I’ll never forget the first time I saw a power supply overheat and burst into flames.
It was the spring of 2003 and our senior project was on fire (literally) because one of the members of my group tried to run 25W of current through a linear regulator that was probably better suited for about 5W, with no airflow and no heat sinking. Rookie mistake. Happens to everyone, right?
Aside from my partner’s bonehead miscalculation in college, thermal design for a switching power supply can actually be quite challenging if you aren’t using the right part. Factors like pin configuration, placement of vias, copper area and thickness, and exposed thermal pads all play a big part in keeping your supply as cool as possible and preventing failures (and fire).
The new synchronous SIMPLE SWITCHER family with input voltage up to 60V, and output current to 3A
With the new family of SIMPLE SWITCHER® LM4360x and LM4600x synchronous converters (see table above), it’s easier than ever to take the black magic out of creating a good thermal design. It starts with the package.
The entire family comes in a pin- and footprint-compatible HTSSOP-16 package. The “H” means that there is an exposed thermal die attach pad (DAP) that helps dissipate heat out of the package as efficiently as possible. As opposed to other devices that might have multiple DAPs, this family features one large DAP that is connected to ground, which makes it easier to connect to the PCB ground plane as well as effectively cluster vias together to dissipate heat to other layers.
Figure 1: Optimal heat spreading is possible with an unbroken copper ground plane in the “dogbone” shape, connected to the DAP
Having pins on two sides of the package instead of four also works to our advantage. This means the copper ground plane does not need to be broken by the routing of signals, and can be formed into a dogbone shape that allows optimal spreading of heat away from the device (see Figure 1).
Figure 2: LM43603, 12Vin to 5Vout, 3A output, 500kHz, 24.3°C ambient temperature
The cherry on top is that this excellent thermal performance can all be simulated for free using TI’s WEBENCH® online design tool. You can start a WEBENCH design using your Vin, Vout, Iout, TA input parameters, and click the “thermal” tab (looks like a thermometer) once you have chosen a device to design with. From there you can enter parameters for ambient temperature and copper weight, while simulating air flow to get strong indications of how the device will perform in your design (see Figure 2).
Taking this even one step further, you can also download the layout from your WEBENCH design and copy and paste it right into your CAD tool. Watch this video for a detailed look at how to do it. So if you’re looking for an easy way to design your system with good thermal performance and reliability, look no further than the new SIMPLE SWITCHER LM4360x and LM4600x synchronous converter family. For more details, check out the thermal Design Made Simple App Note and video.
