LP3872_16 Datasheet, PDF (15/28 Pages) Texas Instruments – 1.5-A Fast Ultra-Low-Dropout Linear Regulators

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LP3872, LP3875
SNVS227H – FEBRUARY 2003 – REVISED JANUARY 2015
The primary source of noise in low-dropout regulators is the internal reference. In CMOS regulators, noise has a
low frequency component and a high frequency component, which depend strongly on the silicon area and
quiescent current. 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). Using an optimized trade-off of ground pin current and die size, LP3872 and LP3875
achieves low noise performance and low quiescent current operation.
The total output noise specification for LP3872 and LP3875 is presented in Electrical Characteristics. The Output
noise density at different frequencies is represented by a curve under typical performance characteristics.
8.2.3 Application Curves
VOUT
100mV/DIV
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (502s/DIV)
C_IN = C_OUT = 10 µF, OSCON
Figure 15. Load Transient Response
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (502s/DIV)
C_IN = C_OUT = 100 µF, POSCAP
Figure 17. Load Transient Response
ILOAD
1A/DIV
TIME (502s/DIV)
C_IN = C_OUT = 100 µF, OSCON
Figure 16. Load Transient Response
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (502s/DIV)
C_IN = C_OUT = 10 µF, Tantalum
Figure 18. Load Transient Response
VOUT
100mV/DIV
C_IN = C_OUT = 100 µF, Tantalum
ILOAD
1A/DIV
TIME (502s/DIV)
Figure 19. Load Transient Response
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