LP38691_15 Datasheet, PDF (18/34 Pages) Texas Instruments – LP3869x/-Q1 500-mA Low-Dropout CMOS Linear Regulators Stable With Ceramic Output Capacitors

LP38691, LP38693, LP38691-Q1, LP38693-Q1
SNVS321O – JANUARY 2005 – REVISED DECEMBER 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 paid to the units of measurement. Spot noise is measured in units µV√Hz or nV√Hz, and total output
noise is measured in µV_RMS.
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 decreases 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
Figure 28. V_OUT vs V_EN, ON (LP38693 Only)
Figure 29. V_OUT vs V_EN, OFF (LP38693 Only)
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