ST1S14 datasheet(32/46 Pages) STMICROELECTRONICS

32 / 46 page

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 VFB for effective pulse-by-pulse protection over VIN

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.

FB VIN

()

1.22

-----------

1.22

⋅

ON_MIN

⋅

--------------------------------------

DCR

⋅

()

⋅

⎝⎠

⎛⎞

–

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