LP2975 Datasheet, PDF (7/19 Pages) National Semiconductor (TI) – MOSFET LDO Driver/Controller

Typical Performance Characteristics Unless otherwise specified: T_A = 25˚C, C_IN = 1 µF, ON/OFF pin
is tied to 1.5V. (Continued)
Controller Gain and Phase Response
DS100034-36
Reference Designs
The LP2975 controller can be used with virtually any
P-channel MOSFET to build a wide variety of linear voltage
regulators.
Since it would be impossible to document all the different
voltage and current combinations that could be built, a num-
ber of reference designs will be presented along with perfor-
mance data for each.
THE PERFORMANCE DATA SHOWN IS ACTUAL TEST
DATA, BUT IS NOT GUARANTEED.
DESIGN #1: V_OUT = 5V @ 5A (Refer to Typical Application
Circuits)
COMPONENTS:
C_IN = 82 µF Aluminum Electrolytic
C_OUT = 120 µF Aluminum Electrolytic
C_F = 220 pF
R_SC = 10 mΩ
P-FET = NDP6020P
Heatsink: (assuming V_IN ≤ 7V and T_A ≤ 60˚C) if protection
against a continuous short-circuit is required, a heatsink with
θ_S-A ≤ 1.5 ˚C/W must be used. However, if continuous short-
circuit survivability is not needed, a heatsink with θ_S-A ≤
6 ˚C/W is adequate.
PERFORMANCE DATA:
Dropout Voltage
Dropout voltage is defined as the minumum input-to-output
differential voltage required by the regulator to keep the out-
put in regulation. It is measured by reducing V_IN until the out-
put voltage drops below the nominal value (the nominal
value is the output voltage measured with V_IN = 5.5V). I_L =
5A for this test.
DROPOUT VOLTAGE = 323 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 ex-
pressed as a percentage. V_IN = 5.6V for this test.
5 mA ≤ I_L ≤ 5A: LOAD REGULATION = 0.012%
0 ≤ I_L ≤ 5A: LOAD REGULATION = 0.135%
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 ex-
pressed as a percentage. I_L = 5A for this test.
5.4V ≤ V_IN ≤ 10V: LINE REGULATION = 0.03%
Output Noise Voltage
Output noise voltage was measured by connecting a wide-
band AC voltmeter (HP 400E) directly across the output ca-
pacitor. V_IN = 6V and I_L = 5A for this test.
NOISE = 75 µV (rms)
Transient Response
Transient response is defined as the change in output volt-
age which occurs after the load current is suddenly changed.
V_IN = 5.6V for this test.
The load resistor is connected to the regulator output using a
switch so that the load current increases from 0 to 5A
abruptly. The change in output voltage is shown in the scope
photo below (the vertical scale is 200 mV/division and the
horizontal scale is 10 µs/division). The regulator nominal out-
put (5V) is located on the center line of the photo.
The output shows a maximum change of about −600 mV
compared to nominal. This is due to the relatively small out-
put capacitor chosen for this design. Increasing C_OUT greatly
improves transient response (see Designs #2 and #3).
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