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Application Notes

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  Low Noise Varactor Biasing with Switching Regulators: Vanquishing Villainous Vitiators Vis-Г -Vis Vital Varactors &mdash AN85
  PDF, 490 Kb, File published: Aug 1, 2000
  Telecommunication, satellite links and set-top boxes all require tuning a high frequency oscillation. The actual tuning element, a varactor diode, requires high voltage bias for operation. The high voltage bias must be free of noise to prevent unwanted oscillator outputs. This publication details a method for generating noise free high voltage from low voltage inputs using switching regulators. Spurious oscillator outputs are below -90dBc. Suggested circuit and layout information is included. Appendices cover varactor diode theory and performance verification techniques.
  Extract from the document

  Application Note 85
  August 2000
  Low Noise Varactor Biasing with Switching Regulators
  Vanquishing Villainous Vitiators Vis-Г -Vis Vital Varactors
  Jim Williams and David Beebe
  INTRODUCTION “hyperabrupt” devices. Response modification is possible,
  with compromises in performance, particularly with regard
  to linearity and sensitivity.2 Telecommunication, satellite links and set-top boxes all
  require tuning a high frequency oscillator. The actual
  tuning element is a varactor diode, a 2-terminal device that
  changes capacitance as a function of reverse bias voltage.1 The oscillator is part of a frequency synthesizing
  loop, as detailed in Figure 1. A phase locked loop (PLL)
  compares a divided down representation of the oscillator
  with a frequency reference. The PLL’s output is level
  shifted to provide the high voltage necessary to bias the
  varactor, which closes a feedback loop by voltage tuning
  the oscillator. This loop forces the voltage controlled
  oscillator (VCO) to operate at a frequency determined by
  the frequency reference and the divider’s division ratio. Note 1. Theoretical considerations of varactor diodes are treated in
  Appendix A, “Zetex Variable Capacitance Diodes,” guest written by Neil
  Chadderton of Zetex.
  Note 2. The reader is again referred to Appendix A for in-depth discussion
  of varactor diodes. …

Design Notes

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  SOT-23 Switching Regulator with Integrated 1A Switch Delivers High Current Outputs in a Small Footprint &mdash DN232
  PDF, 91 Kb, File published: Jun 1, 2001
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  advertisement SOT-23 Switching Regulator with Integrated 1A Switch Delivers
  High Current Outputs in a Small Footprint – Design Note 232
  Albert Wu 5V Local Supply
  Figure 1 shows a typical 3.3V to 5V boost converter
  using the LT1930. The circuit can provide an impressive output current of 480mA while occupying less
  than 0.3" by 0.35" of board area (less than 0.105 in2).
  The efficiency, shown in Figure 2, remains above 83%
  over a wide load current range of 60mA to 450mA,
  reaching 86% at 200mA. The maximum output voltage
  ripple of this circuit is 40mVP-P, which corresponds
  to less than 1% of the nominal 5V output. Figure 3 is
  an oscillograph of the transient response. The lower
  waveform depicts a load step from 200mA to 300mA,
  the middle waveform shows the inductor current and
  the upper waveform shows the output voltage. The
  output voltage remains within 1% of the nominal value
  during the transient steps and displays a nice damped
  response with little ringing.
  L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
  of Linear Technology Corporation. All other trademarks are the property of their
  respective owners. 06/00/232_conv L1
  5.6ОјH VIN
  3.3V …

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  Very Low Dropout (VLDO) Linear Regulators Supply Low Voltage Outputs &mdash DN292
  PDF, 106 Kb, File published: Aug 2, 2002
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  advertisement Very Low Dropout (VLDO) Linear Regulators Supply
  Low Voltage Outputs
  Design Note 292
  Tom Gross
  Introduction
  With each new generation of computing systems, total
  power continues to increase while system voltages
  fall. CPU core voltages and logic supplies below 1.8V
  are now commonplace. Power supplies must not only
  regulate low output voltages but they must also operate
  from low input voltages. A low voltage, low dropout
  linear regulator is an attractive conversion option for
  applications where output currents are in the several
  ampere range. Component count and cost are low in
  comparison to switching regulator solutions, and with
  low input-to-output voltage differentials, efficiencies
  are comparable. MOSFET controller/driver are devices well suited to
  deliver lower output voltages from a supply of 1.8V
  or lower. Each device offers excellent line/load regulation, temperature performance and transient load
  step response.
  Figure 1 illustrates the LT1580 delivering 1.3V at 3A
  (maximum), from a 1.8V input supply. This particular
  conп¬Ѓguration requires a higher voltage supply to bias …

