LINEAR AN119B-1 Data Handbook/Manual

Application Note 119B

April 2008

Powering Complex FPGA-Based Systems Using Highly Integrated DC/DC µModule Regulator Systems Part 2 of 2 Thermal Performance and Layout Alan Chern and Afshin Odabaee

60W by Paralleling Four DC/DC μModule Regulators Thermal Performance In part one of this article, we discussed the circuit and Figure 2 is a thermal image of the board shown in Figure 1 electrical performance of a compact and low profi le 48A, with readings of the temperatures at specifi c locations. 1.5V DC/DC regulator solution for a four-FPGA design. The Cursors 1 to 4 show an estimation of the surface tem- new approach uses four DC/DC μModule® regulators in perature on each module. Cursors 5 to 7 indicate the parallel (Figure 1) to increase output current while shar- surface temperature of the PCB. Notice the difference in ing the current equally among each device. This solution temperature between the inner two regulators, cursors 1 relies on the accurate current sharing of these μModule and 2, and the outside, cursors 3 and 4. The LTM4601 regulators to prevent hot-spots by dissipating the heat μModule regulators placed on the outside have large planes evenly over a compact surface area. Each DC/DC μModule to the left and right promoting heat sinking to cool the regulator is a complete power supply with on-board inductor, part down a few degrees. The inner two only have small DC/DC controller, MOSFETs, compensation circuitry and top and bottom planes to draw heat away, thus becoming input/output bypass capacitors. It occupies only 15mm × slightly warmer than the outside two. 15mm of board area and has a low profi le (height) of only

Airfl ow also has a substantial effect on the thermal balance

2.8mm. This low profi le allows air to fl ow smoothly over

of the system. Note the difference in temperature between

the entire circuit. Moreover, this solution casts no thermal

Figures 2 and 3. In Figure 3, a 200LFM airfl ow travels

shadow on its surrounding components, further assisting

evenly from the bottom to the top of the demo board,

in optimizing thermal performance of the entire system.

causing a 20°C drop across the board compared to the no airfl ow case in Figure 2. L, LT, LTC, LTM, μModule, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Figure 1. Four DC/DC μModule Regulator Systems Current Share to Regulate 1.5V at 48A With Only 2.8mm Profi le and 15mm × 15mm of Board Area for Each Device. Each μModule Regulator Weighs Only 1.7g and Has an IC Form-Factor that Can Easily be Used With Any Pick-and-Place Machine During Board Assembly

an119bfb

AN119B-1