New Small Wheel Low-Voltage Power: Design Review

This document details the present status of research and development for the low-voltage power systems of the ATLAS New Small Wheel (NSW). The combination of large power requirements and low available cabling space suggests a point-of-load conversion archi- tecture, where power is delivered to a front-end board (FEB) at a relatively high voltage (10V or more) and then reduced to the delivery voltage by on-FEB power electronics. This is potentially a multi-step process. Power will be delivered to the rim of the NSW at a voltage of at least 24 V. From the rim, it will be distributed to the individual front-end boards. If the FEBs are unable to directly accept the voltage delivered to the rim, an additional conversion step is required at the point of distribution. This point of distribution is also a natural location for circuit protection and ballast resistors. On the FEBs, power conversion will be accomplished by single-inductor buck converters, optionally followed by one or more low-dropout regulators (LDOs) for noise reduction or to provide additional output voltages. The challenges in this approach are to ensure that the selected power conversion device(s) will: 1. Survive in the radiation and magnetic Field environment of the NSW; 2. Effectively couple to the proposed cooling system; 3. Not introduce noise that may impact sensitive analog components; 4. Fit within the relatively small available space on the FEBs; 5. Allow a cabling solution that fits within the available space for services. This material is written primarily with reference to the MicroMegas, although it is recognized that the chosen solution will likely be adopted by the sTGC detector as well.