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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.
  Extract from the document

  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 …

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  Isolated RS485 Transceiver Breaks Ground Loops &mdash DN228
  PDF, 992 Kb, File published: Apr 2, 2001
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  Isolated RS485 Transceiver Breaks Ground Loops – Design Note 228
  Mitchell Lee Previously, isolation was achieved by using at least three
  optoisolators and a separate isolated power supply. The
  LTC1535 replaces not only the optoisolators, but also the
  power supply, as it includes an on-chip DC/DC converter.
  Other features include selectable driver slew rate to reduce
  EMI and susceptibility to reflections, full-duplex pinout
  and fail-safe detection of open and shorted lines.
  The LTC1535 consists of two separate dice assembled on
  a proprietary, isolated lead frame. The lead frame includes
  integral coupling capacitors that bridge the isolation barrier
  and exhibit 2,500VRMS guaranteed standoff. Data communication takes place via the coupling capacitors, while
  an on-chip, 400kHz push-pull converter sends power to the
  isolated side through a small transformer. Total common
  mode capacitance across the barrier amounts to less than
  20pF, with the transformer accounting for about 16pF of
  the total. Figure 1 shows the complete circuit for a fully
  isolated RS485 port.
  Internally, the two halves of the LTC1535 communicate
  in a ping-pong fashion, first sending transmit data to the
  isolated side and then sending receive data back to the
  nonisolated side. The sampling nature of the internal communications link means that some jitter is introduced into
  the data; this limits the useful baud rate to approximately …

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  Ultralow Noise Switching Power Supplies Simplify EMI Compliance &mdash DN316
  PDF, 94 Kb, File published: Jul 2, 2003
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  advertisement Ultralow Noise Switching Power Supplies Simplify
  EMI Compliance – Design Note 316
  David Canny
  Introduction
  Most electronic products must pass electromagnetic
  interference (EMI) compliance tests—such as the FCC
  Part 15 rules in the US—before they can be released
  into the market. When a company’s product fails EMI
  compliance tests, the company loses control of the
  development process, shipping dates begin to slip,
  projected revenues diminish and expenses start piling
  up. Furthermore, excessive noise can interfere with
  sensitive electronics within the product itself. So it is
  essential that electronic products are designed from
  the beginning with EMI attenuation in mind. Often the
  EMI compliance problem lies in the product’s switching power supply. In these cases, the best solution is
  prevention by using an ultralow noise switching power
  supply in the initial design, rather than adding shields
  and п¬Ѓlters to the product after the fact. Circuit Description
  Figure 1 shows the LTВ®3439, one of several low noise
  switchers available from Linear Technology. Ultralow
  noise and low EMI are achieved by controlling both
  the output switch voltage and current slew rates. This …

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  Tiny Versatile Buck Regulators Operate from 3.6V to 36V Input &mdash DN367
  PDF, 80 Kb, File published: May 10, 2005
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  advertisement Tiny Versatile Buck Regulators Operate from 3.6V to 36V Input
  Design Note 367
  Hua (Walker) Bai
  Introduction
  Linear Technology offers two new buck regulators that
  operate from a wide input voltage range (3.6V to 36V)
  and take so little space that they easily solve many difficult power supply problems. The LT®1936 and LT1933
  are perfect for applications with disparate power inputs
  or wide range input power supplies such as automotive
  batteries, 24V industrial supplies, 5V logic supplies
  and various wall adapters. Both parts are monolithic
  current mode PWM regulators which provide excellent
  line and load regulation and dynamic response. They
  operate at a 500kHz switching frequency, enabling the
  use of small, low cost inductors and ceramic capacitors,
  resulting in low, predictable output ripple.
  Small Size and Versatility
  The LT1936 regulator includes a 1.9A power switch in
  a tiny, thermally enhanced 8-lead MSOP. The LT1933
  regulator includes an internal 0.75A power switch in a
  tiny 6-lead ThinSOTв„ў package, which occupies less than
  0.15in2 board space. The LT1936 offers the option of
  external compensation for design flexibility or internal …

Articles

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  A Simple Solution to Low Noise, Isolated Power Conversion &mdash LT Journal
  PDF, 181 Kb, File published: Nov 1, 2002
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  DESIGN IDEAS A Simple Solution to Low Noise,
  Isolated Power Conversion by Tom Sheehan
  Introduction
  the turns ratio. Rectifiers on the secondary side generate the DC output
  voltage. The output capacitor is for
  hold up and filtering. If required, an
  additional inductor and capacitor can
  be added to reduce the output noise
  even further.
  Control of the voltage and current
  slew rate is maintained via two control loops. One loop controls the
  output switch dV/dt and the other
  loop controls the output switch dI/dt.
  Output slew control is achieved by
  comparing the two currents generated by these slewing events to a
  current set by the external resistor
  RSL.
  The frequency of the internal oscillator can be set from 20kHz to 250kHz
  with an external resistor and capacitor, RT and CT. Each output switch is
  driven at half the frequency of the
  oscillator. The SYNC pin can be used
  to synchronize the switching to an
  external clock. A SHDN pin can be …

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  Micropower LDO Has the Lowest Noise and Quiescent Current in SOT-23 &mdash LT Journal
  PDF, 312 Kb, File published: Jun 1, 1999
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  DESIGN FEATURES Micropower LDO Has the Lowest Noise
  and Quiescent Current in SOT-23
  by Todd Owen
  Introduction
  A cell phone rings, a pager beeps.
  Wireless communications devices are
  everywhere. These RF circuits have a
  myriad of power supply requirements.
  Most important in many applications
  is low noise operation, to prevent
  unwanted sidebands on RF amplifiers. Second is low power operation,
  which translates directly to extended
  operating time in battery-powered
  devices. In addition, portability
  requires small size, which makes
  small packages for regulators and
  stability with small surface mount
  ceramic capacitors a plus. Another
  factor that can weigh in is low voltage
  operation, both for the input and output. Satisfying all of these needs at
  once can be a difficult challenge. Table 1. Evaluation of available SOT-23 low noise, low dropout regulators Part
  Competitor 1
  (5V Output) …

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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