advertisement High Performance Power Solutions for AMD Opteron
and Athlon 64 Processors – Design Note 326
Henry J. Zhang and Wei Chen
Introduction
AMD Opteron and Athlon 64 CPUs can draw 65A at very
low voltages (0.8V to 1.55V). Such high currents put efficiency and related thermal issues at the top of a power
supply designer’s list of problems. The new LTC ®3733
PolyPhaseВ® synchronous buck controller solves these
problems, and others, by enabling solutions that offer
high efficiency, low profile and fast transient response. inductor size. The LTC3733’s integrated MOSFET drivers
also simplify the design and minimize the overall supply
footprint. The LTC3733 directly senses the inductor
current of each phase to achieve excellent current
sharing among phases, thus evenly distributing the
thermal stress. As a result, overdesign of the MOSFETs
and inductors is unnecessary and the circuit can be
operated reliably without a heat sink. The total size and
cost of the solution is minimized. The LTC3733 is a 3-phase current mode controller that
drives three synchronous buck stages 120В° out of phase.
The three out-of-phase stages inherently self-cancel the
current ripple and thus minimize the size of the input
and output capacitors. Likewise, ripple cancellation
and a high switching frequency (up to 600kHz) make it …