LP2975 datasheet(11/37 Pages) TI1

11 / 37 page

LP2975

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SNVS006F – SEPTEMBER 1997 – REVISED APRIL 2013

Performance Data

Dropout Voltage

Dropout voltage is defined as the minimum input-to-output differential voltage required by the regulator to keep

the output in regulation. It is measured by reducing VIN until the output voltage drops below the nominal value

(the nominal value is the output voltage measured with VIN = 5V). IL = 0.5A for this test.

DROPOUT VOLTAGE = 141 mV

Load Regulation

Load regulation is defined as the maximum change in output voltage as the load current is varied. It is measured

by changing the load resistance and recording the minimum/maximum output voltage. The measured change in

output voltage is divided by the nominal output voltage and expressed as a percentage. VIN = 3.5V for this test.

≤ IL ≤ 0.5A: LOAD REGULATION = 0.034%

Line Regulation

Line regulation is defined as the maximum change in output voltage as the input voltage is varied. It is measured

by changing the input voltage and recording the minimum/maximum output voltage. The measured change in

output voltage is divided by the nominal output voltage and expressed as a percentage. IL = 0.5A for this test.

3.5V

≤ VIN ≤ 6V: LINE REGULATION = 0.017%

Output Noise Voltage

Output noise voltage was measured by connecting a wideband AC voltmeter (HP 400E) directly across the

output capacitor. VIN = 5V and IL = 0.5A for this test.

NOISE = 85 µV (rms)

Transient Response

Transient response is defined as the change in output voltage which occurs after the load current is suddenly

changed. VIN = 3.5V for this test.

The load resistor is connected to the regulator output using a switch so that the load current increases from 0 to

0.5A abruptly. The change in output voltage is shown in the scope photo (the vertical scale is 20 mV/division and

the horizontal scale is 50 µs/division). The regulator nominal output (3V) is located on the center line of the

photo. A maximum change of about

−50 mV is shown.

Figure 18. Transient Response for 0–0.5A Load Step

Minimizing COUT

It is often desirable to decrease the value of COUT to save cost and reduce size. The design guidelines suggest

selecting COUT to set the first pole ≤ 200 Hz (see later section, Output Capacitor), but this is not an absolute

requirement in all cases.

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