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  Performance Verification of Low Noise, Low Dropout Regulators &mdash AN83
  PDF, 542 Kb, Datei veröffentlicht: 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 …

Konstruktionshinweise

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  Lowest Noise SOT-23 LDOs Have 20ВµA Quiescent Current, 20ВµVrms Noise &mdash DN220
  PDF, 114 Kb, Datei veröffentlicht: 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 …

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• Power Management > LDO Linear Regulators > Positive Linear Regulators (LDO)