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Texas Instruments Incorporated
High-Performance Analog Products
Analog Applications
Journal
Fourth Quarter, 2006
© Copyright 2006 Texas Instruments
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Texas Instruments Incorporated
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Analog Applications Journal
High-Performance Analog Products
4Q 2006
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Texas Instruments Incorporated
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Data Acquisition
Clamp function of high-speed ADC THS1041 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
The THS1041 clamp function enables it to generate and output a buffered dc voltage for a variety of
ADC applications. This article presents test data related to dc stability when the clamp function and SE
input configuration are applied at the same time. Included is an evaluation of how to obtain the best ac
performance and maximum input range with the THS1041 when using the clamp function.
Power Management
A 3-A, 1.2-V OUT linear regulator with 80% efficiency and P LOST < 1 W . . . . . . . . . . . . . 10
Using linear regulators for higher-current, low-output voltage applications has been a challenge for
many years. The dual-input rail, low dropout voltage, controllable soft starting, tracking, and integrated
PG features of the TPS74x01 family have made linear regulators more appealing. An evaluation of
stability, transient response, soft starting and sequencing is included in this article.
bq25012 single-chip, Li-ion charger and dc/dc converter for Bluetooth ® headsets . 13
A typical Bluetooth headset needs a rechargeable battery, a battery charger, and a 1.8-V dc/dc converter
to power the core chip. This article describes the capabilities of the bq25012, which has a fully
integrated 500-mA, single-cell Li-ion battery charger with a high-efficiency, 1-MHz, synchronous
switching step-down dc/dc converter.
Fully integrated TPS6300x buck-boost converter extends Li-ion battery life. . . . . . . . 15
A standard buck or boost converter has limitations when a 3.3-V output is required from a single-cell
Li-ion source. This article describes how the TPS6300x family excels in low-voltage portable
applications when efficiency, cost, and small size are important.
Interface (Data Transmission)
Detection of RS-485 signal loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Fault isolation and safety shutdown protocols are critical in many applications. This article shows
how a differential window comparator can be constructed with the passive-failsafe feature of two
SN65HVD3088E RS-485 transceivers and an AND gate.
Index of Articles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
TI Worldwide Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
To view past issues of the
Analog Applications Journal, visit the Web site
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Analog Applications Journal
4Q 2006
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)
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
4Q 2006
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Texas Instruments Incorporated
Data Acquisition
Clamp function of high-speed ADC THS1041
By Hui-Qing Liu (Email: liu_hui-qing@ti.com)
Applications Engineer, High-Speed ADC
Introduction
The THS1041 from Texas Instruments (TI) is a 10-bit,
40-MSPS, CMOS high-speed analog-to-digital converter
(ADC). It has many good features, including a single 3-V
supply, low power, a flexible input configuration, a built-in
programmable gain amplifier (PGA), and a built-in clamp
function. Because of these features, especially the built-in
clamp function, the THS1041 has been used in various
applications for many years. The clamp function enables
the device to generate and output a buffered dc voltage
for flexible ADC applications—for example, to provide a
common-mode voltage for the ADC or to allow dc restora-
tion on an ac-coupled video signal at the ADC analog input.
This function can be enabled or disabled. As shown in
Figure 1, the THS1041 clamp function consists of an on-chip
digital-to-analog converter (DAC), logic control, a clamp
input, a buffer, and a clamp output. The clamp output can
be a continuous or interrupted dc signal depending on
whether its Clamp pin receives a dc or pulse signal from an
external source. When this interrupted dc signal is applied
to the ADC single-ended (SE) input circuit to provide
common-mode voltage, the dc stability at the ADC analog
input becomes a concern. Some users have questioned dc
stability when the clamp function and SE input configura-
tion are applied at the same time. This article presents
some test data that explains how the dc voltage behaves in
this kind of application condition and how to get the best
ADC performance when the clamp function is on.
Clamp function
Figure 1 shows that the THS1041 clamp function is imple-
mented by setting four pins—Clampin, Clampout, Clamp,
and Mode—as well as the device internal registers. With
on-chip DAC, digital data from the THS1041 internal regis-
ter written by data bus b0 to b9 can be converted into an
analog dc voltage. This dc voltage is then buffered and
output to Clampout through internal switches. The internal
switch between the buffer and DAC can be on or off
depending on how the register is set. The DAC can provide
different dc voltages with a range between reference volt-
ages REFT and REFB for different application needs.
Setting different voltage levels at the Mode pin permits
the input of the internal buffer to also simply be connected
to an internal fixed dc voltage or to Clampin for an external
dc voltage input. The Clampout pin can be connected to
or disconnected from the buffer output of the clamp func-
tion by controlling either the dc or the pulse signal on the
Clamp pin. The THS1041 clamp function can be on with
an ADC differential input or SE input configuration. Its
output from Clampout can be connected to both analog
inputs, AIN+ and AIN–, to provide common-mode voltage,
or to only one of them for other applications.
Figure 1. THS1041 clamp function block diagram
WR
Logic
Control
I/O Bits
0to9
Clampin
Clampout
Buffer
DAC
Switch
Control
Switch
Control
Clamp
Mode
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Analog Applications Journal
4Q 2006
High-Performance Analog Products
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