5 MHz switching micro DC-DC converter using planar inductor

The authors describe a high frequency switching DC-DC converter using a novel developed planar inductor. The planar inductor has a sandwich structure, which consists of a 50 /spl mu/m thick copper rectangular spiral coil between upper and lower 6 /spl mu/m thick FeCoBC amorphous magnetic films. The typical specifications of the inductor are as follows: 5.50/spl times/6.55 mm/sup 2/ in size, inductance of 0.30 /spl mu/H constant up to 10 MHz, DC resistance of 0.16 Ohms, a maximum quality factor of 8 at 2 MHz, and a maximum DC current of 1.6 A at -6 dB inductance point. A 5 MHz switching step up converter has been developed, which has the planar inductor, Nch lateral MOSFETs for main switch, a low Vf Schottky barrier diode, multilayered ceramic capacitors and a MHz operation PWM control IC. These components have been surface-mounted on circuit board, and then molded by epoxy resin. The novel developed DC-DC converter has 1.3/spl times/1.4/spl times/0.2 cm/sup 3/ in size, 2 W of rating output power and 80% of typical efficiency, when an input voltage is 3.6 V and an output voltage is 4.7 V.