PCB Blog - Programmable power management scheme for PCB board design

PCB board power management is generally concerned with all aspects involved in powering a PCB board. Some commonly covered issues are:

1. Select various DC-DC converters to supply power to the PCB board;

2. Power on and off sequencing/tracking;

3. Voltage monitoring.

In this article, power management is simply defined as managing all power on the PCB board (including DC-DC converters, LDOs, etc.). Power management includes the following functions: managing the DC-DC controller on the PCB. For example, hot-plug, soft-start, sequencing, tracking, tolerance, and regulation; all relevant power states and control logic signals are generated. For example, reset signal generation, power failure indication (monitoring), and voltage management. Figure 1 demonstrates a typical power management function on a PCB with a CPU or microprocessor; the hot-plug/soft-start control function is used to limit inrush current to reduce the start-up load on the power supply. This is an important function for PCB boards that are inserted into active substrates; power sequencing and tracking functions are used to control how to turn multiple power supplies. Fault (over/under voltage) monitoring of all voltages to warn the processor of impending power failure. This function is also known as the "supervisory function". The reset generation function provides a reliable start-up condition for the processor when the processor is powered up. Some processors require the reset signal to remain for a period of time after all operating power sources of the processor are stable. This is also known as reset pulse stretching. The function of the reset generator is to keep the processor in reset mode in the event of a power failure to prevent undesired errors in the on PCB board flash memory

1. Limitations of traditional power management solutions

Traditionally, each power management function on the PCB is implemented by a separate functional IC. These ICs are available in different models for different voltage combinations. In this way, there are hundreds of single-function IC models from different manufacturers to meet different power management needs. For example, to select a reset generator IC model, the following information must be provided:

1) The number of voltage channels to be monitored by the reset generator IC;

2) A combination of voltages (3.3, 2.5, 1.2 or 3.3, 2.5, 1.8, etc.);

3) % of fault detection voltage (3.3V-5%, 3.3V-10%, etc.);

4) Accuracy (3%, 2%, 1.5%, etc.);

5) The reset pulse extension function is controlled by an external capacitor;

6) Manual reset input.

To handle all possible variations of these parameters, there can be hundreds of models from one manufacturer alone for a single reset generator IC. Also, if the engineer needs to monitor another voltage (probably) during the design process, a different model must be selected. Similarly, many single-function ICs are available in many variants based on different parameters, even for the same function, such as hot-swap controllers, power sequencers, and voltage monitoring/detector function ICs. A different set of these single-function ICs is required for each PCB board of a system consisting of multiple PCB boards, thereby also increasing the bill of materials.

2. The complexity of PCB board design continues to increase

If the use of single-function power management ICs was ever manageable, it's a thing of the past. Many PCB boards now typically use several multi-voltage devices, each with a different power-up sequence. Devices with finer process nodes require lower voltages but higher currents. Designers often need to utilize one point of load per multi-voltage power IC. In this way, the number of power supplies used on the PCB will increase. Power management becomes more complex as supply voltage loops increase and multiple sequencing management is required. As PCB board designs become more complex, traditional power management solutions become more difficult to handle. Currently, designers implementing power management with traditional single-function ICs either have to forego monitoring certain voltages or use multiple single-function devices for each power management function. Neither of the following two methods is advisable.

1) Increase the PCB area and reduce the reliability

The increase in the number of single-function ICs and the consequent interconnection between them not only increases the PCB area but also reduces the reliability of the PCB from a statistical point of view. For example, it is possible to increase the probability of assembly errors, leading to unforeseen (certainly bad) results.

2) Second supply channel and design compromise

When single-function devices are purchased from different suppliers, there is an increased risk of production delays due to even one of the devices not arriving on time. This in turn leads to the need for a second supply channel. However, the second channel reduces device availability for the design engineer, forcing designers to sacrifice fault monitoring coverage on the PCB due to these out-of-reach devices. Assembly and test costs are proportional to the number of devices used in the system. The unit cost of the device is inversely proportional to the purchase volume. Since many devices are required in a given system, fewer of each device is required to construct the system, increasing the overall system cost. For example, assuming a system has 10 PCB boards, 1,000 such systems will be manufactured per year. If each PCB board uses a single-function IC for power management, about 10 different single-function ICs are required to complete the design. The annual demand for these single-function ICs is 1,000 pieces. The unit price in batches of 1,000 is of course higher than the unit price in batches of 10,000. Therefore, the cost of the former power management solution is definitely higher than that of using the same single-function power management IC for all PCB boards. Traditional power management schemes implemented with multiple single-function IC devices are a thing of the past in the 1980s when digital designers used TTL gates to implement logic functions. As PCB board complexity increases, designers have to choose between using a fixed-function ASIC or increasing the number of TTL gates used. Not surprisingly, the number of TTL devices used in system designs is increasing dramatically.

