MIC5191

Micrel

April 2004

12

M9999-042804

Using the MIC5191 as a filter for a switching regulator

reduces output noise due to ripple and high frequency switch-

ing noise. It also reduces undershoot (Figure 12) and over-

shoot (Figure 13) due to load transients with decreased

capacitance.

Figure 13. Transient Response

Due to the high DC gain (80dB) of the MIC5191, 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.

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

loads. Not only do we have to contend with the tolerance of

the supply (line regulation, load regulation, output accuracy

and temperature tolerances), but the trace lengths create

additional issues with resistance and inductance. With lower

voltages these parasitic values can easily bump the output

voltage out of a usable tolerance.

Load

Load

Switching

Power

Supply

Circuit Board

Load

Load

Long Traces

Figure 14. Board Layout

But by placing multiple, small MIC5191 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 example, the MIC5191

will provide accurate 1V output, efficently and with very little

noise.

Figure 15. Improved Distributed Supplies

Load

Load

Switching

Power

Supply

Circuit Board

Load

Load

MIC5191

MIC5191

MIC5191

MIC5191

TIME (100

µs/div)