DocID18279 Rev 5

27/37

ST1CC40

Application information

37

The pulse-by-pulse current limitation is effective in implementing constant current protection

when:

Equation 38

From Equation 36 and Equation 37 we can gather that the implementation of the constant

In fact, in short-circuit condition the voltage applied to the inductor during the off-time

becomes equal to the voltage drop across parasitic components (typically the DCR of the

In general, the worst case scenario is heavy short-circuit at the output with maximum input

voltage. Equation 36 and Equation 37 in overcurrent conditions can be simplified to:

Equation 39

Equation 40

At higher input voltage,

may escalate. As a consequence, the system typically meets Equation 38 at a current level

higher than the nominal value thanks to the increased voltage drop across stray

components. In most of the application conditions the pulse-by-pulse current limitation is

effective to limit the inductor current. Whenever the current escalates, a second level current

protection called “Hiccup mode” is enabled. 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. If the hiccup current level (6.2 A typ.)

is triggered, the switching activity is prevented for 12 cycles.

Figure 15 shows the operation of the constant current protection when a short-circuit is

applied at the output at the maximum input voltage.





=

DCR

R

I

V



+

 I



–

L



L

--------- 90ns





=



+



–

I



L

–



+



–

I



L

--------------------------------------------------------------- 1,18

s





=