Datasheet
0.0 0.2 0.4 0.6 0.8 1.0 1.2
5
10
15
20
25
30
35
40
45
INPUT VOLTAGE (v)
SHORT CIRCUIT VOLTAGE (v)
SAFE OPERATING AREA
0.0 0.2 0.4 0.6 0.8 1.0 1.2
5
10
15
20
25
30
35
40
45
INPUT VOLTAGE (v)
SHORT CIRCUIT VOLTAGE (v)
SAFE OPERATING AREA
0.0 0.2 0.4 0.6 0.8 1.0 1.2
5
10
15
20
25
30
35
40
45
INPUT VOLTAGE (v)
SHORT CIRCUIT VOLTAGE (v)
SAFE OPERATING AREA
LM22672
SNVS588L –SEPTEMBER 2008–REVISED APRIL 2013
www.ti.com
If the input voltage should exceed this value, while in foldback mode, the regulator and/or the diode may
be damaged. It is important to note that the voltages in these equations are measured at the inductor. Normal
trace and wiring resistance will cause the voltage at the inductor to be higher than that at a remote load.
Therefore, even if the load is shorted with zero volts across its terminals, the inductor will still see a finite voltage.
It is this value that should be used for V
x
and V
sc
in the calculations. In order to return from foldback mode, the
load must be reduced to a value much lower than that required to initiate foldback. This load "hysteresis" is a
normal aspect of any type of current limit foldback associated with voltage regulators.
If the frequency synchronization feature is used, the current limit frequency fold-back is not operational, and the
system may not survive a hard short-circuit at the output.
The safe operating areas, when in short circuit mode, are shown in Figure 15 through Figure 17, for different
switching frequencies. Operating points below and to the right of the curve represent safe operation. Note that
these curves are not valid when the LM22672 is in frequency synchronization mode.
Figure 15. SOA at 300 kHz Figure 16. SOA at 500 kHz
Figure 17. SOA at 800 kHz
Soft-Start
The soft-start feature allows the regulator to gradually reach steady-state operation, thus reducing start-up
stresses. The internal soft-start feature brings the output voltage up in about 500 µs. This time can be extended
by using an external capacitor connected to the SS pin. Values in the range of 100 nF to 1 µF are recommended.
The approximate soft-start time can be estimated from the following equation:
(8)
Soft-start is reset any time the part is shut down or a thermal overload event occurs.
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