Articles

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  1.1A Boost Provides Soft-Start Capability in Tiny ThinSOT Package &mdash LT Journal
  PDF, 475 Kb, File published: Mar 25, 2005
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  DESIGN FEATURES 1.1A Boost Provides Soft-Start
  Capability in Tiny ThinSOT Package
  Introduction by Brian Adolf L1
  2.7ВµH
  C1
  4.7ВµF OFF ON C3
  0.047ВµF 4 D1 6 1 VIN SW SHDN
  LT3467
  5
  SS R1
  402k C4
  3.3pF VOUT
  5V
  765mA AT VIN = 4.2V,
  540mA AT VIN = 3.3V,
  360mA AT VIN = 2.6V 3 FB R2
  133k GND
  2 C2
  15ВµF C1, C2: X5R OR X7R, 6.3V
  D1: ON SEMICONDUCTOR MBRM120
  L1: SUMIDA CR43-2R7 95
  90
  VIN = 4.2V 85 …

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  SOT-23 Switching Regulators Deliver Low Noise Outputs in a Small Footprint &mdash LT Journal
  PDF, 125 Kb, File published: Feb 1, 1999
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  DESIGN FEATURES SOT-23 Switching Regulators Deliver
  Low Noise Outputs in a Small Footprint
  by Steve Pietkiewicz
  Introduction L1
  4.7ВµH 100 90
  EFFICIENCY (%) As portable electronics designers continue to press for reduction in
  component sizes, Linear Technology
  introduces the LT1611 and LT1613
  SOT-23 switching regulators. These
  current mode, constant frequency
  devices contain internal 36V switches
  capable of generating output power
  in the range of 400mW to 2W, in a 5lead SOT-23 package. The LT1613
  has a standard positive feedback pin
  and is designed to regulate positive
  voltages. The LT1611 has a novel
  feedback scheme designed to directly
  regulate negative output voltages
  without the use of level-shifting circuitry. Boost, single-ended primary
  inductance converters (SEPIC) and
  inverting configurations are possible
  with the LT1613 and LT1611. The
  high voltage switch allows hard-todo, yet popular DC/DC converter …

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  Micropower 5-Lead SOT-23 Switching Regulators Extend Battery Life in Space-Sensitive Applications &mdash LT Journal
  PDF, 238 Kb, File published: Sep 1, 1999
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  DESIGN FEATURES Micropower 5-Lead SOT-23
  Switching Regulators Extend Battery
  Life in Space-Sensitive Applications
  by Bryan Legates
  Introduction L1
  4.7ВµH VIN
  1.5V TO 3V The LT1615 and LT1617 are pin
  compatible with two other members
  of the PowerSOTв„ў family, the LT1613
  and LT1611, respectively. This allows
  the same board layout to be used to
  evaluate the performance of multiple
  devices. The LT1613 and LT1611 are
  both current mode, constant frequency devices, capable of producing
  larger output currents than the
  LT1615 and LT1617.1 LT1615 2-Cell to 3.3V
  Boost Converter
  A popular supply for many portable
  electronic devices, a 2-cell alkaline to
  3.3V converter with the LT1615 can
  deliver 60mA of load current. The
  circuit is shown in Figure 1 and the
  system efficiency appears in Figure 2. …

Model Line

Manufacturer's Classification

• Power Management > Switching Regulator > LCD/CCD/OLED Bias | SEPIC Regulators
• Power Management > Switching Regulator > Step-Up (Boost) Regulators > Internal Power Switch Boost