Multiphase synchronous rectification has seen extensive application in high-current, low-voltage step-down applications. With the LTC3425 synchronous boost converter, Linear Technology extends the benefits of multiphase design to lower-power step-up applications. A four-phase converter with an effective switching frequency of 8 MHz, the LTC3425 integrates four n-channel MOSFET switches and four p-channel synchronous rectifiers, which produce a continuous output current of 3 A.
The chip converts an input in the 0.5- to 4.5-V range to an adjustable output at 2.4 to 5.25 V. The four-phase approach allows the boost converter to operate with four low-value inductors. The reference design shows a value of 2.2 µH for each of the inductors. They may be shielded or toroidal types, measuring just 1.5 mm tall. Another distinguishing feature is the chip's true output disconnect, which eliminates inrush current and allows zero load current in shutdown. It comes in a 32-pin QFN and costs $4.38 each in 1000-unit lots.