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 Vin-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 Vin-referenced feedback voltage of Vfb = Vin − Vn, the proposed translator generates a ground-referenced voltage of Vn with a variation of only 0.6 mV over a wide range of Vin 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 µVrms 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.