How to optimize base station systems using digital power

　　Base station power engineers face numerous design challenges. Wireless operators want them to reduce power consumption and system size. Subsystem power supply also requires certain complex tasks such as sequencing, monitoring, and margin adjustment. In order to meet the above application requirements to the greatest extent, designers must make various compromises to achieve a balance between power conversion efficiency and size, performance complexity and cost. This article introduces a new, highly integrated power solution that effectively optimizes system performance while providing system design flexibility, helping designers overcome the challenges they face.

　　Improve efficiency

　　The energy cost of base station operation is of great significance to wireless operators, and more efficient power supply solutions are needed to reduce operating expenses. In addition, the reduction in power consumption also helps with heat dissipation design, and operators can use smaller heat sinks in wireless units. The smaller the heat sink, the smaller the size of the unit circuit. Finally, since wireless units are usually installed on poles or on the side of buildings, reducing the overall size can minimize mechanical stress.

　　The baseband unit of a base station usually provides fast signal processing capabilities to handle the large amount of data and voice traffic in the network. The baseband unit requires high current, multi-voltage power supply, and the total power supply current may exceed 60A, which requires a multi-phase power supply solution and requires remote control capabilities. Techniques to improve power conversion efficiency include reducing conduction losses, switching losses, and reverse recovery losses. Conduction losses can be reduced by selecting MOSFETs with low on-resistance (RON); higher gate drive can also help reduce on-resistance (RRDSON), but higher switching voltage will increase switching losses to some extent. Nevertheless, it is best to select a settable gate drive function. When the load current is large, a higher gate drive voltage will reduce conduction losses; under light load conditions, the gate drive voltage can be reduced. Automatic selection can optimize the balance between conduction loss and switching loss, which is beneficial to base station power supply design.

　　The MAX15301 digital point-of-load (PoL) controller uses advanced algorithms to achieve the highest levels of conversion efficiency and transient response over the entire operating range. The device provides advanced high-efficiency, adaptive gate drive for external MOSFETs. The device optimizes power efficiency by continuously and adaptively adjusting load, voltage, and current.

　　Simplify power supply complexity and improve system reliability

　　If system parameters can be monitored, system performance can be better managed, thereby improving system reliability. As mentioned above, the baseband unit must have powerful signal processing capabilities to handle large amounts of data and voice traffic. During power-on/power-off, multiple power supplies with different currents/voltages must be turned on/off in the correct order. The current and temperature during baseband operation need to be monitored to ensure that the system operates within the tolerance range and provide alarm or fault indication signals when necessary. In addition, remote control functions and advanced fault management functions can ensure that the base station achieves higher reliability. If an analog solution is used, these functions will require the support of multiple devices and power management. The digital solution can reduce the design complexity and only requires an independent power management chip (as shown in Figure 1).

　　Base station power supplies often require very complex power management controllers, with multiple discrete components required for each function. The total board area and complexity of the design solution also increase accordingly. In addition, because base stations operate under extreme temperature conditions, the design solution must remain reliable over a wide operating temperature range. For traditional analog power solutions, compensation can only be set under a single operating condition, but the wide operating range problem must be solved. At the same time, differences in passive components (such as inductors and capacitors) also increase the complexity of power supply compensation.

　　Digital systems can be used as an alternative. Digital architectures can achieve automatic compensation and help optimize bandwidth. A wider bandwidth load transient response helps improve system tolerance or save output capacitors, thereby reducing system size. In addition, since passive device parameters change with temperature, the automatic compensation function can adaptively adjust to changes in conditions, thereby achieving optimal design over the entire temperature range.

　　Figure 1. System design for analog (left) and digital (right) approaches.

　　Digital solutions integrate power management for each DC-DC converter, creating a flexible and easily scalable system. Digital remote control continuously monitors system compensation to ensure optimal base station performance. Maxim InTune products, such as the MAX15301, solve the design challenges of power management. These products easily enable high-performance, DC-DC power supply designs with smaller filter capacitors and higher efficiency. This digital power technology is based on "state space" or "model predictive" control rather than proportional-integral-derivative (PID) control, which is used in most digital controllers. The automatic compensation process in the MAX15301 is based on measured parameters, which helps to build an internal mathematical model of the power supply, including external components, which ultimately makes the switching power supply have higher dynamic performance and ensure stable operation. The design uses multiple patented algorithms to optimize efficiency over a wide operating range.

　　Reduced board area

　　Since antennas may be mounted on buildings, towers or utility poles, system weight becomes a major concern, and there is an urgent need to reduce the board area of ​​wireless units, especially baseband units, where powerful digital processors occupy a very large board area. Integrated MOSFETs have smaller packages and can be used for point-of-load power supplies. This solution is feasible for low-power applications, but not suitable for high-current designs. Controller-based solutions allow for greater flexibility in optimizing the selection of MOSFET devices for specific operating conditions. This solution also helps to dissipate heat from the board and facilitate thermal management. Of course, external MOSFETs will increase the board area.

　　Since the baseband unit supply current can be as high as 60A/power supply, a multiphase conversion scheme is required. For these high current supplies, the number of passive components (capacitors in this case) needs to be increased to meet transient requirements. The MAX15301 can be configured for single-machine or multiphase operation. The MAX15301 digital controller uses a proprietary auto-adjustment technique that greatly simplifies the design. The engineer does not need to perform power supply compensation during the design, ensuring optimal compensation. The integrated remote control function also reduces the requirements for external ICs, which can support higher density designs.

　　Summarize

　　Base station power design requires careful trade-offs between size, efficiency, and performance. Maxim's new generation of power solutions based on digital remote control have the advantages of simplicity, flexibility, and easy adjustment. The power system designed with MAX15301 can provide higher integration and flexibility. Through continuous compensation monitoring, the overall performance is optimized. In addition, the digital remote control function makes the design balance and compromise simpler and more direct.