R5973AD datasheet(27/38 Pages) STMICROELECTRONICS

27 / 38 page

DocID027027 Rev 1

27/38

R5973AD

Application information

considering TON that has been already reduced to its minimum.

Equation 31

considering that fSW has been already reduced to one third of the nominal.

In case a short-circuit at the output is applied and VIN = 12 V the inductor current is

controlled in most of the applications (see Figure 15). When the application must sustain the

short-circuit condition for an extended period, the external components (mainly the inductor

and diode) must be selected based on this value.

In case the VIN is very high, it could occur that the ripple current during TOFF (Equation 31)

does not compensate the current increase during TON(Equation 30). Figure 17 shows an

example of a power-up phase with VIN = VIN MAX = 36 V whereIL TON > IL TOFF, so the

current escalates and the balance between Equation 30 and Equation 31 occurs at a current

slightly higher than the current limit. This must be taken into account in particular to avoid

the risk of an abrupt inductor saturation.

Figure 15. Short-circuit current VIN = 12 V

IL TOFF



VD Vout DCRL I





–

--------------------------------------------------------------- 3T





VD Vout DCRL I





–

--------------------------------------------------------------- 6

s





R5973AD Datasheet(PDF) 27 Page - STMicroelectronics