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Figure 1: Simplified functional circuit schematic of a COT buck
(step-down) switching regulator
Figure 2. The QFN package used
for Exar’s XR79106 power module
provides pads that ensure excellent
thermal conductivity
voltage and switching frequency,
and provide protection against over
current and over voltage conditions.
5. Ideally require no external
compensation - this can otherwise
be a time consuming task to ensure
design stability over worst-case
conditions of input/output voltages
and load currents.
6. Provide a solution that can fit in
tight spaces without compromise.
7. Achieve “plug-and-play” simplicity,
requiring no system troubleshooting
once the PCB is properly designed.
8. Achieve all of the above objectives
at a low cost in medium to large
volumes.
The significance of these points
can be appreciated by considering
a modest subsystem that needs to
provide five rails with output voltages
ranging from 0.6V to 3.3V and operate
from an input voltage of 5V 20V. A
buck (step-down) DC-DC converter
might typically be used to generate
each of these rails, as illustrated by
the simplified functional schematic
in figure 1. But, implemented as
a discrete solution, such a design
can easily take from two to four
months, with a good part of the time
spent ensuring that the stability of
the control loops and the resulting
transient response of the outputs can
be unconditionally guaranteed over
worst case temperature conditions
and across the 6 sigma distribution
of discrete component parameter
values. This length of time, in some
cases, can make or break the chance
of a new product making it to market
ahead of the competition.
Greater integration helps
22 l New-Tech Magazine Europe