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SMM105/205/605/665
ADOC Tutorial and Performance
Summary
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Download
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Applications
Note in PDF
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INTRODUCTION
Summit Microelectronics' family of programmable
Active DC Output Control (ADOC) devices greatly
simplify and enhance the trimming and margining of
DC-DC converters and other adjustable power
supplies. Active output control permits a
±0.2% accurate setting of supply voltages when
using a ±0.1% external voltage reference. The
product family consists of a single channel device,
a dual channel device and a six-channel device with
or without sequencing. Test and performance results
using the SMM105
single channel ADOC are presented herein. These
results are attainable with any ADOC family member
including the SMM665/605
six channel devices and the SMM205
dual channel.
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ACTIVE
DC OUTPUT CONTROL
(ADOC)
Using the Trim pin to actively control a power
supply converter's output voltage can greatly
enhance system performance and reliability. The
converter may be an off-the shelf device or an
on-board design consisting of a monolithic
converter with associated circuitry. In both
instances, the ADOC function dramatically improves
voltage accuracy by implementing closed-loop active
control of the converter's output voltage.
ADOC is accomplished using the DC-DC's Trim pin
(Figure 1), or an output voltage adjustment (VADJ
or FB) node from the on-card converter (Figure 3).
The ADOC TRIM pin is connected to the converter's
Trim input. A sense line from the converters
point-of-load is connected to the corresponding VM
input.
The ADOC function cycle time is 2ms. Slight
adjustments to the converter voltage using the TRIM
output pin are made based on the voltage input on
the VM pin. This is compared to the internal
programmed setting and the converter's Trim pin and
to the output voltage gain polarity (Figure 2).
This adjustment controls the output voltage of the
power supplies to within ±0.2% when using a
±0.1% external voltage reference. The TRIM_CAP
is fed a current of 30uA for a period of 5µs
each ADOC cycle (2ms). The polarity of the current
depends on whether the converter's output is higher
or lower than the pre-programmed nominal voltage.
The voltage on the TRIM_CAP pin is buffered and
then driven out the TRIM pin to control the
converter's output voltage.
Voltage adjustments appearing on the TRIM pin cause
a slight ripple voltage to appear on the
converter's output. The magnitude of this ripple is
easily minimized (see App Note 37).
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Figure
1: The ADOC function Controls DC-DC
Converters via the TRIM
pin.
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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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