Now, one power module can suit multiple applications without any changes in its design or size! Miguel A. Mendoza, marketing manager, Micrel Inc., talks to Sneha Ambastha about the beneficial aspects of modern power modules.
Q. What is the current trend of the power modules?
A. The trend in modules is to achieve smaller solutions while maintaining the same power output, as well as to eliminate any additional design work for the customer. Our customers would like to see small, turnkey solutions that do not require making any decisions on what resistors to choose or size capacitors. The fewer components required, the more attractive the solution becomes. They would also like to use two or three modules to scale the power needs of their solution when required. This will allow them to use the same module block across many platforms, maximizing the cost benefit and reducing the need to validate new components. We are currently designing the next controller to help us achieve this demand.
Q. How does the high switching frequency of modern power modules help reduce the size of the output capacitor?
A. In general, a higher switching frequency allows for a smaller inductor and output capacitor, reducing the total solution size and monetary value. In case of the power module, the inductor is fixed since it’s inside the package. A fast transient response is what allows a customer to use small and inexpensive ceramic capacitors. The modules also offer a programmable switching speed from 200 KHz to 600 KHz, to get the best efficiency in the application. For example, the MIC28304 power module from Micrel could be used in an application with a 48V input supply and a program output voltage of 5V, where switching to 275 KHz would offer the best power efficiency, since the duty cycle of the field-effect transistor (FET) would be a lot shorter. The same device could be used to run at 12V input supply and 5V output voltage. At this electrical rating, using a higher frequency of 600 KHz would offer the best power efficiency since the switching duty cycle would be a lot larger. Switching faster allows higher power efficiency and the inductor does not get saturated.
Q. Does the high density of modern power modules make them suitable for a wide range of applications?
A. Power density is an industry term, which means being able to drive a lot of current or use very high input in a very small package. Even though our module can drive max currents at 3A, 6A, 10A, or 14A, customer applications don’t require the same supply currents in all applications or solution blocks. Their application requirements can vary from 1A to 12A, and the ability to use one solution that is very small in size and can serve multiple current requirements is very valuable to them. The benefit is that the customers can use the same power block to supply power to many applications without increasing the board space or any changes to their design. It allows the customers to reuse the same power block, to utilise a proven design over and over again. They also get better volume pricing on the module as they use the same part number at high volumes versus designing a new power block for each application every time.
Q. In comparison to the high-density power modules, how do you think that the low-density power modules would sustain in the industry?
A. They will eventually fall out favour, as they will be most costly compared to the smaller devices. In the end, we are all limited by material costs, test time and assembly. Making smart decisions on the mechanical assembly, material and component choices, as well as the circuit design, is critical to get to the price target of our customers.
Q. How does the surface-mount quad-flat, no-leads (QFN) package compare with other options like Dual Flat No-Lead (DFN) Packages or micro lead-frame packages (MLP)?
A. For the initial micro-module family release, we focused on the QFN package to offer our customers an overall solution size advantage. In the QFN package, the copper lead frame offers excellent thermal performance that allows our solution to de-rate heat more efficiently, allowing the device to offer more power density compared to its competitors. We are actively looking at other packages to address all customer applications and manufacturing limitations, as we understand that QFN packages are not always preferred by all of our customers.
Q. In what way does the copper lead frame contribute to the thermal performance of the power modules?
A. Copper lead frame has lower thermal resistance compared to printed circuit board (PCB) modules or multi-ball grid array modules. It also has lower electrical resistance, which minimises power losses that can be an issue in high current applications. Hence, the copper lead frame technology enables our devices to drive more current in a very small package. For example, Micrel’s MIC45212 can drive an output current of 14A in a small 12mm x 12mm x 4mm package. We spent a lot of engineering time to design a lead frame that allows our customers to use a very simple landing pattern on the PCB for easy manufacturing and reliability, without compromising the thermal de-rating.