Datasheet

( )
RLIM,max TOL
LIM,min
201.9
R 1 R
I 0.44
= - ´
+
( )
RLIM,min TOL
LIM,max
201.9
R 1 R
I 0.38
= + ´
-
LIM,max
RLIM,min
201.9
I 0.38
R
= +
LIM,min
RLIM,max
201.9
I 0.44
R
= -
( )
RFLT,max TOL
FAULT,min
185.58
R 1 R
I 0.13
= - ´
+
( )
RFLT,min TOL
FAULT,max
213.68
R 1 R
I 0.13
= + ´
-
FAULT,max
RFLT,min
213.68
I 0.13
R
= +
FAULT,min
RFLT,max
185.58
I 0.13
R
= -
TPS2590
www.ti.com SLUS960G –JULY 2009–REVISED JANUARY 2014
Overcurrent Shutdown
Overcurrent shutdown occurs when the output current exceeds I
FAULT
for the duration of the fault timer. Figure 8
shows a step rise in output current which exceeds the I
FAULT
threshold but not the I
LIM
threshold. The increased
current is on for the duration of the timer. When the timer expires, the output is turned off.
Programming the Fault (I
FAULT
) and Current-limit (I
LIM
) Thresholds
The I
FAULT
and I
LIM
thresholds are user programmable with an external resistor. The TPS2590 device uses an
internal regulation loop to provide a regulated voltage on the IFLT and ILIM pins. The current-limit thresholds are
proportional to the current sourced out of IFLT and ILIM. The recommended 1% resistor range is 49.9 kΩ ≤ R
RFLT
≤ 200 kΩ and 40.2 kΩ ≤ R
RLIM
≤ 100 kΩ to ensure the rated accuracy. Many applications require that minimum
fault and current-limits are known or that maximum current-limit is bounded. It is important to consider the
tolerance of the fault and current-limit thresholds, as well as R
RFLT
and R
RLIM
when selecting values. See the
ELECTRICAL CHARACTERISTICS table for specific fault and current-limit settings.
Using the data for I
FAULT
and I
LIM
from the ELECTRICAL CHARACTERISTICS table, equations can be generated
and used for other set points. Equation 13 and Equation 14 are used to calculate minimum and maximum I
FAULT
where R
RFLT,max
and R
RFLT,min
include R
RFLT
tolerances. Equation 15 and Equation 16 calculate R
RFLT,max
and
R
RFLT,min
where R
TOL
is the 1% resistor tolerance.
(13)
(14)
(15)
(16)
Equation 17 and Equation 18 are used to calculate minimum and maximum I
LIM
where R
RLIM,max
and R
RLIM,min
include R
RLIM
tolerances. Equation 19 and Equation 20 calculate R
RLIM,max
and R
RLIM,min
where R
TOL
is the 1%
resistor tolerance.
(17)
(18)
(19)
(20)
Design Example
A typical design is shown in Figure 18 with the following requirements:
• Nominal input voltage, V
IN
: 12 V
• Maximum expected load current, I
OUT
: 3.7 A
• Load capacitance, C
LOAD
: 100 µF
• Expected resistive load, R
LOAD
during start-up: 13 Ω
• Current-limit, I
LIM, min
: > I
FAULT, max
• Example calculations are shown in the TPS2590 Design Calculator Tool (SLUC398).
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