A command interface application-specific integrated circuit (ASIC) and an analog interface ASIC have been developed as a chip set for remote actuation and monitoring of a collection of switches, which can be used to control generic loads, pyrotechnic devices, and valves in a high-radiation environment. The command interface ASIC (CIA) can be used alone or in combination with the analog interface ASIC (AIA). Designed primarily for incorporation into spacecraft control systems, they are also suitable for use in high-radiation terrestrial environments (e.g., in nuclear power plants and facilities that process radioactive materials).

The AIA and the Interface between the AIA and the CIA provide ground isolation between the CIA and sides A and B of the I2C bus.
The primary role of the CIA within a spacecraft or other power system is to provide a reconfigurable means of regulating the power bus, actuating all valves, firing all pyrotechnic devices, and controlling the switching of power to all switchable loads. The CIA is a mixed-signal (analog and digital) ASIC that includes an embedded microcontroller with supporting fault-tolerant switch-control and monitoring circuitry that is capable of connecting to a redundant set of interintegrated circuit (I2C) buses. Commands and telemetry requests are communicated to the CIA. Adherence to the I2C bus standard helps to reduce development costs by facilitating the use of previously developed, commercially available components.

The AIA is a mixed-signal ASIC that includes the analog circuitry needed to connect the CIA to a custom higher-powered version of the I2C bus. The higher-powered version is designed to enable operation with bus cables longer than those contemplated in the I2C standard. If there are multiple higher-power I2C-like buses, then there must an AIA between the CIA and each such bus. The AIA includes two identical interface blocks: one for the side-A I2C clock and data buses and the other for the side B buses. All the AIAs on each side are powered from a common power converter module (PCM). Sides A and B of the I2C buses are electrically isolated from each other (see figure). They are also isolated from the CIA by use of transformer coupling of signals between the AIA blocks and the CIA.

This work was done by Baldes Ruiz, Burton Jaffe, Gary Burke, Gerald Lung, Gregory Pixler, Joe Plummer, Sunant Katanyoutanant, and William Whitaker of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Computers/Electronics category.


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Refer to NPO-30275, volume and number of this NASA Tech Briefs issue, and the page number.