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Texas Instruments Incorporated
High-Performance Analog Products
Analog Applications
Journal
Second Quarter, 2011
© Copyright 2011 Texas Instruments
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Texas Instruments Incorporated
IMPORTANT NOTICE
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Copyright © 2011, Texas Instruments Incorporated
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High-Performance Analog Products
2Q 2011
Analog Applications Journal
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Texas Instruments Incorporated
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Data Acquisition
The IBIS model, Part 3: Using IBIS models to investigate signal-integrity issues. . . . .5
TI is developing a new arsenal of digital input/output buffer information specification (IBIS) simulation
models to meet a variety of customer needs. This article, the third of a three-part series, shows how to
use an IBIS model to extract important variables for signal-integrity calculations and PCB design
solutions.
Power Management
Implementation of microprocessor-controlled, wide-input-voltage, SMBus
smart battery charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
For the utmost in system flexibility, using microprocessors to control Li-ion battery chargers is
becoming very popular. This article describes the design of a microprocessor-based charger that can
handle an input of up to 55 V and can supply an output charging voltage of 5 to 51 V at up to 10 A. Both
the hardware and software have been tested to aid designers in quickly prototyping their own solutions.
Benefits of a coupled-inductor SEPIC converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
The SEPIC topology provides a convenient solution when a converter must operate in both buck and
boost modes. While the SEPIC has few active components and a simple controller and produces
relatively low noise, choosing the inductor configuration can sometimes be a challenge. This article
discusses the impact of using coupled and uncoupled inductor windings in a SEPIC design.
I Q : What it is, what it isn’t, and how to use it . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
A device’s quiescent current (I Q ) is an important parameter for energy-efficient designs using low-
power DC/DC converters. This article explains how I Q can be only a portion of the system’s standby
power drain and the importance of looking for all possible input-current paths. Measurement techniques
are also covered to help designers avoid common measurement errors.
Backlighting the tablet PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Backlighting is one of the most power-hungry components of a tablet PC. This article gives guidance on
how to select the optimal WLED driver and LED-string configuration to meet system requirements
without sacrificing efficiency and therefore battery life. Included are efficiency comparisons for several
LED configurations.
Challenges of designing high-frequency, high-input-voltage DC/DC converters . . . .28
A DC/DC converter designed to operate at 1 or 2 MHz can reduce board space, but the higher frequency
impacts the power-supply system in more ways than just its size and efficiency. This article presents
several design examples that demonstrate the benefits and challenges of switching at higher
frequencies.
Index of Articles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
TI Worldwide Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
To view past issues of the
Analog Applications Journal , visit the Web site
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Analog Applications Journal
2Q 2011
High-Performance Analog Products
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Texas Instruments Incorporated
Introduction
Analog Applications Journal is a collection of analog application articles
designed to give readers a basic understanding of TI products and to provide
simple but practical examples for typical applications. Written not only for
design engineers but also for engineering managers, technicians, system
designers and marketing and sales personnel, the book emphasizes general
application concepts over lengthy mathematical analyses.
These applications are not intended as “how-to” instructions for specific
circuits but as examples of how devices could be used to solve specific design
requirements. Readers will find tutorial information as well as practical
engineering solutions on components from the following categories:
• Data Acquisition
• Power Management
• Interface (Data Transmission)
• Amplifiers: Audio
• Amplifiers: Op Amps
• Low-Power RF
• General Interest
Where applicable, readers will also find software routines and program
structures. Finally, Analog Applications Journal includes helpful hints and
rules of thumb to guide readers in preparing for their design.
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High-Performance Analog Products
2Q 2011
Analog Applications Journal
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Texas Instruments Incorporated
Data Acquisition
The IBIS model, Part 3: Using IBIS models
to investigate signal-integrity issues
By Bonnie C. Baker
Senior Applications Engineer
This article is the third of a three-part series on using a
digital input/output buffer information specification (IBIS)
simulation model during the development phase of a
printed circuit board (PCB). Part 1 discussed the funda-
mental elements of IBIS simulation models and how they
are generated in the SPICE environment. 1 Part 2 discussed
IBIS model validation. 2 The IBIS model brings a simple
solution to many of the signal-integrity problems that may
be encountered during the design phase. This article,
Part 3, shows how to use an IBIS model to extract impor-
tant variables for signal-integrity calculations and PCB
design solutions. Please note that the extracted values are
an integral part of the IBIS model.
Signal-integrity problems
When looking at a digital signal at both ends of a transmis-
sion line, the designer may be surprised at the result of
driving the signal into a PCB trace. Over relatively long
distances, electric signals act more like traveling waves
than instantaneous, changing signals. A good analogy that
describes electric-wave behavior on a circuit board is waves
in a pool. A ripple travels smoothly across the pool because
one volume of water has the same “impedance” as the next.
However, the pool wall presents a very different impedance
and reflects the wave in the opposite direction. Electric
signals injected into a PCB trace experience the same
phenomena, reflecting in a similar manner when imped-
ances are mismatched. Figure 1 shows a PCB setup with
mismatched termination impedances. A microcontroller,
Figure 1. PCB setup with mismatched termination impedances
MSP430 TM
ADS8326
T1
+
+
+
+
Clock
Clock
T2
+
+
+
+
CS
CS
T3
Data
Data
t CVC
CS/SHDN
Power Down
Sample
Conversion
t SVCS
DCLOCK
t CSD
Use positive clock edge for data transfer
High Impedance
High Impedance
0
B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
D OUT
(MSB)
(LSB)
t CONV
t SMPL
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Analog Applications Journal
2Q 2011
High-Performance Analog Products
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