|
|
|
SMM105/205/605/665
ADOC Tutorial and Performance
Summary
|
|
|
|
SMM105
CONTROLS A HIGH CURRENT
LDO
|
|
In
addition to controlling DC-DC converters, the ADOC
function can be used with any device having an
access point for changing the output voltage such
as a 'VFB' or 'VADJ' pin. In Figure 3, the FB input
(pin 4 of the Adjustable LDO) is connected to the
SMM105's TRIM pin through a series 2.5k resistor
(R8). The value of R8 is critical to limit the
Margin voltage and to otherwise prevent too large a
change from occurring on the LDO output from the
maximum voltage swing on the TRIM output
(approximately 0V to VDD_CAP). See App
Note 37
for calculating this
value.
|
|
|
Figure
3: ADOC Controls a High-Current LDO Fed by
a Switch-Mode DC-DC Converter through the
FB pin.
|
|
|
TEST SETUP
The complete circuit displayed in Figure 19 was
built to obtain performance results using both a
DC-DC converter alone and an LDO supplied by the
converter. The following tests were performed and
measurements recorded:
|
|
1.
|
Step
load response of the 1.8V LDO circuit with
and without the ADOC function
enabled.
|
|
|
2.
|
Step
load response of the 3.3V DC-DC Converter
with and without the ADOC
function.
|
|
|
3.
|
Output
Ripple voltage of the 1.8V LDO circuit
with and without the ADOC
function.
|
|
|
4.
|
Output
Ripple voltage of the 3.3V DC-DC converter
with and without the ADOC
function.
|
|
|
5.
|
Margin/TRIM
DC performance of the 1.8V LDO with and
without the ADOC function (loaded and
unloaded).
|
|
|
6.
|
Margin/TRIM
DC performance of the 3.3V DCDC converter
with and without the ADOC function (loaded
and unloaded).
|
|
|
|
|
|
|
|
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.
|
|
Copyright
© 2003 SUMMIT MICROELECTRONICS, Inc.
Power Management for Communications™
|
|
