A Fast-Response Charge-Pump Gate Driver Applied to Linear Regulation

It ́s common practice in designing switchedcapacitor converters (SCC ́s) to keep charge-pump (CP) switches continuously commuting at light loads [1-2]. However, the resulting simplification in the control circuitry is frequently objected, as the switching dissipation prevails over the average power delivered to the load. Since the converter efficiency is degraded, such an approach does not comply with rigorous power consumption requirements for modern battery-operated applications. While saving switching dissipation, skipmode regulation [3] is a simple way to produce a wellcontrolled voltage VOUT at the converter output. In this technique, a finite wait time ∆tW is inserted between non-overlapping pulses of width ∆t. During time intervals ∆t, the energy is sequentially transferred from the power line to the flying capacitor, and from the later to the load. However, as compared to a linear-mode regulation, where ∆tW = 0, VOUT is subject to a higher voltage peaking that is increased by a factor (1+ ∆tW/∆t). Unless special care is observed, this overvoltage may stress the gate-oxide of transistors being supplied by such a rail voltage, having their life expectance abbreviated. On the other hand, linear regulation has been the preferred option to improve CP efficiency. The gate-source voltage VGS_SW applied to power switches is regulated by linear feedback control of VOUT [46,8]. An interesting variation, named linskip regulation, is proposed in [5,8] and combines both skip and linear modes. In this case, two current sources are alternately commuted by a comparator that arbitrates between the ripple on CP output voltage and a reference. An average voltage VAVG, proportional to the commuting time of these current sources, is obtained through an averaging capacitor and used as VGS_SW to drive the switches gate. Nonetheless, owing to its dependence on the settling time of VAVG, this approach does not immediately respond to load transients. To overcome such a limitation, this work introduces a compact charge-pump gate driver (CPGD) that instantaneously compares the SCC output voltage VOUT with an internal reference VREF and optimally sets VGS_SW. The circuit simple topology leads to a fast reaction to transients. The CPGD circuit is embedded in a complete SCC system that performs a linear regulation on VOUT. ABSTRACT1