Digital power solution, base station power design

Base station power engineers encounter many design challenges. Wireless operators want them to reduce power consumption and size. They are also challenged to minimize subsystem complexity for sequencing, monitoring, margining, and numerous other tasks. To optimize the application requirements, they must make several trade-offs, including power conversion efficiency vs. size and performance vs. complexity vs. cost. This article will explain how a new, highly integrated power solution simplifies these design challenges by providing the flexibility and optimized performance.

Improve efficiency

The energy cost of operating a base station is of great significance to wireless operators, which makes the need for more efficient power solutions important to reduce operating costs. In addition, the lower power consumption, therefore, allows operators to use a smaller heat sink in the radio equipment. A smaller heat sink, in turn, may allow a smaller unit to be implemented. Finally, because these radio units are often mounted on a pole or the side of a building, reducing the overall footprint minimizes the mechanical stress involved.

A base station's baseband unit provides fast signal processing capabilities to handle large amounts of data and voice network traffic. Baseband units require high current and multiple voltage rails with currents that can exceed 60A, resulting in multi-phase power solutions and often the need for telemetry.

Techniques to improve power conversion efficiency by reducing heat conduction, switching, and reverse recovery losses. Selecting low (RDSON) MOSFETs can reduce conduction losses. Higher gate drive can further reduce RDSON. The tradeoff with using higher switching voltages is increased switching losses. Nonetheless, having the ability to set the gate drive can be highly desirable. For higher currents, higher gate drive voltages reduce conduction losses; for light load operation, the gate drive voltage can be reduced. An automated selection process optimizes the tradeoff between conduction and switching losses, giving base station designers a better decision.

The MAX15301 digital point-of-load (POL) controller uses advanced algorithms to achieve the highest levels of efficiency and transient response over a full range of operating conditions. It includes an advanced, high-efficiency external, adaptive gate driver for the MOSFET. It optimizes efficiency by constantly adapting to changes in load, voltage, and current.

Simplify power supply complexity and improve system reliability

If you can monitor the operating parameters of the system, then you can better manage the performance of the system. And better system management improves the reliability of the system.

As mentioned above, the baseband unit must have powerful signal processing capabilities to handle large amounts of data and voice traffic. Multiple high and low current voltages must be sequenced correctly during power-up/down. Current and temperature must be monitored throughout the baseband operation to ensure that the system is operating within tolerance and provide warning or fault signals. Finally, it is the telemetry and advance fault management functions that enable the base station to achieve high reliability. Using an analog approach, multiple devices are required to implement these functions requiring a power management. However, a digital approach reduces design complexity and requires a separate power management. (See Figure 1).

The task of base station power management typically requires a very complex power management controller and multiple discrete components for each function. The overall board space and design complexity grow accordingly. Base station designs operate at extreme temperatures, so the design must be robust over a wide operating temperature range. With traditional analog power solutions, compensation is set in a unique operating condition and must address a wide operating range. At the same time, variations in passive components such as inductors and capacitors make power compensation more challenging.

There is an alternative approach, a system based on a digital architecture approach. In a digital architecture, automatic compensation capabilities can be implemented and optimized to be advantageous bandwidth. Higher bandwidth improves load transient response, thus enabling improved tolerances or the ability to eliminate output capacitors, increasing solution size. Additionally, passive components can vary with temperature, but the automatic compensation function can adapt to these changing conditions. This provides the ability to optimize over the entire temperature range.

Figure 1. System design with analog (left) and digital approaches (right). The digital approach integrates power management for each DC-DC converter. The result is a flexible and scalable system. Digital telemetry system components enable continuous monitoring to ensure base station performance is optimized.

Maxim InTune™ products such as the MAX15301 address these power management challenges. They make it easy to implement high-performance DC-DC power supply designs that require fewer filter capacitors and have higher efficiency. This digital power technology is based on "state-space" or "model predictive control" rather than proportional-integral-derivative (PID) control, which is typical of most digital controllers. The automatic compensation routine in the MAX15301 is based on the measured parameters, enabling the construction of a mathematical model of the internal power supply including external components. The result is a switching power supply that achieves the highest possible power performance while ensuring stability. This technology also enables a number of proprietary algorithms to optimize efficiency over a wide range of operating conditions.

Reduce board space

Reducing board space in radio equipment is important because antennas can be mounted to buildings, towers, or poles, where weight becomes an issue. For baseband units, larger, more powerful digital processors require more space, therefore, making it more challenging to keep board size down.

An integrated MOSFET solution offers a smaller form factor for POL power supplies. This approach is acceptable at lower power levels, but it becomes more challenging with higher current designs. Integrated MOSFET devices are optimized for efficiency under specific operating conditions. A controller-based solution allows some flexibility for optimization because you can optimize the MOSFET selection for each specific condition. It also allows for more heat spreading across the board for thermal management. The obvious tradeoff here is the need for more board space.

At the same time, the currents in the baseband unit can be as high as 60A per rail, requiring a multiphase power solution. These higher power rails, in this case, increase the number of passive components required to meet the transient requirements of the output capacitor. The MAX15301 can be configured as a stand-alone or in a multiphase solution.

The MAX15301 digital controller, however, features a proprietary auto-adjustment feature that simplifies design. Now the user does not need an engineer to compensate the power supply and can be assured of optimal compensation. Telemetry integration also reduces the need for external ICs, allowing for more dense designs.

Summarize

Base station power supply designers must make tradeoffs between size, efficiency, and performance. New power supply solutions based on digital telemetry are simpler, flexible, and scalable. Base station systems designed around the MAX15301 will be more integrated and flexible. Constant component monitoring can be optimized and overall performance more reliable. Finally, digital telemetry makes juggling trade-off challenges simpler.