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  60V, High Efficiency Buck Switching Regulators in SO-8 &mdash DN202
  PDF, 104 Kb, 档案已发布: Apr 1, 1999
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  advertisement 60V, High Efficiency Buck Switching Regulators in SO-8
  Design Note 202
  Ajmal Godil
  The LT®1676/LT1776 are wide input range, high efficiency buck (step-down) switching regulators in SO-8
  packages. Typical applications include automotive
  DC/DC conversion, telecom 48V step-down and
  IEEE1394 (FireWire) step-down converters. Since both parts allow such a wide input voltage range,
  they use two techniques to optimize efficiency. First,
  the internal control circuitry draws power from the VCC
  pin, which is normally connected to the output supply.
  During start-up, the controllers draw power from VIN.
  When the output voltage exceeds 2.9V, the bias power
  comes from the output. This reduces quiescent power
  consumption by hundreds of milliwatts when operating at high input voltage. Second, the switch circuitry
  maintains a fast rise time at high loads (see Figure 2).
  Both of these factors help in maximizing efficiency with
  high input voltages. At light loads, the switch rise time
  slows down (see Figure 3) to avoid pulse skipping, thus
  maintaining a constant frequency from heavy to light
  loads. This helps significantly in reducing the output Both the LT1676 and the LT1776 can accept input
  voltages from 7V to 60V. The LT1676 has a nominal
  switching frequency of 100kHz whereas the LT1776
  runs at 200kHz. For higher input voltage applications, …

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  LT1777 High Voltage, Low Noise Buck Switching Regulator &mdash DN212
  PDF, 115 Kb, 档案已发布: Sep 2, 1999
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  advertisement LT1777 High Voltage, Low Noise Buck Switching Regulator
  Design Note 212
  Ajmal Godil
  The LTВ®1777 is a wide input range buck (step-down)
  switching regulator specially designed for low noise applications. The LT1777 can be beneficial in applications
  where low noise is critical, such as telecom, automotive
  cellular and GPS receiver power supplies. The schematic
  in Figure 1 highlights the capabilities of the LT1777. VSW NODE
  VOLTAGE
  10V/DIV SWITCH
  CURRENT
  200mA/DIV The LT1777 can accept input voltages from 7.4V to 48V
  and has a nominal switching frequency of 100kHz. The
  monolithic die includes an onboard 700mA peak current
  switch, oscillator, control and protection circuitry. It uses
  current mode control that delivers excellent dynamic
  input supply rejection and short-circuit protection. In
  order to achieve low noise, the LT1777 is equipped with
  dI/dt limiting circuitry that is programmed via a small
  inductor (LSENSE in Figure 1) in the power path. It also
  contains internal circuitry to limit dV/dt during switch
  turn-on and turn-off.
  Figure 2 shows the VSW node voltage and switch current …

文章

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  Generating Low Cost, Low Noise, Dual-Voltage Supplies &mdash LT Journal
  PDF, 72 Kb, 档案已发布: Feb 1, 1999
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  DESIGN IDEAS Generating Low Cost, Low Noise,
  Dual-Voltage Supplies
  by Ajmal Godil
  Some sensitive electronic applications, such as telecommunication and
  data acquisition, require both 5V and
  –5V low noise supplies, which may
  have to be generated from a single
  high voltage positive supply. The circuit in Figure 1 shows a cost-effective
  way to generate 5V and –5V from a
  single 10V–28V supply by using the
  low noise LT1777 and a few off-theshelf components.
  The LT1777 is a step-down regulator specially designed for low noise
  applications. In order to achieve low
  VIN
  10V–28V
  4
  10
  3 SHDN 14
  100pF VCC VSW VIN VD SHDN
  VC FB
  LT1777 GND
  GND 12
  R3 …

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  Wide Input Range, High Efficiency Step-Down Switching Regulators &mdash LT Journal
  PDF, 257 Kb, 档案已发布: Nov 1, 1998
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  DESIGN FEATURES Wide Input Range, High Efficiency
  Step-Down Switching Regulators
  by Jeff Schenkel
  Introduction
  The LT1676 and LT1776 are Linear
  Technology’s latest offerings for high
  efficiency step-down switching regulator applications. These two parts
  are pin-for-pin compatible and virtually identical in operation, the only
  difference being their internal oscillator frequencies—100kHz for the
  LT1676 vs 200kHz for the LT1776.
  They operate in a fixed frequency
  mode (as opposed to constant offtime or on-time, for instance) and can
  be externally synchronized to a higher
  switching frequency.
  The internal output switch is rated
  at a nominal peak current of 700mA,
  which typically accommodates DC
  output currents of up to 500mA. The
  input voltage range is 7.4V to 60V.
  Maintaining acceptable efficiency in
  the upper half of this input voltage
  range requires very fast output-switch
  edge rates. The LT1676/LT1776 contain specialized output circuitry to …

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• Power Management > Switching Regulator > Step-Down (Buck) Regulators > Internal Power Switch Buck | High Input Voltage Buck