MIC5190
Micrel
Using the MIC5190 as a filter for a switching regulator
reducesoutputnoiseduetorippleandhighfrequencyswitch-
ing noise. It also reduces undershoot (Figure 12) and over-
shoot (Figure 13) due to load transients with decreased
capacitance.
lower voltages these parasitic values can easily bump the
output voltage out of a usable tolerance.
Circuit Board
Load
Load
Load
Long Traces
Switching
Power
Supply
Load
Figure 14. Board Layout
TIME (100µs/div)
Figure 13. Transient Response
But by placing multiple small MIC5190 circuits close to each
load, the parasitic trace elements caused by distance to the
power supply are almost completely negated. By adjusting
the switching supply voltage to 1.2V, for our example, the
MIC5190 will provide accurate 1V output, efficiently and with
very little noise.
Due to the high DC gain (80dB) of the MIC5190, it also adds
increased output accuracy and extremely high load regula-
tion.
Distributed Power Supply
As technology advances and processes move to smaller and
smaller geometries, voltage requirements go down and cur-
rent requirements go up. This creates unique challenges
when trying to supply power to multiple devices on a board.
When there is one load to power, the difficulties are not quite
as complex; trying to distribute power to multiple loads from
one supply is much more problematic.
Circuit Board
Load
MIC5190
MIC5190
Load
If a large circuit board has multiple small-geometry ASICs, it
will require the powering of multiple loads with its one power
source. Assuming that the ASICs are dispersed throughout
the board and that the core voltage requires a regulated 1V,
Figure 14 shows the long traces from the power supply to the
ASIC loads. Not only do we have to contend with the toler-
ance of the supply (line regulation, load regulation, output
accuracy, and temperature tolerances), but the trace lengths
createadditionalissueswithresistanceandinductance. With
Load
MIC5190
Switching
Power
Supply
MIC5190
Load
Figure 15. Improved Distributed Supplies
December 2005
12
M9999-120105
MICREL [ MICREL SEMICONDUCTOR ]
