LP2975 datasheet(7/19 Pages) NSC

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Typical Performance Characteristics Unless otherwise specified: T

A = 25˚C, CIN = 1 µF, ON/OFF pin

is tied to 1.5V. (Continued)

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:

IN = 82 µF Aluminum Electrolytic

OUT = 120 µF Aluminum Electrolytic

F = 220 pF

SC =10mΩ

P-FET = NDP6020P

Heatsink: (assuming V

IN ≤ 7V and TA ≤ 60˚C) if protection

against a

continuous short-circuit is required, a heatsink with

S-A ≤ 1.5 ˚C/W must be used. However, if continuous short-

circuit survivability is not needed, a heatsink with

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). IL =

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.

5mA

≤ I

L ≤ 5A: LOAD REGULATION = 0.012%

≤ 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 IL = 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.

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).

Controller Gain and Phase Response

DS100034-36

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