SPV1050 datasheet(33/36 Pages) STMICROELECTRONICS

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SPV1050

Application tips

Appendix A

Application tips

In DC-DC converters the energy is transferred from the input to the output through the

inductor. During the ON phase of the duty cycle, the inductor stores energy while during the

OFF phase of the duty cycle, the energy is released toward the output stage.

Figure 26. Inductor current and input voltage waveforms

The SPV1050 controls the duty cycle of the driving signal by comparing the voltages on the

MPP and MPP-REF pins. When VMPP rises higher than VMPP-REF, the IC switches ON and

the inductor is loaded for TON until one of the following events occurs:

–VSTORE triggers the EOC threshold

–

The inductor current (IL) triggers the internal threshold IL(PEAK) (= 140 mA, typ.)

–TON(MAX) = 10 µs elapses

The energy stored in the inductor will be released to the output stage during the OFF phase.

During TOFF, IL decreases to 0 mA (all energy has been released). According to the internal

controls of the IC, TOFF(MIN) = 0.2 µs then, in order to prevent IL becoming negative, the

application must be designed such that the energy stored in the inductor during TON is

always greater or equal to the energy released during TOFF. This goal can be achieved

through the proper selection of R2 + R3. Thus, in order to guarantee IL(MIN) > 0, it must be:

Equation 10

ILMIN



VSTORE VIN

–

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

TOFF MIN

 0





–

SPV1050 Datasheet(PDF) 33 Page - STMicroelectronics