EN

R3

51.1 k:

VIN = 5V

LP38501

C3

10 PF

VOUT

CV+

1 PF

& 10 PF

5V

+IN

-IN

RSENSE

58 m:

LMP8646

C1

10 PF

ADJ

0.6V

RG

51.7 k:

CG

10 nF

ROUT

50:

RFBT

19.1 k:

RFBB

6.04 k:

RLOAD

2 :

RG

V+

V-

IN

OUT

ENABLE

ILIMIT =

ICLOSE_LOOP = 1A

VCLOSE_LOOP = 2 V

-0.030 -0.018 -0.006 0.006 0.018 0.030

0.00

0.22

0.44

0.66

0.88

1.10

1.32

1.54

1.76

1.98

2.20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

TIME (s)

I_limit

Vclose_loop

21

LMP8646

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SNOSC63B – FEBRUARY 2012 – REVISED DECEMBER 2014

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Typical Applications (continued)

8.2.2.3 Application Curve

Figure 31. Plot for the Resistive Load Application With LMZ12003 Regulator Plot

8.2.3 Application #3: Current Limiter With a Low-Dropout Regulator and Resistive Load

Figure 32. Resistive Load Application With LP38501 Regulator

8.2.3.1 Design Requirements

This next example is the same as the last example, except that the regulator is now a low-dropout regulator, the

LP38501, as seen in Figure 32. For this example, we will let the open-loop current to be 1.25A and the close-

loop current, ILIMIT, to be 1A.

8.2.3.2 Detailed Design Procedure

Step 1: Choose the components for the Regulator.

Refer to the LP38501 application note (AN-1830) to select the appropriate components for the LP38501.

Step 2: Choose the sense resistor, RSENSE

RSENSE sets the voltage VSENSE between +IN and -IN and has the following equation:

RSENSE = VOUT / [(ILIMIT) * (RG / 5kOhm)]

(18)

In general, RSENSE depends on the output voltage, limit current, and gain. Refer to section Selection of the Sense

Resistor, RSENSE to choose the appropriate RSENSE value; this example uses 58 mOhm.

Step 3: Choose the gain resistor, RG, for LMP8646