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Design of highly-efficient affordable power management circuits in high-voltage 0.35μm technology for automotive applicationsAuthor: Krishna Kanth Gowri Avalur Date: 2018-11-30 Report no: IIIT/TH/2018/81 Advisor:Azeemuddin Syed AbstractEfficient power conversion is an extremely important area of research in modern day electronics.Because of wide range of supply voltages in which the ICs operate, the power conversion or the power management IC (PMIC) needs to work from one voltage range and deliver power at different voltage range. Over the last 20 years, automotive industry has seen a lot of evolution from being a purely mechanical system to an electro-mechanical system. Unlike consumer electronic goods like smartphones, automotive electronics demand high quality, lifetime and durability. Most automobiles available these days run on a 12V battery. The commonly used lead-acid battery when fully charged can exhibit a voltage as high as 14V. Because of the miniaturization of image sensors, automotive rear view cameras in particular have started to find their way into middle and lower segment range automobiles. An automotive camera module needs to withstand high input voltage range and deliver multiple output voltages and load currents at very high step-down ratio. The choice of DSP, sensor and micro-controller will determine overall load current of the application. Though the camera system with PMIC will be quite low power in an automobile, it is also an extremely small board in a hot environment and hence good power efficiency becomes important. Therefore, the PMIC needs to have good efficiency not only at peak load condition but also at moderate and light load condition. Recent trends on high-voltage high step-down ratio power converters are pointing towards voltage regulator modules with high power requirements (>10W). The power transistors are discrete and only the controller is integrated into the IC. However, with increasing number of moderate power applications like automotive camera modules, there is renewed interest to look into design of low-cost power converters that can deliver moderate load power (1-3W). The power management unit (PMU) designed needs to be robust to the wide supply voltage transients and withstand high ambient temperature of 105 ◦ C. Due to self-heating of the PMU, the circuits need to be designed to be robust for IC junction temperatures close to 150 ◦ C. An affordable, reliable and highly-efficient automotive reverse camera system is found to have all the required challenges for a VLSI designer to make it a very interesting research problem for this thesis work. A combination of DC-DC (switching converters) and low-dropout (LDO) regulator, which is known as hybrid regulator, is found to give the best compromise in terms of system efficiency, output voltage ripple while keeping the overall component count to the minimum. State-of-the-art hybrid regulators have high-efficiency in a very limited load range. The LDO dropout voltage which is decided by the peak load current requirement is the main source of inefficiency at moderate and light load condition. There are also several works that deal with the light-load efficiency improvement of the switching converters but they have either low supply voltage or limited load current range. This work focusses on a generic system efficiency improvement solution based on the adaptive dropout of the LDO has been proposed. Optimal circuit design architecture with adaptive LDO dropout has been implemented to handle single DC-DC and upto three LDOs with independent voltage and current requirements. AMS 0.35μm high-voltage CMOS technology with 50V transistors and isolated 3.3V transistors have been used to design the power management circuits. An optimal two-chip PMIC solution with hybrid regulators has been proposed to meet the power supply requirements of rear-view camera application. The design of the two PMICs have been successfully completed and fabricated. The packaged ICs have been tested for their functionality. The innovation has been successfully validated in the lab and the experimental results prove the improved efficiency with respect to the conventional hybrid regulator across the 95% of the load current range and IC junction temperature upto 150 ◦ C. The design has been benchmarked also with state-of-the-art commercially available PMICs. Though a specific application like automotive reverse camera has been chosen to define the thesis goals, the novel contributions of the thesis work is very generic and can be applied to any hybrid voltage regulators with DC-DC and LDO combination. Full thesis: pdf Centre for VLSI and Embeded Systems Technology |
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