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SMM105/205/605/665
ADOC Tutorial and Performance
Summary
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Figure
2: The ADOC function simplified block
diagram.
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ACTIVE DC OUTPUT CONTROL (ADOC),
Cont'd
As far as loop stability is concerned, the ADOC
control loop is slow compared to the overall DC-DC
converter or LDO loop. Also, the incremental change
on the TRIM pin is small so the control loop
provides a unconditionally stable limit cycle. That
is, for all noise with amplitude greater then the
incremental change on the TRIM pin, the control
loop has a gain of less then one. For noise with
amplitude less than the incremental change on the
TRIM pin the control loop has a gain greater than
one. This noise is amplified until its' amplitude
is greater than the incremental change on the TRIM
pin where the control loop's gain is less than one
providing the stable limit cycle. The incremental
change on the TRIM pin is usually set to less than
500uV, so the amplification of noise below this
level is negligible. There are no stability
problems observed using the ADOC feature.
Margining
of the converter is an extended feature of the ADOC
function. The user programs the nominal; high and
low converter output voltages. During normal
operation the ADOC keeps the output voltage at the
nominal setting.
During the Margin event, the device gradually
increases the voltage on the TRIM_CAP each ADOC
cycle until the Margin point (high or low) is
reached. The time required for the Margin event is
selectable for a 'Slow' or 'Fast' margin time. The
Margin time is further affected by the value of the
TRIM_CAP (App
Note 37).
Note:
All control functions (ADOC, Margining) are
disabled when the 'Enable Control' (Figure 4)
button is unchecked.
Many applications require the high-efficiency
afforded by the DC-DC converter but cannot
withstand the high noise content. Such applications
often employ a DCDC converter followed by an LDO
(Low-Drop Out) linear regulator. Employing the
SMM105, the circuit in Figure 3 (the complete
schematic is displayed in Figure 19) was used to
test the performance of the ADOC and other features
of the SMM105 employing a 2.0V DCDC converter
followed by a high-current LDO. The external
N-channel pass MOSFET (Q1) is used to obtain a
high-current, low-noise 1.8V supply.
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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 1.0 - This document supersedes
all previous. 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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