Sunnyvale, Calif.—Maxim Integrated Products' MAX8688 digital power supply IC works with any analog power supply to provide full control and monitoring.
In a quickly-evolving philosophy for digital power designs that's coming to exploit the best of both the analog and digital domains, Maxim's MAX8688 serves in the digital feedback loop (now the defining element of a digital-power design) for intelligent control, i.e., fine setting of output voltage, sequencing, tracking, margining and monitoring the status of the power supply. To facilitate that control, the MAX8688 is designed to simply tap into the enable, feedback, and reference inputs of the existing analog power supply.
The MAX8688 closes a slow loop around the power supply and can fine tune the supply's output to ±0.2 percent accuracy over the operating temperature. The chip also monitors supply current and onboard temperature using a 12-bit, highly linear A/D converter to set multiple warning and fault thresholds as required. The chip's PMBus interface facilitates data logging for system current, voltage, and temperature for system-level control as well as failure analysis.
The MAX8688 also has remote-programming capabilities to aid in system evaluation before the first few units have shipped to the field. In this role, the MAX8688 can set output voltage in 500 microvolt steps to, for instance, characterize the performance of an ASIC and to check sequencing, tracking, and fault/warning thresholds. At the same time, it can remotely program current-sharing levels for one or more power modules. Retaining the benefits of analog PWM circuitry, the MAX8688-based system requires no additional compensating networks.
Indeed, the capability of a digital PWM (when used) for higher efficiency, transient response and lower EMI is often overstated. With the additional time required to perform a D/A conversion, and digital quantization errors associated with setting output voltage, analog circuitry is likely a better choice. Fast response circuitry for over-current and over-voltage are also best done in analog.
Maxim provides a graphic user interface (GUI), allowing any designer to implement a MAX8688-based system without any knowledge of digital control theory or how to write software/firmware. Using a MAXQ2000 as a system controller, the GUI writes the necessary firmware, which can be loaded in the flash memory used to run the microcontroller. On power-up, the microcontroller loads the appropriate registers of the MAX8688. This operation is repeatable and independent of component tolerances and lot-to-lot variations, as opposed to analog solutions. For smaller power supply systems where monitoring is not a critical parameter, the user-programmable registers can also be stored in a low-cost, 1-kb EEPROM such that at power-up, the MAX8688 can automatically fetch the data and load the registers without the use of a system controller.
Click here to request the controller's full datasheet. The MAX8688 is available in a lead-free, 24-pin, 4-by-4 mm TQFN package and operates over the –40 to +85°C extended temperature range. Prices start at $1.95 (1000-up FOB USA). A preassembled MAX8688 EV kit is available to reduce design time.
Maxim Integrated Products, 1-800-998-8800, www.maxim-ic.com