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Manage circuit board power with PLDs

Posted: 16 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:circuit board design? programmable power management? power management device?

If the use of single-function power management ICs was ever manageable, that time is past. Most circuit boards now typically use several multi-voltage devices, each with a power sequencing requirement. Devices with smaller transistor geometries require lower power supply voltage with increased current. Designers are often required to use one point of load supply per multi-voltage IC. Consequently, the number of power supplies used in a circuit board is increasing. With the increase in the power supply rails and the need for multiple sequencing arrangements, power management has become more complex.

As circuit boards become more complex, the traditional power management solution become more unwieldy. Today, a designer implementing power management functions with traditional single-function ICs either has to sacrifice monitoring some of the power supplies or use multiple single-function devices for each of the power management functions. Neither alternative is acceptable.

Increased circuit board area, reduced reliability!The growing number of single-function ICs and their associated interconnections not only increases the circuit board area, it statistically reduces the reliability of a board.

Second sourcing, compromised design!If single-function devices are selected from different vendors, there is an increased risk of production delays if even one component is not available. This results in second sourcing. However, second sourcing reduces the components available to the design engineer, forcing the designer to compromise the circuit board's fault coverage.

Increased system cost!The cost of assembly and testing increases proportionately with the number of components used in a system. The cost of a component is inversely proportional to the number of units procured. Because there are many components required in a given system, fewer components of each type are required to build that system, increasing the overall system cost.

TTL to PLD analogy
The use of multiple single-function IC devices to implement traditional power management solutions is reminiscent of the 1980s, when digital designers used TTL gates to implement logic functions. As circuit board complexity increased, designers were forced to choose either a fixed function ASIC or to increase the number of TTL devices used on a circuit board. Not surprisingly, the number of TTL devices used for system design increased rapidly.

The advent of PLDs enabled engineers to implement more functions in a given unit area of the circuit board while also reducing time-to-market. Managing fewer PLDs was a lot easier than managing a large number of TTL gates The number of components used in a system was reduced, resulting in a lower overall system cost. The same PLD could be used across multiple designs, reducing the number of devices used in a system. Companies could standardize on a few PLDs without compromising the functionality required for each circuit board. Designers could simulate the design in software before committing it to the circuit board, increasing the likelihood of first time success.

Today, using single-function power management ICs is analogous to yesterday's use of TTL gates. The design of today's complex circuit boards requires a power management PLD.

Programmable solution
A programmable power management device requires programmable analog and digital sections to facilitate integration of multiple traditional single-function power management devices.

A designer can configure the programmable analog section to monitor a combination of supply voltages without resorting to using a configuration-specific, factory-programmed single-function device.

The programmable digital section of the power management device is required to define the board-specific logic. The board-specific logic combines the results obtained from the programmable power supply monitoring section to implement reset generation, power supply fault interrupt generation and the sequencing of individual supplies. A programmable, software-based design methodology enables the power management device to provide a breadth of board-dependent power management functions.

Device example
An example of a programmable power management solution is Lattice Semiconductor's Power Manager II device. It integrates several programmable digital and analog sections to enable integration of multiple single-function power management devices. The figure is a block diagram of a Power Manager II device, the Power1014A. It is one of several members of the Power Manager II family.

The device monitors up to 10 supplies for over voltage and under voltage conditions using 20 on-chip programmable threshold precision comparators. Typical monitoring precision is 0.3 percent. The digital monitoring inputs can be used to interface with digital signals such as manual reset in, power supply and shutdown.

Shown is the block diagram of Power1014A, which integrates several programmable digital and analog sections to enable integration of multiple single-function power management devices.

Integrating power management functions into a single programmable power management device and using the same device across multiple boards offers these advantages:

Reduced board space, increased reliability!One of the main advantages of integrating multiple single-function ICs into one device is reduced circuit board area. Reducing the number of components and associated routing results in decreased circuit board area and associated cost. Statistically, reducing the number of components also results in increased circuit board reliability.

Meeting complex power management requirements!The number of power supplies used in today's circuit boards is increasing. Furthermore, the complexity of the monitoring and control functions is also increasing. Because programmable power management devices integrate more power monitoring inputs (compared with single-function ICs) and programmable digital logic section, these devices are better suited for implementing complex power management functions. In addition, programmability offers the flexibility to adapt quickly to changing specifications.

No need for second sourcing!Second sourcing typically has been a requirement in order to prevent a manufacturing delay due to the unavailability of a device. This requirement is magnified by the fact that a typical system will require multiple small single-function devices from multiple vendors. By standardizing on a single programmable power management device across all boards and projects, time consuming and resource draining second sourcing can be drastically reduced or even eliminated.

Reduced overall system cost!Programmable power management devices are typically less expensive than the sum of the cost of individual single-function ICs. In addition, standardization of power management across multiple circuit boards in a system further reduces cost due to increased volume purchase discounts.

Power management functions can be implemented in software!Designs are implemented in programmable power management devices using software. Typically, the software design tools also enable verification of power management algorithms using the on-board simulators. Because power management designs are verified fully before committing them to the circuit board, the chance of first-time success is high, which further shortens time-to-market.

- Shyam Chandra
Product Marketing Manager
Lattice Semiconductor Corp.

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