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|System ElectroThermal Co-Design of a Zero-Drift Current-Shunt Monitor with Precision Integrated Shunt Resistor|
|Keywords: System Co-Design, ElectroThermal, Silicon Measurement to Modeling Correlation|
|The goal: A coupled electrothermal co-analysis methodology is proposed. The methodology contains two functional modules: 1) physical field solvers and 2) equivalent circuit/network solver. The field solver resolves the electrical and thermal field variables by the conventional 3D finite-element method, while the network solver can achieve accurate and efficient results by connecting the equivalent electrical, thermal and flow circuits that are extracted from the system through advanced numerical computational schemes. The integrated equivalent network can then be solved by a generic circuit solver for steady state and transient responses. The methodology is demonstrated, via simulation and measurement, on a Zero- Drift Current-Shunt Monitor with Precision Integrated Shunt Resistor - the INA250tm. Good correlation between modeling methodology and laboratory measurements is achieved. The Methodology/Concept: Coupled ElectroThermal Solvers Current is a function of device temperature, which in turn, is determined by the dissipated power. Therefore the determination of device current (i.e. power) and a temperature represents a coupled electro-thermal problem. The co-analysis methodology contains two functional modules: 1) physical field solvers and 2) equivalent circuit/network solver [1- 2]. The field solvers resolves the electrical and thermal field variables by the conventional 3D finite-element method, while the network solver can achieve accurate and efficient results by connecting the equivalent electrical, thermal and flow circuits that are extracted from the system through advanced numerical schemes including Finite-Element Analysis (FEA) and Computational Fluid Dynamics (CFD). The integrated equivalent network can then be solved by a generic circuit solver for the transient and steady-state responses due to electrical and thermal interaction, and the heat dissipation to the surrounding fluid is also taken into account. In the physical conventional field solvers the governing equations are solved iteratively based on the physics of electrical and thermal formulations respectively. The electrical conductivity tensor is a function of temperature. For electrical  and thermal  solutions, Ohm's Law and the Thermal transport equations are solved respectively. To effectively carry out electrothermal co-simulation, the boundary conditions to be imposed to the problem are critical to achieve results that are coherent with physics and fit for realistic applications. Electrical boundary conditions should include the driving forces of electrical potential and the current requirements on the package and die to perform the functions as designed. These electrical boundary conditions are applied at specific ports or terminals in the geometrical model. Thermal boundary conditions are basically characterized as heat-in and heat-out mechanisms associated with the system. In general, the heat-in mechanism is the power input (or consumption) through the chip, and the heat-out mechanisms account for heat dissipation out of the system, including conduction, convection, and radiation . Once the electrothermal analysis is done, a thermal network model is derived based on reduced state-space approximations. System Description and Results: The ElectroThermal methodology discussed above was implemted on TI INA250tm. The INA250 is a voltage- output, current-sensing amplifier family that integrates an internal shunt resistor to enable high-accuracy current measurements at common-mode voltages that can vary from 0 V to 36 V, independent of the supply voltage. It is a bidirectional, low- or high- side current-shunt monitor that allows an external reference to be used to measure current flowing in both directions through the internal current-sensing resistor sensor. The integration of the precision current- sensing resistor provides calibration equivalent measurement accuracy with ultra-low temperature drift performance and ensures an optimized Kelvin layout for the sensing resistor is always obtained. DC resistance and thermal (Joule Ohmic heating) measurements were peformed to correlate with modeling. Good correlation observed between laboratory silicon measurements and simulation for DC resistance and Joule/Ohmic heating: DC resistance: DC Multimeter (Kelvin probe): Measurements: 1.998mΩ Simulation: 2.054mΩ Joule Heating:Infrared Imaging (IR): Measurements: [98.8–103.9]oC Simulation: [99.4–106.2]oC|
|Jie Chen, Electrical Modeling Engineer
Texas Instruments, Inc