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Digital Power-Supply Controller/Monitor with PMBus Communication

  SUNNYVALE, CA -Maxim Integrated Products (NASDAQ: MXIM) introduces the MAX8688, the first chip to convert an all-analog power supply to a fully programmable, digital power-management solution. A complete digital power-supply controller/monitor, the MAX8688 uses PMBus™ for communication, and can be used to control/monitor up to a total of 127 power supplies on a single bus. The MAX8688 taps into existing analog power-management solutions to provide unequaled control and monitoring capabilities, all functionality previously only available in all-digital power supplies. The 'intelligence' behind the Company's new PowerMind™ family of products, the MAX8688 provides many major benefits including simplicity of design, lower cost, and unmatched accuracy.

High-Performance Applications Demand Digital

The electronics industry is expending considerable effort to go completely digital, as quickly as possible. The new requirements of high-performance systems like servers, switches, and routers force power supplies to have some intelligence. Intelligence can mean flexible monitoring, intelligent setting of warning and fault thresholds and fault handling, or microsecond resolution of timing events like tracking and sequencing. These high-performance applications also require a multitude of voltage rails on a given card or system. Numerous voltage rails present difficult sequencing and tracking tasks, almost impossible in the analog domain. Additionally, monitoring and understanding the status of power supplies, up to now only possible with multiple discrete components, can dramatically improve system reliability and reduce down time.

Systems used in financial institutions and global communications are expected to have zero downtime. Operating 24/7 is only possible with accurate monitoring, intelligent power management, redundancy, and decision-making in fault conditions. Prior to the PowerMind technology in the MAX8688, such intelligence in power management was either impossible, or only possible through completely digital, although still limited, power supplies.

PowerMind Technology Eases Analog's Transition to Full Digital

The MAX8688 facilitates the monitoring and control of the power supply by simply tapping into the existing, all-analog power supplies. The MAX8688 closes a slow loop around the power supply to bring utmost accuracy and control in setting the output voltage. By tapping into the enable, feedback node, and/or reference input, the MAX8688 provides unmatched tracking, sequencing, and fine setting of the output voltage down to ±0.2% accuracy over the operating temperature. Because the MAX8688 is in full control of the output, tasks like margining up or down and transitioning the output voltage at a controlled rate are quite simple. The MAX8688 uses the high accuracy of its integrated 12-bit, highly linear ADC to monitor output voltage, current, and on-board temperature. Consequently, multiple warning and fault thresholds are set and served with the flexibility of digital control.

In the PowerMind approach, a master microcontroller communicates to the MAX8688 through the PMBus. The system controller facilitates data logging and system-level control. Although the MAX8688 holds all the power supplies' peak temperature, output current, and output voltage data, the system controller can poll each power supply at fixed intervals and log the information intelligently for future analysis. For the first time, system integrators will have indispensable status and event information when they must research a problem and debug field failures.

The MAX8688 can also modify the performance of the power supply remotely-another unique benefit of PowerMind technology. Too often, system integrators must rush designs without full evaluation and characterization of the system before the first units ship to the field. Engineering judgment thus replaces actual data. This process poses performance risks, and does not always produce favorable results. This is especially true when a new ASIC is developed using the latest and smallest geometry process to achieve the highest clock speed. These ASICs generally have tight tolerances; there is a very fine distinction between too high a voltage that damages the part, and too low a voltage for data integrity. Finding this correct voltage is not a simple task, and typically would require characterizing multiple manufacturing lots. A MAX8688 system can prevent field failures and potential recalls by simply allowing remote access to the unit for programming the output voltage down to 500 µV steps, and/or the sequencing, the tracking, and the fault/warning thresholds. One can easily see how this remote access and control can help save millions of dollars and avoid potential litigation.

Current sharing between modules is also possible with the MAX8688 controller, because the system controller has both the information about the output current and full control of output voltage. By simply manipulating the output voltage of the slave module(s), the output current can be matched to that of the master module, regardless of the physical distance between the power supplies. This is generally a very difficult task, especially when the power supplies are physically far apart, as with high-power redundant power supplies.

The PowerMind approach with the MAX8688 keeps the PWM in the analog domain. Thus this migration to digital remains as simple as possible with no new tricks, new compensation methods, or jittery output, all of which are commonly associated with digital PWM. Although some argue that digital PWMs provide higher efficiency, faster transient response, and lower EMI, no factual data support this.

Easy-to-Use Software Converts Legacy Analog Systems to Digital

A graphical user interface (GUI) is supplied free of charge with the part. With no knowledge of digital control theory or how to write software/firmware, any engineer can use this GUI and the MAX8688 to implement a digitally programmable power supply. This is a great benefit to engineers and system integrators that do not want to discard legacy designs and risk a completely new architecture.

Using the Company's MAXQ2000 microcontroller as a system controller, the GUI writes the necessary firmware, which can be loaded in the flash memory and run on the microcontroller. On power-up the microcontroller loads the necessary register of the MAX8688 to work specifically as intended. This performance is repeatable and independent of component tolerances and lot-to-lot variations, which cannot be said for all analog solutions.

The user-programmable registers can also be stored in a low-cost, SOT23, 1kb EEPROM so that at power-up, the MAX8688 automatically fetches the data and loads the registers without requiring a system controller. This latter capability is particularly useful when controlling power in a module or in smaller systems without a system controller. The module manufacturers can load the MAX8688 with default values, which can then be over-written by the end user. This can also help with smaller systems in which a few power supplies are to be tracked/sequenced and controlled, but monitoring is not necessarily important. In these applications no system controllers are needed; the MAX8688 can start up on its own, and be self-supporting with preprogrammed parameters.

The MAX8688 is available in a space-saving, lead-free, 24-pin, 4mm x 4mm TQFN package. It operates over the -40°C to +85°C industrial temperature range. The MAX8688 requires a 3.3V ±10% supply voltage, and can control output voltages from 0 to 5.5V. Prices start at $1.95 (10k-up FOB USA). A preassembled MAX8688 EV kit is available to reduce design time.

Lunes, 19 Junio, 2006 - 12:03
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