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Solution converts analog power supply to digital

Posted: 20 Jun 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Maxim? MAX8688? power supply controller/monitor? PMBus?

Maxim Integrated Products has introduced the MAX8688, touted to be the first chip to convert an all-analog power supply to a fully programmable, digital power-management solution. According to the company, the device is a complete digital power-supply controller/monitor that uses PMBus for communication, and can be used to control/monitor up to a total of 127 power supplies on a single bus.

The device taps into existing analog power-management solutions to provide control and monitoring capabilities, all functionality previously only available in all-digital power supplies, Maxim said. The 'intelligence' behind the company's new PowerMind family of products, the device provides simplicity of design, lower cost and unmatched accuracy.

The new device facilitates the monitoring and control of the power supply by simply tapping into the existing, all-analog power supplies. It 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 device provides tracking, sequencing, and fine setting of the output voltage down to 0.2 percent accuracy over the operating temperature. Because the device 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, Maxim said. The device uses its integrated 12bit, 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 device 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 company said.

According to Maxim, the device can also modify the performance of the power supply remotelya unique feature 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. Maxim said 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 V steps, and/or the sequencing, the tracking, and the fault/warning thresholds.

Current sharing between modules is also possible with the new controller, said Maxim, 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.

Maxim supplies a GUI free of charge with the part. With no knowledge of digital control theory or software/firmware writing, any engineer can use this GUI and the MAX8688 to implement a digitally programmable power supply. Using the Maxim's MAXQ2000 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 new device 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, 1Kbit EEPROM so that at power-up, the device 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 device 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 device can start up on its own, and be self-supporting with preprogrammed parameters.

The device is available in a Pb-free, 24-pin, 4-by-4mm TQFN package. It operates over the -40C to 85C industrial temperature range. It requires a 3.3V 10 percent supply voltage, and can control output voltages of 0-5.5V. Prices start at $1.95 (10,000-up FOB USA). A preassembled MAX8688 EV kit is available to reduce design time.




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