Use Point-of-Load Switching Converters to Optimize Your Power Distribution Architecture

The architecture of the power distribution network that supplies a printed circuit board (pc board) or system has evolved dramatically over the past decades. This shift reflects changing system priorities and the broader range of voltages and currents required by various loads. At the same time, nominal rail voltages have decreased, such as 0.8 volts for an ASIC, 1.2 volts for a processor core, 1.8 volts for system I/O, and 3.3 volts for other circuit functions, along with tighter voltage-rail tolerances and increased power demands.

Overall, these changes have increased the emphasis on supply efficiency, thermal loading, noise, transient response, and other factors related to the power distribution network (PDN) and its branches. To meet these changing requirements, we need to consider the appropriate architecture before selecting the right power delivery solution.

PDN architecture options

Three widely used PDN architectures can provide multiple low-level rail voltages (most under 10 volts) to individual loads: centralized, decentralized, and intermediate. Let’s quickly look at each:

Centralized: In the classic centralized architecture, a main AC/DC supply feeds an array of DC/DC converters, each producing a rail voltage distributed to one or more loads. All loads at the same nominal voltage, regardless of their location or individual current needs, are powered by a single DC/DC converter. These DC/DC converters are often located far from their dispersed loads, creating several challenges.

First, power-rail runs induce IR voltage drop and associated I²R power dissipation. While remote sensing can compensate for the voltage drop at one load, it does not eliminate conductor loss. Extending the feedback path to the load also introduces wiring impedance and noise susceptibility that must be considered when assessing loop stability. In addition, one remote-sense point cannot correct the different voltage drops experienced by multiple dispersed loads.

The inductance of the pc board traces, or wire leads between the DC/DC converter and the load, affects the converter’s response to load transients, creating another challenge. These supply-rail traces or leads are susceptible to noise pickup, which the load then sees.

Decentralized: In contrast to the centralized architecture, the decentralized (distributed) approach places multiple point-of-load (PoL) converters very close to their respective loads (Figure 1). A larger DC/DC converter downstream of the AC/DC supply provides the input DC voltage, typically 12 or 48 volts, to the array of PoL converters, which then supply the required load voltages.

Figure 1: A decentralized architecture places each PoL converter close to its respective load. (Image source: TRACO Power)

Unlike the centralized arrangement, where a single voltage source supplies multiple components at the same nominal voltage, this solution gives each localized load its own converter to provide the needed voltage and current without excess. Even loads with the same nominal voltage but in separate locations get their own PoL converter.

By placing the PoL converter next to its load, you greatly reduce issues associated with the conductive path between the DC/DC PoL converter and its load. Instead, the load receives a locally regulated rail matched to its voltage and current requirements.

Intermediate: Of course, not all architectural choices are a binary “either/or” decision. The intermediate architecture (Figure 2) balances elements of centralized and decentralized approaches. Some wide-input-range PoL converters connect directly to the main DC bus, while others receive power from a central DC/DC converter that produces a lower intermediate voltage, such as 12 volts. This voltage is then routed via a distribution network to local PoL converters, which generate the final voltage for the loads.

Figure 2: The intermediate approach combines PoL converters connected directly to the main DC bus with others supplied through a central DC/DC converter. (Image source: TRACO Power)

This step-by-step voltage conversion simplifies the design by distributing extreme voltage conversions across several more manageable stages and a wider choice of PoL converters. At the same time, it enables faster, more stable regulation near the load and provides a flexible, scalable supply for multiple loads. It is a compromise that offers many benefits of the decentralized approach while enabling some PDN flexibility.

PoL converter variety is a critical factor

To get the most from intermediate or decentralized architectures, you need a broad family of PoL DC/DC converters that offers a range of input and output voltages and current ratings. This way, the PoL converter can be closely matched to the specific load it supports, rather than oversized to deliver excess, unneeded current (which increases size and cost). PoL converters are commonly nonisolated because the converter and load share a system ground, while any required safety or functional isolation is generally provided upstream.

The PoL converter can be either a switching regulator or a linear low-dropout (LDO) regulator. Switching regulators are usually preferred because they convert power efficiently and generate less heat, thereby addressing two concerns. The first is supplying enough DC current to the regulator input so it can deliver enough output current, despite conversion losses. The second is heat, which stresses components and may require exotic thermal management strategies.

In contrast, less-efficient linear regulators are generally used in applications where low output noise and design simplicity are the critical priorities.

Two switching PoL converters from TRACO Power’s line of solutions, the TSR 1-2433E (Figure 3, left) and the TSR 1-4850WI (Figure 3, right), illustrate the range of available units. The range lets you match a converter to specific load requirements for input voltage, output voltage, and output current.

Figure 3: A variety of PoL converters, such as the TSR 1-2433E (left) and the TSR 1-4850WI (right), lets you more closely match the converter to the load requirements. (Image source: TRACO Power)

The TSR 1-2433E has a footprint of 7.5 × 11.6 millimeters (mm) and is 10.2 mm high. It accepts an input between 6 and 36 volts and provides a single 3.3 volt output at 1 ampere (A). It features 88% efficiency and supports full-load operation up to 60°C ambient without a heatsink or forced cooling, and operates across a temperature range of -40 to 85°C.

The TSR 1-4850WI features an ultrawide 8:1 input voltage range of 9 to 72 volts and delivers 5 volts at 1 A. It has an efficiency of 87% and an operating temperature range of -40 to 80°C (up to 50°C without derating) in a 12.1 × 8.6 × 17.5 mm package.

Conclusion

You can choose among centralized, decentralized, or intermediate power-distribution network architectures to meet changing design requirements. By offering a wide range of PoL DC/DC switching converters, TRACO Power lets you choose a converter optimally sized for each PDN load.