[Technology Report]
Controller ICs Energize Power-Supply Design
New "do-it-yourself" controller and driver ICs give systems builders options to tackle the difficult task of providing power supplies for today's demanding equipment.
For the converter in the online schematic, targeted for inexperienced power designers, Fairchild provides Excel spreadsheets to assist in the design, demonstration boards (because layout is very important), schematics, a preferred layout, and engineering help from the staff.
TI offers a controller family for high-current dc-dc converter POL applications. The TPS4009x dc-dc buck controllers use PWM to manage two-, three-, or four-phase designs that support applications from 40 to 120 A. Each phase can provide an output current from 20 to 30 A.
A typical high-current, two-phase design (Fig. 3) includes a TPS4009PW controller. It drives a pair of external synchronous buck drivers that can be TPS2830 or TPS2834 adaptive gate drivers. The gate drivers, in turn, control the power MOSFETs, which are also external due to the high current to be provided. In a four-phase design operating at a switching frequency of 4 MHz, the ripple frequency will be 4 MHz, making filtering easier, more efficient, and less costly than at lower frequencies. An output voltage droop (pins 7 and 8) can be programmed to improve the transient window and reduce the size of the output filter.
The TPS4009x controllers provide system protection features, including current-sense fault, programmable overcurrent, and individual phase-current detection. An adjustable voltage threshold sets current limit up to 200 A. The company claims an efficiency of greater than 90% in step-down conversion application.
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