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SMM665,
605, 205, 105 Supply Voltage
Marginers and Active DC Output
Controllers
COMPONENT SELECTION FOR OPTIMUM
PERFORMANCE
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Download
this entire
Applications
Note in PDF
format.
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Introduction
The SMM665,
SMM605, SMM205
and SMM105
Supply Voltage Marginers and Active DC Output
Controllers (ADOC) require proper external
component selection to achieve best performance
(Figure 1). The following discussion and formulae
provide the design engineer the guidelines to
obtain this performance. The values found may be
used with DC-DC converters, LDOs and on-card
converters.
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COMPONENT
SELECTION
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Choosing
the CTRIM_CAP Value
The value of the CTRIM_CAP
determines both the time required to
Margin the converter's output voltage and
the amount of output ripple voltage
induced by the ADOC function. To find the
value of the CTRIM_CAP that
minimizes output ripple voltage while
keeping the MARGIN settling time as short
as possible, first find the converter's
output voltage gain from its TRIM pin
input:
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where:
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For
example, a typical converter with
a nominal output voltage of 3.3V
is found to have a voltage gain
of:
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Note:
See "Setting the Value of
RTRIM (Figure 2)" for
determining AV for discrete PWM
controller
circuits.
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Figure 1
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The
converter ripple voltage induced
(caused) by the ADOC function
is:
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where:
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Rearranging
Eq. 2 to solve for the
CTRIMCAP
value:
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Choose
a 100uV output ripple voltage for
the 3.3V converter:
Insert this value into Eq. 4 to
find the CTRIMCAP
value:
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 Figure
1: The ADOC function Controls DC-DC
Converters via the TRIM pin. The
CTRIM_CAP and RTRIM
component type and values should be
determined for best operation. The
RTRIM resistor is not necessary
for DC_DC converter modules that have an
on-board Trim Resistor.
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SUMMIT
Microelectronics, Inc. reserves the right
to make changes to the products contained
in this publication in order to improve
design, performance or reliability. SUMMIT
Microelectronics, Inc. assumes no
responsibility for the use of any circuits
described herein, conveys no license under
any patent or other right, and makes no
representation that the circuits are free
of patent infringement. Charts and
schedules contained herein reflect
representative operating parameters, and
may vary depending upon a user's specific
application. While the information in this
publication has been carefully checked,
SUMMIT Microelectronics, Inc. shall not be
liable for any damages arising as a result
of any error or omission.
SUMMIT Microelectronics, Inc. does not
recommend the use of any of its products
in life support or aviation applications
where the failure or malfunction of the
product can reasonably be expected to
cause any failure of either system or to
significantly affect their safety or
effectiveness. Products are not authorized
for use in such applications unless SUMMIT
Microelectronics, Inc. receives written
assurances, to its satisfaction, that: (a)
the risk of injury or damage has been
minimized; (b) the user assumes all such
risks; and (c) potential liability of
SUMMIT Microelectronics, Inc. is
adequately protected under the
circumstances.
Revision 1.1 - This document supersedes
all previous versions. Please check the
Summit Microelectronics, Inc. web site at
www.summitmicro.com
for updates.
I2C is a trademark of Philips
Corporation.
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Copyright
© 2003 SUMMIT MICROELECTRONICS, Inc.
Power Management for Communications™
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