Datasheet Linear Technology LTC1709-85

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  Active Voltage Positioning Reduces Output Capacitors &mdash Design Solutions 10
  PDF, 130 Kb, File published: Nov 1, 1999
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  Design Solutions 10
  November 1999
  Active Voltage Positioning Reduces Output Capacitors
  by Robert Sheehan
  INTRODUCTION
  Power supply performance, especially transient response,
  is key to meeting today’s demands for low voltage, high
  current microprocessor power. In an effort to minimize
  the voltage deviation during a load step, a technique that
  has recently been coined “active voltage positioning” is
  generating substantial interest and gaining popularity in
  the portable computer market. The benefits include lower
  peak-to-peak output voltage deviation for a given load
  step, without having to increase the output filter capacitance. Alternatively, the output filter capacitance can be
  reduced while maintaining the same peak-to-peak transient response.
  BASIC PRINCIPLE
  The term “active voltage positioning” (AVP) refers to
  setting the power supply output voltage at a point that is
  dependent on the load current. At minimum load, the
  output voltage is set to a slightly higher than nominal level.
  At full load, the output voltage is set to a slightly lower than
  nominal level. Effectively, the DC load regulation is
  degraded, but the load transient voltage deviation will be …

Articles

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  LTC1709-85 High Efficiency Converter with VRM 8.5 Compliant VID Control Minimizes Input and Output Capacitors &mdash LT Journal
  PDF, 168 Kb, File published: Sep 1, 2001
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  DESIGN IDEAS LTC1709-85 High Efficiency Converter
  with VRM 8.5 Compliant VID Control
  Minimizes Input and Output Capacitors
  by Peter Guan
  Introduction Design Example
  high power-conversion efficiency for
  low voltage, high current applications.
  Because of the resulting output ripple
  current cancellation, lower value
  inductors can be used, resulting in a
  faster load transient response. This,
  plus the 5-bit VID table, makes this
  device particularly attractive for CPU
  power supply applications. The VID
  table complies with the Intel VRM 8.5
  specification. The LTC1709-85 is a 5-bit VID programmable, 2-phase, current mode,
  step-down switching regulator controller that drives two synchronous
  stages, composed of all N-channel
  power MOSFETs, 180В° out of phase.
  This architecture reduces the number of input and output capacitors
  without increasing the switching frequency. The relatively low switching
  frequency and integrated high current MOSFET drivers help provide Figure 1 shows the schematic diagram of a 30A power supply for the
  Intel PentiumВ® III microprocessor; its …

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Manufacturer's Classification

• Power Management > Switching Regulator > Digitally Programmable Regulators