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Description
This paper describes a new kind of volage clamp IC combining precise regulation with high current capability and it's various application use cases. Special attention is given to thermal design limitations.
The evolution of power distribution in spacecraft goes into direction of modular architecture. Especially the secondary power distribution from the satellite bus to the local consumers can be made more efficient, reliable and failure-tolerant by applying modular design. Such architecture comprises distributed power conversion, which on the other hand makes necessary a distributed voltage protection to safely keep every local supply voltage below the maximum rating of the load. Power lines in modern spaceborne devices are exposed to many potentially harmful events, including consequences of short circuits and single event effects in DC/DC converters. Once a failure occurred, it can further propagate through the architecture. Small voltage protection circuit at the proper place can limit or even prevent such failure propagation.
The voltage protection circuits can be realised using the described small and easy applicable voltage clamp IC. It is a fast and precise adjustable shunt voltage regulator with high current capability and integrated voltage reference. Additionally, the proposed circuit can be used in a variety of other popular applications (see attachment).
The device consists of internal housekeeping block, error amplifier, high-voltage power switch and monitoring block. The device operates in two primary modes: standby and regulation. Only internal housekeeping and the main regulation loop are powered up in standby mode to achieve a supply current consumption of 120 μA (typical). Power-hungry monitoring circuitry is activated only after the detection of an overvoltage event on the protected rail. The device generates “Active” signal if activated, as well as “Alert” signal in case of overvoltage, overtemperature or power transistor overcurrent.
The separation of VCC supply pin and VCL power switch output allows clamping voltage setting as low as 800 mV, while VCC has to be in the range of 3...40 V. The power switch is capable of handling 10 A pulse current with appropriate heating limitations. An external resistor can help dissipating more power and dealing with higher current-voltage product.
Radiation hardening of the device was an integral part of the design process. The fully isolated SOI technology and factory-provided data on total dose behaviour of 1.8 V devices, enclosed layout 3.3 V and LDMOS transistors as well as latchup-immune 1.8 V standard cell library are the foundation, on top of which digital, analogue and power IPs protected against total dose, latchup and single event effects were designed. The protection means for digital signals include triple-mode redundancy and filtering against single event effects and full dielectric isolation of nMOS and pMOS transistors against latchup and inter-transistor leakages. Each analogue node was also protected accordingly to circuit specifics by common topology measures including cascoding to reduce drain-source voltages, reference voltage filtering, static current definition to override SETs, and so on. Various methods of SET-induced current isolation or sharing were used on the layout level. The final design was extensively tested by current injection to ensure single event transient robustness, which is especially important in a device comprising a low-ohmic power switch. The design targets a TID tolerance of 100 krad(Si) and SEE insensitivity for LET up to 60 MeV*cm2/mg.
The design of active adjustable voltage clamp is presented. The proposed device is able to protect power lines from overvoltage event and can also work as a shunt regulator. The device utilises fully isolated SOI technology and methods of radiation hardening by design.
