Datasheet
LOAD_TOL CT_TOL ON
CT
(1 C C ) t
C
40000
+ + ´
=
ILOAD
VOUT
CT
2V/div
0.5V/div
1A/div
5V/div
5ms/div
FLT
TPS2590
SLUS960G –JULY 2009–REVISED JANUARY 2014
www.ti.com
Figure 17. Fault Timer Operation During Start-Up
C
CT
can be chosen for fault-free start-up including expected C
LOAD
and C
CT
capacitance tolerance as shown in
Equation 12.
(12)
Normal Operation
When load current exceeds I
FAULT
during normal operation the fault timer starts. If load current drops below I
FAULT
before the fault timer expires, normal operation continues. If load current stays above the I
FAULT
threshold the
fault timer expires and a fault is declared. When a fault is declared a device operating in latched mode (RTRY >
2 V) turns off and can be restarted by cycling power or toggling the EN signal. A device operating in retry mode
(RTRY < 0.8 V) attempts to turn on at a 3.7% duty cycle until the fault is cleared. When I
LIM
is reached during a
fault the device goes into current-limit and the fault timer keeps running.
Start-Up into a Short
The controller attempts to power on into a short for the duration of the timer. Figure 13 shows a small current
resulting from power limiting the internal MOSFET. This happens only once in latched mode. In Retry mode, the
cycle repeats at a 3.7% duty cycle.
Shutdown Modes
Hard Overload - Fast Trip
When a hard overload causes the load current to exceed approximately 1.6 × I
LIM
the TPS2590 device
immediately shuts off current to the load without waiting for the fault timer to expire. After such a shutoff the
TPS2590 device enters startup mode and attempts to apply power to the load. If the hard overload was caused
by a transient, then normal startup can be expected. If the hard overload is caused by a persistent, continuous
failure then the TPS2590 device goes into current-limit during the restart attempt and either latches off or
attempts retry depending on the state of the RTRY input.
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