package on the underside to allow the high-reliability NFETs to be evaluated directly. The parallel components comprise eight NFETs and eight gate-source resistors (typically 10kΩ) for the four half-bridges as shown below.

Figure 3. Fitment of SMD-0.5 NFETs and Gate Resistors on LX7720MLF-EVB PCB Underside

For each substitute SMD-0.5 half-bridge, the corresponding DPAK half-bridge needs to be disabled. This is done by removing 0Ω resistors which connect DPAK NFETs to their gate drivers. There is a 10kΩ gate-source resistor connected to each DPAK to ensure that any disconnected NFET remains safely off.

You should now understand how to evaluate an LX7720 with space qualified half-bridge MOSFETs in your design. Learn more about the LX7720 and other radiation-hardened mixed signal ICs at our web page.

Tags/Keywords: Aero-Defense

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