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2016-03-0004

PT0489-5

04/29/16

10

PI5PD2560/2561

Dual Channel,

Adjustable Current-Limited Power Switch

APPLICATION 2: DESIGNING BELOW A MAXIMUM CURRENT LIMIT

Some applications require that current limiting must occur below a certain threshold. For this example, assume that the desired

upper current-limit threshold must be below 1000 mA to protect an up-stream power supply. Use the IOS equations and Figure 9

to select RILIM.

Select the closest 1% resistor greater than the calculated value: RILIM = 63.4 kΩ. This sets the maximum current-limit threshold

at 1000 mA. Use the IOS equations, Figure 9, and the previously calculated value for RILIM to calculate the minimum resulting

current-limit threshold





The resulting minimum current-limit threshold is 765 mA with a 63.4 kΩ resistor.

ACCOUNTING FOR RESISTOR TOLERANCE

the current-limit threshold tolerance. The analysis focused only on the PI5PD2560A/2561A performance and assumed an exact

resistor value. However, resistors sold in quantity are not exact and are bounded by an upper and lower tolerance centered around

level. The following table shows a process that accounts for worst-case resistor tolerance assuming 1% resistor values. Step one

follows the selection process outlined in the application examples above. Step two determines the upper and lower resistance

bounds of the selected resistor. Step three uses the upper and lower resistor bounds in the IOS equations to calculate the threshold

limits. It is important to use tighter tolerance resistors, e.g. 0.5% or 0.1%, when precision current limiting is desired.

Desired Nominal

Current Limit

(mA)

Ideal

Resistor

(kΩ)

Closest 1%

Resistor

(kΩ)

Resistor Tolerance

Actual Limits

1% low

(kΩ)

1%

high(kΩ)

IOS MIN

(mA)

IOS Nom

(mA)

IOS MAX

(mA)

300

186.7

187

185.1

188.9

241.6

299.5

357.3

400

140

140

138.6

141.4

328

400

471.4

600

93.3

93.1

92.2

94

504.6

601.5

696.5

800

70

69.8

69.1

70.5

684

802.3

917.6

1000

56

56.2

55.6

56.8

859.9

996.4

1129.1

1200

46.7

46.4

45.9

46.9

1052.8

1206.9

1356.3

1400

40

40.2

39.8

40.6

1225

1393

1555.9

1600

35

34.8

34.5

35.1

1426.5

1609.2

1786.2

1800

31.1

30.9

30.6

31.2

1617.3

1812.3

2001.4

2000

28

28

27.7

28.3

1794.7

2000

2199.3

2200

25.5

25.5

25.2

25.8

1981

2196.1

2405.3

2400

23.3

23.2

23

23.4

2188.9

2413.8

2633

2600

21.5

21.5

21.3

21.7

2372.1

2604.7

2831.9

2800

20

20

19.8

20.2

2560.4

2800

3034.8

52850V

52850V

1

0.957

61200V

61200V

63.4