Power Tips: Hooray for integrated FETs!

PCB layout is one of the most important jobs for a power supply designer.  Every engineer that worked on power supplies has made a mistake on the PCB that caused the power supply to not work properly.  In addition, when you let people that don’t know anything about power supplies try to do a board layout it is a recipe for disaster!

Things are not as bad as they may seem, advances in packaging and IC technology have created a new class of products that may help with these issues.  Power supply control ICs with integrated power switches (FETs) are quickly taking over the point of load market.  DC to DC point of load converters are typically used to generate low voltage rails (1V to 5V) from an intermediate bus (5V to 12V).  Less than 10 years ago, it was difficult to find parts with integrated FETs that could supply more than 3A of output current.  Now it is becoming common to find low voltage input (3V to 6V) and mid voltage input (up to 30V) parts with a current handling capability of up to 30A.

Integrated FET circuits offer a number of advantages over conventional controllers plus external power switches:

  1. Smaller size
  2. Driver and dead time can be optimized for the internal FETs
  3. Higher frequency operation
  4. More efficient

Due to advances in packaging, integrated FET ICs are becoming smaller and more efficient.  The packaging allows for better heat transfer to the PCB.  The FETs themselves are also improving in size and on resistance.  An integrated FET IC can be optimized by properly sizing the driver and controlling the dead time between switching.  These optimizations allow the IC to run at higher frequencies and operate in a more efficient manner than controllers with external FETs.

Here is one example of a new design on Powerlab using the latest integrated FET ICs (with more to come!):

PMP9146 – 12V input to 1V at 12A output using the TPS53515.  This design runs at 600KHz and uses all ceramic output caps to keep the size small.  The DCAP3 control scheme allows for very fast transients with no compensation.  The load regulation is kept almost constant due to the control strategy.  Efficiency is over 85% for almost the entire load range.

I will update when new designs show up on the web and please share in the comment section below if you have any designs of your own using integrated FET ICs!