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
SLUS960F –JULY 2009–REVISED MAY 2013 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 >
2V) turns off and can be restarted by cycling power or toggling the EN signal. A device operating in retry mode
(RTRY < 0.8V) 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 ~1.6 × I
LIM
the TPS2590 immediately shuts off current
to the load without waiting for the fault timer to expire. After such a shutoff the TPS2590 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 goes into current
limit during the restart attempt and either latches off or attempts retry depending on the state of the RTRY input.
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.
12 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated
Product Folder Links: TPS2590