Benefits of Digital Power Management

New generation ICs require lower supply voltages, and a single device often uses multiple voltages that must be applied to the device in the correct sequence. These very low voltages to the IC must be generated on-board, with minimal voltage drop and regulated. Most on-board power systems use modular DC-DC converters as building blocks. High-performance DC-DC converter modules are suitable for a wide range of power supplies, either as isolated brick converters or as non-isolated point-of-load converters (POLs).

In these environments, power management functions are required to be integrated with the building blocks to form a complete working and robust power system. Power management includes: power system monitoring, sequencing and tracking, monitoring and failure protection. In fact, each function is isolated from the high current circuit of DC-DC conversion.

In a typical 48V power system using an intermediate bus (IB) and power management, a single brick converter generates the intermediate bus voltage, which is fed into a number of POL converters that provide each low voltage output rail. The brick converter also maintains isolation from the 48V input circuitry.

Guaranteed timing control

Potentia Semiconductor's PS-1006 power management device can be used on the 48V primary side to handle input start-up limit, start-up and shutdown control. Another power management device, the PS2406, is used on the secondary side to control start-up sequencing and output voltage regulation, and provide failure protection for overvoltage and undervoltage conditions. This dedicated digital power management device is much superior to the commonly used analog method or general-purpose microcontroller or PLD method.

The PS2406 can control all output rail voltages in real time, and its internal logic can protect startup and shutdown, following the required timing under all conditions. Sequencing does not rely on the power converter startup time or time delay circuit. The internal locking startup threshold prevents enabling a rail until the previous rail has started correctly. Failure management logic ensures that after a failure occurs, the remaining rails are still closed in time.

Digital Failure Detection

Overvoltage and undervoltage fault detection is usually based on multiple voltage sampling, using ADC and digital averaging to identify fault conditions and instantaneous voltage transients. This can improve system performance, quickly shut down in fault conditions and avoid incorrect shutdown. The ADC is selected for fast sampling, so that it can react to faults faster than general-purpose microcontrollers. Fault detection voltage thresholds and timing can be configured to suit the application.

The DC-DC converter regulation input is driven by a dedicated DAC within the PS-2406, under control of the device's I2C interface. This technique allows precise adjustment of settings and can be driven by system software. This makes it easy to implement software-based features such as long-term output voltage stability and automatic margin control.

All voltage thresholds are based on an internal reference with better than 0.5% overall accuracy, while time delays and digital filters derive timing values ​​from the device clock. Timing values ​​can be extremely precise, especially if the clock is controlled by a crystal or ceramic resonator.

The PS-2406's I2C interface allows the board controller to read all output voltages in real time, which enables comprehensive power system monitoring. If necessary, current shunts can be added and output current measurements can be made through the I2C interface. When the PS-1006 is used for primary management, the primary status can also be controlled through the secondary I2C interface. The PS-1006 can measure primary parameters and report status to the PS-2406 through an isolated PI-Link interface. These parameters include input voltage, output current, fuse status, input overvoltage, and brownout.

Once the design is approved, the same configuration files are used for all units during board assembly and test. Performance is consistent between units and does not vary, unlike in analog designs where component tolerances can cause variation.

Startup sequence

In any complex on-board power system, a significant portion of the overall design effort requires defining and implementing power management functions, which are required for control and monitoring of power converters. Power management functions include startup and shutdown sequencing and tracking, real-time voltage and current measurement and readout, fault protection, and output voltage adjustment control. Many applications require isolation between the primary and secondary parts of the power system, which complicates the design when remote readout of system voltage and current is required. In addition, when developing related products, especially when the power system is embedded on the circuit board, its requirements are bound to change significantly.

Traditional power system design relies on discrete analog circuits to implement power management functions, relying on amplifiers, comparators, and RC time delays to set parameters. As the design progresses, any changes require component changes and often require reworking of printed circuit boards. The use of dedicated digital power management devices allows operating parameters to be set through configuration software rather than circuit components. With this approach, parameters can be easily changed as needed during the design process without making hardware changes.

Configuration software

All PS-2406 functions are controlled using the associated PowerCenter Designer configuration software. The initial configuration of the power converter (power topology) and the required startup sequence are entered graphically through on-screen graphics and checkboxes.

Once the power topology is entered, the operating parameters (such as voltage levels, time delays, voltage adjustment settings, and GPIO pin functions) are configured on the parameter entry screen. Overvoltage and detection time parameters can be set separately for each rail. Overvoltage detection is also suitable for intermediate bus voltage detection. To further simplify the design process, all parameters are automatically set to typical default values ​​in the Power Center Designer software, and the designer only needs to fine-tune a few values ​​to suit the application.

When all parameters are entered as required, they are downloaded to the PS-2406 via the I2C port using a programming cable. If any parameters need to be adjusted during development, they can be edited and reloaded in just a few minutes without removing possible devices from the board.

If a general-purpose microcontroller is used for power management, custom software must be developed for each application, and implementation modifications are complex. Extensive testing is required to confirm the correct logical performance of the software under all functional and failure conditions.

With a device designed specifically for power management applications, its internal logic is predetermined, and only the configuration is changed to suit different applications. Changing the configuration takes only a few minutes without the need to develop and test any custom software. Specialized digital power management controllers can greatly improve the performance of end products and allow power system monitoring to be fully integrated into product management software.