Thermal simulation aided 98mJ integrated high side and low side drivers design for safety SOCs

Abstract

Power Semiconductor devices used for high voltage, high current applications dissipate lot of power thereby rapidly increasing their junction temperature to levels beyond which no SPICE (Simulation Program with Integrated Circuit Emphasis) models exist. In this paper, the design of an integrated four channel squib driver SOC (System on Chip) with four High Side (HS) drivers and four Low Side (LS) drivers is presented. 98mJ energy limited current regulating High Side (HS) driver needs the temperature information from the electro-thermal simulators like FloTHERM during the design to ensure that the powerFET operates within the thermal SOA (Safe Operating Area) without area penalty. Despite SPICE model restrictions to 200°C, this paper explains how the current regulation loop architecture is chosen to operate at peak temperatures of 400°C. The Thermal simulation results aid in the optimization of the layout of the gate-driver. Apart from the robust design, additional design measures to prevent inadvertent turn ON of the FETs and reverse protection for safety are discussed. This circuit was successfully implemented in a 40V, 0.35pm, BiCMOS process on a 4 channel airbag squib driver IC.