LP2975 Datasheet, PDF (11/37 Pages) National Semiconductor (TI) – MOSFET LDO Driver/Controller

LP2975
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Performance Data
SNVS006F – SEPTEMBER 1997 – REVISED APRIL 2013
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 V_IN until the output voltage drops below the nominal value
(the nominal value is the output voltage measured with V_IN = 5V). I_L = 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. V_IN = 3.5V for this test.
0 ≤ I_L ≤ 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. I_L = 0.5A for this test.
3.5V ≤ V_IN ≤ 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. V_IN = 5V and I_L = 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. V_IN = 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 C_OUT
It is often desirable to decrease the value of C_OUT to save cost and reduce size. The design guidelines suggest
selecting C_OUT 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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