The advent of Programmable Logic Devices (PLDs) has enabled designers to achieve more functionality within a given PCB area and has also shortened the time to market. The overall system cost is also reduced by reducing the number of components used in the system. Because the same PLD can be used in multiple designs, the number of components used in the system is reduced. Companies can standardize on a small number of PLD devices without sacrificing the required functionality of each PCB board. It is much easier to manage a small number of PLDs than many TTL gates. The same PLD can be used for multiple PCB designs, reducing or even eliminating the need for a second supply channel. Designers can use software to simulate designs before they are pitched, increasing their chances of success. Currently, using single-function power management ICs is as old-fashioned as using TTL gates in the past. Designing today's complex PCB boards requires "Power Management PLDs". Indeed, the adoption of this device should now be an offer for PCB board design.

3. Programmable power management scheme

A typical PCB board power management implementation uses a single programmable power management device. Programmable power management devices require programmable analog and digital sections to simplify the integration of multiple traditional single-function power management devices. Designers can configure the programmable analog section to monitor a set of voltage combinations without resorting to a specially configured, factory-programmed single-function device. The programmable digital portion of the power management device is required to define logic for the PCB board that incorporates programmable power monitoring functions such as reset generation, power failure interrupts generation and sequencing of individual power supplies. A software-based programmable design methodology enables power management devices to provide multiple board-specific power management functions.

4. Programmability Standardizes Power Management

By simply reconfiguring the programmable device, designers can implement all board-specific power management functions with a single programmable power management device. The same programmable device can be used on multiple PCB boards instead of using multiple single-function ICs. As a result, designers can standardize on a single programmable power management device throughout the design. Consolidating power management functions into a single programmable power management device and utilizing the same device on multiple PCBs provides the following benefits:

1) Reduce the size of the PCB board and increase the reliability

The main benefit of integrating multiple single-function ICs into one device is reduced PCB board area. The reduced component count and corresponding interconnect traces reduce PCB area and cost. From a statistical point of view, the reduced component count also increases the reliability of the PCB.

2) Ability to meet complex power management needs

The number of power supplies used on PCB boards today is increasing. In addition, the complexity of monitoring and control functions is increasing. Because programmable power management devices integrate more power monitoring inputs (compared with single-function ICs) and programmable digital logic, these devices are more suitable for implementing complex power management functions. In addition, programmability provides the flexibility to quickly adapt to meet changing specification requirements.

3) No need for a second supply channel

In general, the second channel is a precautionary measure taken to circumvent production delays due to the unavailability of devices. This need is exacerbated by the reality that a typical system actually requires multiple small-scale single-function devices from different suppliers. By standardizing on a single programmable power management device across all PCBs and projects, the need for a time-consuming and resource-intensive second channel can be significantly reduced or eliminated altogether.

4) Lower overall system cost

Programmable power management devices are generally less expensive than the sum of individual single-function ICs. In addition, standardized power management is implemented for multiple PCB board in the system, which further reduces costs due to higher discounts due to larger batches.

5) The power management function can be realized by software

Designed using programmable power management devices implemented in software. Typically, the software design tool also supports the verification of power management algorithms used on the PCB board simulators. Because the power management design is fully verified before the board is launched, the chance of sexual passing is high, which further accelerates the pace of product launch.

The number of power supplies used on today's PCBs continues to increase, and power management algorithms become even more complex. However, traditional outdated power management schemes are still often used in these increasingly demanding applications, making PCB design inefficient and expensive, and often resulting in poor results due to unavoidable trade-offs. This paper presents a design for this complex power management problem: using programmable, mixed-signal power management devices. Designers can standardize on "power management PLDs" and use the device throughout the system PCB board, reducing cost, increasing reliability, and speeding up time to market.