Automotive Switched-Capacitor DC-DC Converter with High BW Power Mirror and Dual Supply Driver

Abstract

This paper presents circuit topologies and implementations for SC DC-DC converters with controlled charging current. It focuses on the power current mirror that regulates the charging current of the flying capacitor and on the switch drivers. The bandwidth and transient response of the power mirror are improved by inserting an auxiliary current mirror in its input signal path. Conventional switch drivers need power supplies with fast response to load transients; the driver presented here is less demanding, as only its core is biased internally, while the output stage is supplied directly by the converter input voltage. The circuit has an additional 'Linear Regulator' mode of operation, whereby the power mirror is turned into a pass transistor. This expands the low-end limit of the converter input voltage. These solutions were used to design in a 130nm BCD technology an automotive SC DC-DC converter. Simulations and measurements performed over the entire automotive temperature range (-40C to +150C), for supply voltages between 8V and 28V, demonstrate that the converter meets all requirements: it can operate with output capacitors as small as $1\mu \text{F}$ ; it provides regulated 5V output voltage for load currents up to 200mA, ensuring a low output voltage ripple, of 35mV and 9mV for output capacitors of $1\mu \text{F}$ and $10\mu \text{F}$ , respectively; its efficiency peaks at 81.3% for the typical battery voltage level, 12V.