ST1S14 datasheet(31/46 Pages) STMICROELECTRONICS

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ST1S14

Application information

prevented for 16 ms and then a new soft-start phase takes place (see Figure 17).

7.4.2

VFB < 300 mV

The device reduces the switching frequency by five times the nominal value when VFB<300

mV. The frequency foldback makes the pulse-by-pulse current protection effective to keep

the current limited when the output voltage is shorted and VOUT negligible.

Equation 29 and 30 in overcurrent conditions can be simplified to:

Equation 38

considering TON which has already been reduced to its minimum.

Equation 39

taking into consideration the frequency foldback feature.

Figure 18. Current and frequency foldback triggered when VFB<300 mV (red trace)

The content given in Section 7.4.1 is valid and the equivalent expression of Equation 37 is:

L TON

DCR

DSON

() I

⋅

–

------------------------------------------------------------------- T

ON MIN

()

--------- 90ns

()

≅

L TOFF

O_MIN

DCR

⋅

()

–

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

-----------

90ns

–

⎝⎠

⎛⎞

O_SET

1.22

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

⋅

DCR

⋅

⎝⎠

⎛⎞

–

-------------------------------------------------------------------------------------------- 5.9

μs

()

≅

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