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Minimizing Switching Regulator Residue in Linear Regulator Outputs (Application Note 101)

Learn how to reduce switching regulator ripple and high-frequency spikes in linear regulator outputs using filter capacitors, ferrite beads, and proper measurement techniques.

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Overview

This application note, authored by Jim Williams, explores techniques for minimizing switching regulator-generated ripple and high-frequency spikes in linear regulator outputs. It details why linear regulators struggle to reject wideband spikes due to limited gain-bandwidth and parasitic effects in passive components. The document introduces a ripple/spike simulator circuit for evaluating regulator performance and discusses mitigation strategies, such as using ferrite beads, optimizing capacitor selection, and managing layout parasitics to achieve low-noise DC outputs for sensitive applications.

Use Cases

  • Post-regulation for switching power supplies
  • Noise-sensitive video and communication circuitry
  • Power supply filtering and decoupling
  • Evaluating linear regulator high-frequency rejection
  • Designing low-noise power distribution networks

Topics

linear regulator
switching regulator
ripple rejection
high frequency spikes
PSRR
LT1763
parasitic inductance
ferrite beads
noise reduction
post-regulation

Referenced Parts

2518065007Y6

Fair-Rite

surface mounted ferrite bead (Fair-Rite 2518065007Y6).

74AHC04

Generic

74AHCO4 SPIKE GATING/BUFFER

HP-10240B

Hewlett-Packard

COUPLING CAPACITOR HP-10240B

2743002122

Fair-Rite

FB = FERRITE BEAD. FAIR-RITE 2743002122.

LT1006

Linear Technology

A2 LT1006

LT1210

Linear Technology

A1 LT1210

LT1460

Linear Technology

LT1460 2.5V

LT1712

Linear Technology

C2, 1/2 LT1712 C1, 1/2 LT1712

LT1763

Linear Technology

Figure 3 shows rejection performance for an LT1763 low dropout linear regulator.

HP-11048C

Hewlett-Packard

50Ω TERMINATOR HP-11048C