Analogue DC/DC controller minimises PCB space for inductors

October 23, 2013 // By Graham Prophet
Using dynamic temperature-compensated inductor current sensing, this 20-V DC/DC synchronous buck controller delivers greater than 95% efficiency with smallest inductor footprint

Texas Instruments has introduced an analogue DC/DC step-down controller with remote bipolar junction transistor (BJT) temperature-compensated inductor current sensing that minimises total PCB footprint in high-power POL conversion applications. The 20-V LM27403 DC/DC synchronous buck controller provides greater than 95% efficiency from a 12-V input at 25A output current to deliver fast transient response in communications infrastructure, industrial, medical and power module applications. Used in conjunction with TI's WEBENCH online design tool, the LM27403 simplifies DC/DC conversion and speeds the design process.

The temperature-compensated inductor DC resistance sensing uses a low-cost BJT to measure real-time temperature shifts, allowing the LM27403 to maintain a consistent current-limit threshold, within 10%, across the operating temperature range. The current limit accuracy over temperature results in a smaller DC/DC converter footprint that reduces inductor over-design and allows for the use of smaller and lower-cost inductors. A video demonstration of temperature-compensated inductor current sensing here.

The LM27403 provides a complete dynamic voltage solution when designed together with TI's LM10011 voltage identification (VID) interface controller and 30-V CSD87350Q5D synchronous buck NexFET Power Block MOSFET to adjust the core voltage (VCORE) of a VID-enabled processor. Features include;

- 3-V to 20-V input voltage range converts 3.3-V, 5-V and 12-V input voltage rails to point-of-load (POL) as low as 0.6V with 1% accuracy.

- 30-nsec minimum on-time allows higher switching frequencies at lower duty cycles, providing greater scalability and smaller solution size.

- 15-nsec adaptive dead-time control provides higher efficiency in high frequency operation, reducing power consumption.

- Output voltage remote sensing gives improved load regulation in high current applications.

The LM27403 comes in a 4 x 4 x 0.8-mm, 24-pin PowerPad WQFN package, for $1.20 (1,000) Downloadable reference designs cover examples for 1.8V/30A synchronous buck converter (4.5V to 20V input); 0.9V/30A synchronous buck converter (12V input); and 0.9V/45A single phase synchronous buck converter (12V input).


A video on how to design a high performance converter