LP38691, LP38693, LP38691-Q1, LP38693-Q1

SNVS321N – JANUARY 2005 – REVISED MARCH 2015

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9.2.2.8 Output Noise

Noise is specified in two ways: Spot Noise or Output Noise Density is the RMS sum of all noise sources,

measured at the regulator output, at a specific frequency (measured with a 1-Hz bandwidth). This type of noise is

usually plotted on a curve as a function of frequency. Total Output Noise or Broad-Band Noise is the RMS sum

of spot noise over a specified bandwidth, usually several decades of frequencies.

Attention should be paid to the units of measurement. Spot noise is measured in units µV

√Hz or nV√Hz, and total

The primary source of noise in low-dropout regulators is the internal reference. Noise can be reduced in two

ways: by increasing the transistor area or by increasing the current drawn by the internal reference. Increasing

the area will decrease the chance of fitting the die into a smaller package. Increasing the current drawn by the

internal reference increases the total supply current (GND pin current).

9.2.3 Application Curves

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