Datasheet

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 R
ILIM
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 R
ILIM
is 16.1 kΩ ≤ R
ILIM
≤ 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 R
ILIM
. 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 R
ILIM
. The traces routing the R
ILIM
resistor to the TPS2500 should be as short as possible to reduce
parasitic effects on the current-limit accuracy.
R
ILIM
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 R
ILIM
and the maximum desired load
current on the I
OS(min)
curve and choose a value of R
ILIM
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 R
ILIM
and the I
OS(max)
curve.
To design below a maximum current-limit threshold, find the intersection of R
ILIM
and the maximum desired load
current on the I
OS(max)
curve and choose a value of R
ILIM
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 R
ILIM
and the
I
OS(min)
curve.
Current-limit threshold equations (I
OS
):
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