An Inductive Down Converter System-in-Package for Integrated Power Management in Battery-powered Applications

With the increasing number of voltage conversions that have to be efficiently implemented in a mobile device, the PCB space occupied by switched-mode DC-DC converters with external passive components will become unacceptably high. Therefore, a clear need exists for small-form-factor high-efficiency DC-DC converters having the necessary passive components integrated within one package. This will enable the integration of a DC-DC converter with the load and consequently the system integration of power management. This paper describes the measurement results of an integrated inductive down converter, where the active electronics (power stage and driver circuitry) has been implemented in 0.18-mu m CMOS technology and the passive components (output LC filter and decoupling capacitor) have been implemented in a state-of-the-art proprietary passive-integration process technology using high-density trench-MOS capacitors (80 nF/mm(2)) and an 8-mu m thick copper top metallization layer. The active die of the converter has been flip-chipped on top of the passive die to reduce parasitic component values. This yields a System-in-Package (SiP) that achieves a step-down DC-DC conversion without any external components. Due to the limited inductance achievable with the used planar air coil in the acceptable area, the switching frequency of the DC-DC converter has been increased. At the same time, Zero-Voltage-Switching (ZVS) measures have been implemented to reduce the switching losses at this increased frequency. A maximum efficiency of 65% at 80 MHz has been achieved for an input voltage of 1.8 V, an output voltage of 1.1 V and an output current of 100 mA. After explaining the motivation behind integrated power management and the choice for an integrated inductive converter, this paper describes the main design aspects of the realized integrated inductive DC-DC down converter. Next, it presents some details of the used passive-integration process, the design of the passive die including the LC filter and the construction of the SiP. Finally, the measurement results of the converter are discussed and conclusions are drawn.