0

10

20

30

40

50

60

0

0.5

1

1.5

2

2.5

3

3.5

4

Current Limit Threshold (A)

1.016

25230 V

Iosmin

(mA)

RLIM

K

×

æ

ö

= ç

÷

× W

è

ø

0.977

23950 V

Iosnom

(mA)

RLIM

K

×

æ

ö

= ç

÷

× W

è

ø

0.94

22980 V

Iosmax

(mA)

RLIM

K

×

æ

ö

= ç

÷

× W

è

ø

TPS65281, TPS65281-1

SLVSBH7B – JULY 2012 – REVISED DECEMBER 2012

www.ti.com

Placing a high-value electrolytic capacitor on the output pin is recommended when large transient currents are

expected on the output.

Programming the Current-Limit Threshold

The over-current threshold is user programmable via an external resistor. The TPS65281/TPS65281-1 uses an

internal regulation loop to provide a regulated voltage on the RLIM pin. The current-limit threshold is proportional

to the current sourced out of RLIM. The recommended 1% resistor range for RLIM is 5 k

Ω ≤ RLIM ≤232 kΩ to

ensure stability of the internal regulation loop. Many applications require that the minimum current limit is above a

certain current level or that the maximum current limit is below a certain current level, so it is important to

consider the tolerance of the over-current threshold when selecting a value for RLIM. The following equations

and Figure 28 can be used to calculate the resulting over-current threshold for a given external resistor value

(RLIM). The traces routing the RLIM resistor to the TPS65281/TPS65281-1 should be as short as possible to

reduce parasitic effects on the current-limit accuracy.

RLIM can be selected to provide a current-limit threshold that occurs 1) above a minimum load current or

2) below a maximum load current.

Current-Limit Threshold Equations (IOS):

(1)

(2)

(3)

Where 15 k

Ω ≤ RLIM ≤ 232 kΩ.

While the maximum recommended value of RLIM is 232 k

Ω, there is one additional configuration that allows for a

lower current-limit threshold. The RLIM pin may be connected directly to SW_IN to provide a 1.2 A (typ) current-

limit threshold. Additional low-ESR ceramic capacitance may be necessary from SW_IN to AGND in this

configuration to prevent unwanted noise from coupling into the sensitive RLIM circuitry.

16

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