The input voltage and output current capabilities of synchronous, step-down dc-to-dc converters with integrated MOSFETs have been steadily increasing. Many reputable vendors offer devices that support dc-to-dc conversion from a 12-V input with output currents above 10 A. Until recently, a dc-to-dc controller with external FETs was the only solution for these applications. Today, higher current and input voltage dc-to-dc converters with integrated MOSFETs are mainstream due to packaging and process improvements.
Multi-chip dc-to-dc converters typically integrate an off-the-shelf controller and power MOSFETs using two discrete MOSFETs or a single-chip MOSFET pair attached to a custom lead frame. Wire bonds connect the controller and MOSFETs to the lead frame and the controller to the gates of both MOSFETs. The assembly is encapsulated with epoxy and parametrically tested. Monolithic dc-to-dc converters integrate the controller and MOSFETs on one piece of silicon. The single die is attached to a lead frame, wire bonds connect the die to the lead frame, and the assembly is encapsulated and tested.
Over the last four years, monolithic dc-to-dc converter package sizes manufactured in a Bi-CMOS process have been reduced by as much as 80%, while switching frequencies have been increased by 2X to 3X. While many monolithic devices are on the market that support a 3.3- or 5-V input, only recently have 12-V devices become prevalent. Figure 1 shows a monolithic 4.5- to 17-V input dc-to-dc converter in a 3.5- by 3.5-mm QFN package. The device is rated by the manufacturer for 6-A continuous output current and can dissipate 2.27 W at 25°C. Figure 2 shows a 3- to 14-V input multi-chip converter rated by the manufacturer at 10 A in a 5- by 7-mm package that dissipates 2.85 W at 25°C.
Monolithic dc-to-dc converter in a 3.5- by 3.5-mm package.