100mV/DIV

1A/DIV

TIME (502s/DIV)

100mV/DIV

1A/DIV

TIME (502s/DIV)

LP3852, LP3855

www.ti.com

SNVS174I – FEBRUARY 2003 – REVISED FEBRUARY 2015

10.2.2.5 Turnon Characteristics For Output Voltages Programmed to 2 V or Below

voltage (typically about 2.2 V). For output voltages programmed to 2 V or below, the regulator output may

momentarily exceed its programmed output voltage during start up. Outputs programmed to voltages above 2 V

are not affected by this behavior.

10.2.2.6 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

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, LP3852 and LP3855

achieve low noise performance and low quiescent-current operation.

The total output noise specification for LP3852 and LP3855 is presented in the Electrical Characteristics table.

The Output noise density at different frequencies is represented by a curve under Typical Characteristics.

10.2.3 Application Curves

Figure 22. Load Transient Response

Figure 23. Load Transient Response

11 Power Supply Recommendations

The LP3852 and LP3855 devices are designed to operate from an input voltage supply range between 2.5 V and

7 V. The input voltage range provides adequate headroom in order for the device to have a regulated output.

This input supply must be well regulated. An input capacitor of at least 10

μF is required.

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