OS(max)

0.93

ILIM

27,570 V

I

(mA)

R

k

=

W

OS(typ)

0.998

ILIM

28,235 V

I

(mA)

R

k

=

W

OS(min)

1.114

ILIM

32,114 V

I

(mA)

R

k

=

W

TPS2500, TPS2501

SLVS886C – OCTOBER 2008 – REVISED AUGUST 2010

www.ti.com

Programming the Current-Limit Threshold Resistor RILIM

The overcurrent threshold is user programmable via an external resistor. The TPS2500 uses an internal

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

current sourced out of ILIM. The recommended 1% resistor range for RILIM is 16.1 kΩ ≤ RILIM ≤ 200 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 overcurrent threshold when selecting a value for RILIM. The following equations and Figure 13

can be used to calculate the resulting overcurrent threshold for a given external resistor value ®ILIM). Figure 13

includes current-limit tolerance due to variations caused by temperature and process. However, the equations do

not account for tolerance due to external resistor variation, so it is important to account for this tolerance when

selecting RILIM. The traces routing the RILIM resistor to the TPS2500 should be as short as possible to reduce

parasitic effects on the current-limit accuracy.

RILIM can be selected to provide a current-limit threshold that occurs 1) above a minimum load current or 2)

below a maximum load current.

To design above a minimum current-limit threshold, find the intersection of RILIM and the maximum desired load

current on the IOS(min) curve and choose a value of RILIM below this value. Programming the current limit above a

minimum threshold is important to ensure start up into full load or heavy capacitive loads. The resulting maximum

current-limit threshold is the intersection of the selected value of RILIM and the IOS(max) curve.

To design below a maximum current-limit threshold, find the intersection of RILIM and the maximum desired load

current on the IOS(max) curve and choose a value of RILIM above this value. Programming the current limit below a

maximum threshold is important to avoid current-limiting upstream power supplies, causing the input voltage bus

to droop. The resulting minimum current-limit threshold is the intersection of the selected value of RILIM and the

IOS(min) curve.

Current-limit threshold equations (IOS):

16

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