Datasheet
Application information ST1S14
32/46 DocID17977 Rev 2
Equation 40
The Figure 19 plots the Equation 40 considering the foldback current limitation threshold
(1.45A) given in Table 6: Electrical characteristics which is active out of the soft start time.
Equation 40 expresses the worst case scenario as it considers the minimum K gain of the
voltage divider over the entire input voltage range (see Figure 14).
In most of the application conditions the pulse by pulse current limitation with frequency
foldback is effective to limit the inductor current in short circuit condition. The current
foldback helps to decrease the power component stress in persistent short circuit condition
out of the sift start time.
The hiccup protection offers an additional protection against heavy short circuit condition at
very high input voltage even considering the spread of the minimum conduction time of the
power element. In case the hiccup current level (6.2 A typical) is triggered the switching
activity is prevented for 15 ms and then a new soft start phase takes place.
Figure 19. Minimum V
FB
for effective pulse-by-pulse protection over V
IN
Figure 20 shows the effectiveness of the constant current protection limiting the inductor
current to the peak current of 1.45 A typ. during a short circuit event.
V
FB
V
IN
()
1.22
5
-----------
1.22 T
SW
⋅
V
IN
T
ON_MIN
⋅
--------------------------------------
V
D
I
L
DCR⋅()+()⋅
⎝⎠
⎛⎞
–=
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