Adaptive ICs optimize dc/dc-converter efficiency over wide load range
By Margery Conner, Technical Editor -- EDN, February 25, 2008
It can be a straightforward task to design a power supply for high efficiency at a single load point. Designing for high efficiency over a wide load range is a significant challenge, however. Organizations such as Energy Star specify minimum-efficiency levels of 100, 50, and 20% of full load for the ever-increasing minimum efficiencies that telcom and data-center computers require. Addressing this need, Zilker Labs’ new ZL2004/2006 digital-dc power controllers use proprietary algorithms to optimize converter efficiency over changing loads. Like the earlier versions of the converter family, the ZL2004/2006 features a digitally closed PWM (pulse-width-modulated) control loop. These control-loop algorithms result in a full-load efficiency improvement as great as 3% and a light-load efficiency increase greater than 15% in typical applications, thus reducing peak power dissipation by as much as 20%. The chips automatically adapt their performance characteristics to increase the operating efficiency of the system when the load drops without sacrificing peak efficiency at heavy loads at which thermal concerns become important. The ZL2006 integrates 3A MOSFET drivers that can support loads in excess of 40A; The ZL2004 requires external drive MOSFETs.
In addition to the adaptive-load algorithms, the ZL2004/2006 includes adaptive-diode emulation: As the load current falls, traditional synchronous step-down converters begin to sink current to maintain regulation, drawing current from the output capacitor and reducing efficiency. The ZL2006 and ZL2004 detect this point and prevent the lower MOSFET from turning on and pulling current from the capacitor, resulting in a 5to 10% efficiency improvement at load currents of less than 1A. Another of the chips’ means of increasing efficiency at light load levels is to reduce the operating frequency within a predefined range based on load-current changes.
For higher currents, you can parallel multiple devices in a multiphase configuration to achieve higher total load current than a single chip can support. As load demand decreases, the ZL2004/2006 can automatically optimize efficiency over the entire load range by turning off one or more phases in response to the load. Multiple devices can communicate through the single-pin digital-dc bus for nonhosted control of current-sharing and phase-sequencing. For a hosted power-management configuration, the chips also support PMBus commands.
The ZL2006 has a 3 to 14V input range and a 0.54 to 5.5V output range and is available in a 6×6-mm, 36-lead QFN package. The ZL2004 has a 3 to 16V input range and a 0.54 to 4V output range and is available in a 5×5-mm, 32-lead QFN package. Prices start at $2.95 (1000).
Zilker Labs¸ www.zilkerlabs.com.
