SI9140 Datasheet, PDF (13/15 Pages) Vishay Siliconix – SMP Controller For High Performance Process Power Supplies

Si9140
Vishay Siliconix
The transition from stop clock and auto halt to active mode is
a perfect example. The microprocessor current can vary from
0.5 A to 10 A or greater during these transitions. If the
converter were to operate in discontinuous current mode
during the stop clock and auto halt modes, the transfer
function of the converter would be different compared to
operation in the active mode. In discontinuous current mode,
the converter bandwidth can be 10 to 15 times lower than the
continuous current mode (Figure 8). Therefore, the response
time will also be 10 to 15 times slower, violating the
microprocessor’s regulator requirements. This could result in
unreliable operation of the microprocessor.
FIGURE 7.
For these reasons, synchronous rectification is a must in
today’s microprocessors power supply design. Pulse-
skipping modes are undesirable in high-performance
microprocessor power supplies, especially when the minimum
load current is as high as 500 mA. This pulse-skipping mode
disables the synchronous rectification during light load and
generates a random noise spectrum which may produce EMI
problems.
Siliconix’ TrenchFET™ technology has resulted in 20-mΩ
n-channel (Si4410DY) and 35-mΩ p-channel (Si4435DY)
MOSFETs in the SO-8 surface-mount package. These
LITTLE FOOT® products totally eliminate the need for an
external heatsink.
FIGURE 8. Non-Synchronous Converter BW
FaxBack 408-970-5600, request 70026
www.siliconix.com
S-58034—Rev. G, 15-Mar-99
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