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Application Notes

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  Minimizing Switching Regulator Residue in Linear Regulator Outputs &mdash AN101
  PDF, 358 Kb, Language: en, File published: Jul 16, 2005, Pages: 12
  Application Note 101. Linear regulators are commonly employed to post-regulate switching regulator outputs. Benefits include improved stability, accuracy, transient response and lowered output impedance. Ideally, these performance gains would be accompanied by markedly reduced switching regulator generated ripple and spikes. In practice, all linear regulators encounter some difficulty with ripple and spikes, particularly as frequency rises. This publication explains the causes of linear regulators' dynamic limitations and presents board level techniques for improving ripple and spike rejection. A hardware based ripple/spike simulator is presented, enabling rapid breadboard testing under various conditions. Three appendices review ferrite beads, inductor based filters and probing practice for wideband, sub-millivolt signals.
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  Application Note 101
  July 2005
  Minimizing Switching Regulator Residue
  in Linear Regulator Outputs
  Banishing Those Accursed Spikes
  Jim Williams
  INTRODUCTION
  Linear regulators are commonly employed to post-regulate
  switching regulator outputs. Benefits include improved
  stability, accuracy, transient response and lowered output
  impedance. Ideally, these performance gains would be
  accompanied by markedly reduced switching regulator
  generated ripple and spikes. In practice, all linear regulators
  encounter some difficulty with ripple and spikes, particularly as frequency rises. This effect is magnified at small
  regulator VIN to VOUT differential voltages; unfortunate,
  because such small differentials are desirable to maintain
  efficiency. Figure 1 shows a conceptual linear regulator
  and associated components driven from a switching
  regulator output.
  The input filter capacitor is intended to smooth the ripple and
  spikes before they reach the regulator. The output capacitor maintains low output impedance at higher frequencies,
  improves load transient response and supplies frequency
  compensation for some regulators. Ancillary purposes include noise reduction and minimization of residual inputderived artifacts appearing at the regulators output. It is …

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  Performance Verification of Low Noise, Low Dropout Regulators &mdash AN83
  PDF, 542 Kb, File published: Mar 1, 2000
  In an increasing trend, telecommunications, networking, audio and instrumentation require low noise power supplies. In particular, there is interest in low noise, low dropout linear regulators (LDO). Establishing and specifying LDO dropout performance is relatively easy to do. Verifying that a regulator meets dropout specification is similarly straightforward. Accomplishing the same missions for noise and noise testing is considerably more involved. The noise bandwidth of interest must be called out, along with operating conditions. Low noise performance is affected by numerous subtleties; changes in operating conditions can cause unwelcome surprises. Because of this, LDO noise must be quoted under specified operating and bandwidth conditions to be meaningful. Failure to observe this precaution results in misleading data and erroneous conclusions. This Application Note suggests a noise testing method, details its implementation and presents results.
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  Application Note 83
  March 2000
  Performance Verification of Low Noise,
  Low Dropout Regulators
  Silence of the Amps
  Jim Williams and Todd Owen, Linear Technology Corporation
  Introduction
  In an increasing trend, telecommunications, networking,
  audio and instrumentation require low noise power supplies. In particular, there is interest in low noise, low
  dropout linear regulators (LDO). These components power
  noise-sensitive circuitry, circuitry that contains noisesensitive elements or both. Additionally, to conserve power,
  particularly in battery driven apparatus such as cellular
  telephones, the regulators must operate with low input-tooutput voltages.1 Devices presently becoming available
  meet these requirements (see separate section, “A Family
  of 20µVRMS Noise, Low Dropout Regulators”).
  Noise and Noise Testing
  Establishing and specifying LDO dropout performance is
  relatively easy to do. Verifying that a regulator meets
  dropout specification is similarly straightforward. Accomplishing the same missions for noise and noise testing is
  considerably more involved. The noise bandwidth of interest must be called out, along with operating conditions.
  Operating conditions can include regulator input and
  output voltage, load, assorted discrete components, etc.
  Low noise performance is effected by numerous subtleties; changes in operating conditions can cause unwelcome surprises.2 Because of this, LDO noise must be …

Design Notes

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  Lowest Noise SOT-23 LDOs Have 20ВµA Quiescent Current, 20ВµVrms Noise &mdash DN220
  PDF, 114 Kb, File published: Dec 1, 1999
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  advertisement Lowest Noise SOT-23 LDOs Have 20ВµA Quiescent Current,
  20µVRMS Noise – Design Note 220
  Todd Owen and Jim Williams Applying the Regulators
  Applying the regulators is simple. Figure 1 shows a
  minimum parts count, 3.3V output design. This circuit
  appears similar to conventional approaches with a 1ОјF OUT
  0.01ОјF LT1761-3.3
  SHDN 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.
  500
  450 3.3V/100mA
  20ОјVRMS
  NOISE (TYP) VIN > 3.7V IN notable exception: a bypass pin (BYP) is returned to
  the output via a 0.01ОјF capacitor. This path п¬Ѓlters the
  internal reference’s output, minimizing regulator output
  noise. It is the key to the 20ОјVRMS noise performance.
  A shutdown pin (SHDN), when pulled low, turns off the
  regulator output while keeping current drain inside 1ОјA.
  Dropout characteristics appear in Figure 2. Dropout
  scales with output current, falling to less than 100mV
  at low currents. DROPOUT VOLTAGE (mV) Telecom and instrumentation applications often require
  a low noise voltage regulator. Frequently this requirement coincides with the need for low regulator dropout …

Articles

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  Dual Regulators Offer Flexibility with Independent Shutdown Control and Adjustable Start-Up Timing &mdash LT Journal
  PDF, 210 Kb, File published: May 1, 2004
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  DESIGN IDEAS Dual Regulators Offer Flexibility
  with Independent Shutdown Control
  and Adjustable Start-Up Timing
  by Todd Owen Introduction DESIGN IDEAS
  Dual Regulators Offer Flexibility
  with Independent Shutdown Control
  and Adjustable Start-Up Timing . 29
  Todd Owen 4A, 4MHz Monolithic Synchronous
  Regulator with Tracking
  offers a Compact Solution
  for Power Supply Sequencing . 31
  Joey M. Esteves Synchronous Boost Converter
  with Output Disconnect
  Delivers 4W from Two Cells . 32
  Dongyan Zhou Boost Converter
  Drives 1A White LEDs . 33
  Keith Szolusha Smart Card
  Interfaces Made Easy . 34
  Steven Martin LCD Power Supply
  Provides В±15V Plus LED Driver. 35
  Mike Shriver Linear Technology Magazine May 2004 VIN
  3.7V TO 20V IN OUT1
  0.01ВµF 1ВµF BYP1 10ВµF 3.3V …

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Manufacturer's Classification

• Power Management > LDO Linear Regulators > Positive Linear Regulators (LDO) | Extended Temperature (H & MP) Linear Regulators