Design of an Over- Temperature Protection Circuit for RS-485 Transceiver

This paper introduces an over- temperature protection circuit integrated on an RS485 transceiver chip. Since the chip does not integrate a reference voltage, a design of an over- temperature protection circuit that does not require a reference voltage is adopted. The voltage difference between the base- emitter junctions of transistors with different areas is amplified and then compared with the base- emitter junction voltage of a transistor to generate an over-temperature protection control signal. A self- biasing structure is used to optimize the voltage stability of the generated PTAT current, and a hysteresis comparator is utilized to effectively avoid thermal oscillation. Based on the Dongbu 0.18um BCD process, the circuit is simulated and verified through the Cadence Spectre tool. The simulation results show that the over-temperature protection point is between 158°C and 166°C, and the over-temperature recovery point is between 147°C and 156°C, which is basically consistent with the design values.