Datasheet

LP38691-ADJ, LP38693-ADJ
SNVS324I –JANUARY 2005–REVISED APRIL 2013 www.ti.com
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 1Hz 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/root-Hz or nV/root-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 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 (ground pin current).
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