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but is trumped by a
module
Today
many
semiconductor
companies provide DC-DC converter
solutions that integrate many of
the control elements of a switching
regulator, such as the compensation
amplifier and the ramp generator
and comparator, which form the
pulse-width modulator that controls
the power switch. However this still
leaves the MOSFET, LC output filter
and most of the passive compensation
feedback components off-chip. These
components need to carefully chosen
and their operation modeled, which
even using the design tools many
vendors offer is still time-consuming.
Far better, especially for system
designers who are not power
experts, is to use power modules
that integrate the PWM controller,
MOSFET power switches and
inductor in a single small form-factor
package. These modules are typically
designed, optimized and tested by a
multi-disciplinary team of engineers
who are each experts in their own
field. Consequently this provides
the application design engineer
with a device that delivers superior
performance, high reliability and
the benefit of immediate availability,
cutting down the time to market by
several months.
Good examples of these devices
are the latest members of Exar’s
expanding family of modules; the
XR79103/06 and XR79203/06 deliver
3A and 6A outputs at voltages down
to 0.6V from input supplies of up to
22V and 40V respectively.
What do these modules
offer?
Implemented as synchronous step-
down buck converters, these power
modules employ a proprietary
emulated current-mode Constant On-
Time (COT) control loop. They require
no external loop compensation and
are unconditionally stable using
ceramic output capacitors and
operate at near-constant switching
frequency, requiring very few
external housekeeping components.
The wide input voltage range allows
the XR79103/06 to operate from
industry standard 5V, 12V and 19.6V
rails while the XR79203/06 can cope
with standard 24V and 18-36V DC
rails, and also rectified 18VAC and
24VAC rails.
Consequently these modules not
only fulfill the earlier wish list, which
Figure 3. Thermal derating curve for Exar’s XR79106 power
module at VIN = 12V
Figure 4. Power modules require just a few external housekeeping
components and full details of how to calculate the values of
these are provided in the datasheet
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