LP38691DTX-1.8 NSC [National Semiconductor], LP38691DTX-1.8 Datasheet - Page 13

• Manufacturer Part Number: LP38691DTX-1.8
• Description: 500mA Low Dropout CMOS Linear Regulators Stable with Ceramic Output Capacitors
• Manufacturer: NSC [National Semiconductor]

Application Hints
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.
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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 in-
creases the total supply current (ground pin current).
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