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Texas Instruments Incorporated
High-Performance Analog Products
Analog Applications
Journal
Second Quarter, 2007
© Copyright 2007 Texas Instruments
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Texas Instruments Incorporated
IMPORTANT NOTICE
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enhancements, improvements, and other changes to its products and services at any time and to discontinue
any product or service without notice. Customers should obtain the latest relevant information before placing
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TI warrants performance of its hardware products to the specifications applicable at the time of sale in
accordance with TI's standard warranty. Testing and other quality control techniques are used to the extent TI
deems necessary to support this warranty. Except where mandated by government requirements, testing of all
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TI assumes no liability for applications assistance or customer product design. Customers are responsible for
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Dallas, Texas 75265
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Analog Applications Journal
High-Performance Analog Products
2Q 2007
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Texas Instruments Incorporated
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Data Acquisition
Conversion latency in delta-sigma converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Conversion latency can be a problem when working with multiple small-signal, low-frequency sensors in
a system. This article compares cycle-latancy behavior of various delta-sigma converters and shows how
TI’s zero-latency ADCs are well suited for many multipliexed small-signal applications.
Power Management
Enhanced-safety, linear Li-ion battery charger with thermal regulation
and input overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Using unregulated power sources can easily drive linear Li-ion battery chargers beyond safe thermal
operating limits. The bq2406x chargers offer thermal regulation and input overvoltage protection that
alleviate thermal concerns while maximizing the charge rate and minimizing the charging time.
Current balancing in four-pair, high-power PoE applications . . . . . . . . . . . . . . . . . . . . 11
IEEE standards limit the power available to peripherals using two-pair architucture. This article
describes a current-balancing technique that uses four-pair architecture to achieve up to 50 watts of
input power to end equipment.
Interface (Data Transmission)
Enabling high-speed USB OTG functionality on TI DSPs . . . . . . . . . . . . . . . . . . . . . . . . 18
USB On-The-Go (OTG) enables connectivity to various USB devices without a PC host. This article
provides insight to getting the TUSB60xx OTG-capable devices to gluelessly provide a USB interface to
TI processors that supports the VLYNQ interface—such as the DaVinci™ family, the DM320, and the
OMAP™ family.
Amplifiers: Op Amps
New zero-drift amplifier has an I Q of 17 µA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Micropower applications require very small input offset, offset drift, and very low noise. This article
provides an indepth look at the OPA333—a low-noise, chopper-stabilized, micropower operational
amplifier which operates from a 1.8-V supply with very low quiescent current.
General Interest
Spreadsheet modeling tool helps analyze power- and ground-plane
voltage drops to keep core voltages within tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . 29
PCB power- and ground-plane voltage drops can become a real problem when working with very low
core voltages. This article shows how to use your spreadsheet software to model a PCB layout to predict
voltage drops for various copper thicknesses and temperatures. Using the spreadsheet surface-charting
function, a 3D map of the voltage drops can be generated for quick visual analysis.
Index of Articles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
TI Worldwide Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
To view past issues of the
Analog Applications Journal, visit the Web site
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Analog Applications Journal
2Q 2007
High-Performance Analog Products
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Introduction
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: Op Amps
• 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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Analog Applications Journal
High-Performance Analog Products
2Q 2007
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Texas Instruments Incorporated
Data Acquisition
Conversion latency in delta-sigma converters
By Bonnie C. Baker (Email: bonnie@ti.com)
Senior Applications Engineer
Small-signal sensors often generate slow-moving dc signals.
For these types of sensors, the delta-sigma (∆Σ) analog-to-
digital converter (ADC) eliminates most of the analog input
circuitry by providing a complete high-resolution, low-noise
solution. Some systems have multiple sensors generating
low-frequency signals. This situation may require a high-
resolution, low-noise ADC with a multiplexer at its input.
An example of a multiplexed sensor system is an auto-
motive diagnostic application where numerous small-signal
sensors monitor temperature, tire pressure, air-bag readi-
ness, etc. (see Figure 1). Examples of other sensor-input
multiplexed systems are found in industrial-control, medical,
avionics, and process-control applications. Even though the
sensors at the input of the multiplexer in these systems
present low-frequency (nearly dc) signals, switching from
channel to channel creates the need for an ADC that is
capable of a high-speed response.
There are two common units of measure that describe
the latency of an ADC: cycles and seconds. Cycle latency is
the number of complete data cycles between the conversion
initiation and the availability of the corresponding output
data. Latency time, measured in seconds, tells the user
how fast fully settled conversions can be performed.
In the system in Figure 1, the multiple-channel ADC
must have high resolution, low
noise, zero-cycle latency, and low
latency time. (Zero latency or
0-cycle latency is sometimes called
no latency.)
ADC cycle latency
For ADCs, cycle latency is the
number of complete data cycles
between the initiation of the input-
signal conversion and the availability
of the corresponding output data
(see Figure 2). The unit of measure
for this definition of latency is
N-cycle latency, where N is a whole
number. Figure 2 shows the timing
diagrams for a 0-cycle-latency (or
zero-latency) ADC and a 4-cycle-
latency ADC. In Figure 2(a), with
0-cycle latency, the sampling period
of N+0 is initiated. The output data
of N+0 is acquired before the sam-
pling period of N+1 is initiated. In
Figure 2(b), with 4-cycle latency,
the sampling period of N+0 is
Figure 1. Example multiplexed sensor system
Load
Cell
Pressure
Sensor
Multichannel
ADC
Digital
Output
Thermistor
10 m
Ω
Figure 2. Comparison of cycle-latency behavior of two
∆Σ
ADCs
Single-Cycle
Conversion
N+2
N+0
N+0
N+1
N+4
Analog IN
N+3
N+7
N+5
N+6
Data OUT
N–5
N+0
N+1
N+2
N+3
N+4
N+5
N+6
N+7
Data
Invalid
(a) 0-cycle-latency
∆Σ
ADC
N+2
N+0
N+1
N+4
Analog IN
N+3
N+7
N+5
N+6
Data OUT
N–5
N–4
N–3
N–2
N–1
N+0
N+1
N+2
N+3
Data
Invalid
∆Σ
(b) 4-cycle-latency
ADC
5
Analog Applications Journal
2Q 2007
High-Performance Analog Products
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