Design Options for Thermal Shutdown Circuitry with Hysteresis Width Independent on the Activation Temperature

Abstract

This paper presents several design options for implementing a thermal shutdown circuit with hysteretic characteristic, which has two special features: a programmable activation temperature (the upper trip point of the characteristic) and a hysteresis width largely insensitive to the actual value of the activation temperature and to variations of the supply voltage. A fairly straightforward architecture is employed, with the hysteresis implemented by a current source enabled by the output of the circuit. Four possible designs are considered for this current source: VBE/R, modified-VBE/R, Widlar and a peaking current source tailored for this circuit. First, a detailed analytical analysis of the circuit implemented with these current sources is performed; it indicates the one best suited for this application and provides key sizing equations. Next, the chosen current source is employed to design the thermal shutdown protection of an integrated Low-Dropout Voltage Regulator (LDO) for automotive applications. Simulation results and measurements performed on the silicon implementation fully validate the design. Moreover, they compare favorably with the performance of similar circuits reported recently.

Keywords

• bipolar integrated circuits
• hysteresis
• integrated circuit reliability
• power system protection
• thermal analysis