Low temperature evaluation of bipolar- and CMOS-based current-mode PWM controllers

Two commercial-off-the-shelf (COTS) current-mode controller integrated circuits (ICs), with potential use in the development of a low temperature DC/DC converter, were evaluated at cryogenic temperatures. The design of the two ICs is identical but one is bipolar-based and the other is CMOS-based. Both ICs are capable of high frequency switching (200-500 kHz) and are specified for operation in the temperature range of 0 °C to +70 °C. Two separate circuit boards utilizing these controllers were built and evaluated in the temperature range of +20 °C to -185 °C. The performance of each controller in terms of its switching frequency and duty cycle control was evaluated as a function of temperature. Under short-time exposure to low temperature, the bipolar-based IC displayed good operational behavior with temperature only down to -110 °C. Beyond that temperature, the device lost its functionality but recovered when higher temperatures were introduced. Nonetheless, the low temperature limit of -110 °C by far exceeds the manufacturer´s temperature specification of the device. The CMOS-based current-mode controller, on the other hand, displayed good operational behavior down to -185 °C. While slight changes were observed in some of the device parameters upon exposure to low temperature; no significant impact, however, resulted on its overall performance.