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Application Notes

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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 …

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Manufacturer's Classification

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