A feedback-voltage-sensing translator for floating buck DC-DC converters

A feedback-voltage-sensing translator for floating buck DC-DC converter is designed for CSMC´s 0.5 μm 60 V BCD process. The proposed circuit utilizes one NPN, one PNP and a resistor to translate a V_in-referenced (input voltage as the reference, instead of GND) feedback voltage to a current, which is then translated to a ground-referenced voltage with another two bipolar transistors and one resistor. High precision translation is accomplished based on the equivalent base-emitter voltages of the bipolar transistors. Simulation results show that, for a V_in-referenced feedback voltage of V_fb = V_in - V_n, the proposed translator generates a ground-referenced voltage of V_n with a variation of only 0.6 mV over a wide range of V_in from 18 to 60 V. The translator also achieves a low temperature coefficient of 6.9 ppm/°C from -40 to 125 °C. Additionally, the noise of this translator is only 3.46 μV_rms from 0.1 to 10 Hz and the PSR is -98 dB @ DC. The translator is verified via Spectre simulation in a floating buck converter.