Increasing Power Density with Dual-Channel Power Modules

Looking specifically at test and measurement or optical module applications, the problem statement is no longer limited to the area (x-axis and y-axis) of the design; rather, it becomes a three-dimensional jigsaw puzzle, where the height (z-axis) of a design is also a constraint.

Fortunately, you can use high-power-density buck power modules to add much-needed flexibility to your power design. A buck power module integrates a buck controller, power switches, a powerstage inductor, and other passives such as high-frequency bypass capacitors and compensation components, all in a single device. In this article, I will explain how modern power modules, in particular dual-channel modules, help address challenges related to solution footprint area and z-height through multiphase operation.

 

Shrink Your Solution Size

In industrial applications such as test and measurement and avionics, designers must meet stringent solution-size constraints in all three dimensions. Modern high-power-density modules help meet these requirements by offering tighter integration, unique board placement and closer placement to loads. They further save board space and reduce bill-of-materials cost by integrating passives such as high-frequency capacitors, bootstrap components, and one or more power-stage inductors. Using a bare die within the integrated circuit makes it possible to place high-frequency capacitors closer to the power stage within the module than when using a discrete converter, especially if there are printed circuit board (PCB) component clearance constraints. These solution-size benefits apply to both single- and dual-channel power modules.

 

Get More Flexibility on the Board

In applications with height constraints, low-profile power solutions can open up new possibilities in the PCB layout. The system’s physical form factor, or system enclosure, can limit the component height on the back side of a PCB, thus reserving that part of the board for low-profile components such as capacitors and resistors. You could tuck a low-profile module underneath the overhang of a heat sink of another device, like the heat sink of a field-programmable gate array or processor itself, making use of previously restricted board area. As shown in Figure 1, the TPSM5D1806 buck power module is one example of a low-profile module. At 1.8-mm tall, the TPSM5D1806 is shorter than many 1206 or 1210 ceramic capacitors.

 

Figure 1: Low-profile design of the TPSM5D1806 power module with surrounding bypass capacitors. Image used courtesy of Bodo's Power Systems.

 

The low z-height, combined with the small x-y solution size, may open up options to place the power module closer to the loads it is powering, which enables more accurate and effective regulation by reducing longer parasitic traces. You will still need to place taller solutions farther away from the load.

 

Take Advantage of Dual-phase Operation

While both single- and dual-channel modules offer the benefits of smaller solution size and the increased flexibility of placing components on the board, dual-channel power modules such as the TPSM5D1806 have a unique advantage over single-channel power modules when it comes to power density. In addition to dual-output mode (see Figure 2), designers can use a dual-channel power module and connect them together into a single-output, dual-phase configuration. Splitting up the current between the two integrated inductors enables you to use vertically shorter inductors, each with lower saturation current ratings, saving space in the z-axis. In contrast, a single-phase solution would require a taller inductor to match the current capability of a dual-phase solution.

 

Figure 2: TPSM5D1806 power-module design layout in a dual-output configuration. Image used courtesy of Bodo's Power Systems.

 

Dual-output modules also require less input capacitance by switching the channels out of phase from each other, reducing the peak and root-mean-square input currents and further saving space in the x- and y-axis.

 

Conclusion

Implementing dual-channel buck power modules into a design can help you take advantage of all of the power-density benefits associated with power modules, including a small solution size with a low profile, more board space and greater flexibility for other design considerations. However, dual-channel power modules offer additional power-density advantages when used in a single-output, dual-phase configuration, helping you work more easily in tight and power-dense designs while maintaining the flexibility of choosing between single-output (dual-phase) or dual-output (one phase per output) configurations.

 

This article originally appeared in Bodo’s Power Systems magazine.