ST1S14 datasheet(29/46 Pages) STMICROELECTRONICS

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ST1S14

Application information

so the output voltage is:

Equation 34

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

Equation 35

considering TON which has already been reduced to its minimum.

Equation 36

where TSW=1/fSW and considering the nominal fSW.

The voltage divider introduces a gain factor K between the VO_SET and VFB that affect the

effectiveness of the current protection. The worst case scenario is the minimum K, that is

the minimum output voltage, over the input voltage (Chapter 5.2: Minimum output voltage

over VIN range).

As a consequence the minimum feedback voltage to keep the inductor current limited over

the input voltage range can be expressed making Equation 35 equal to Equation 36 and

expressing VO_SET as given in Equation 1:

Equation 37

Equation 37 expresses the worst case scenario as it considers the minimum K gain of the

voltage divider over the entire input voltage range. The Figure 16 plots the Equation 37

considering the minimum value of the peak current limit given in Table 6: Electrical

characteristics on page 8.

-------

⎝⎠

⎛⎞

⋅

O_SET

1.22

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

⋅

L TON

DCR

DSON

() I

⋅

–

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

ON MIN

()

--------- 90ns

()

≅

L TOFF

O_MIN

DCR

⋅

()

–

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

90ns

–

()

O_SET

1.22

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

⋅

DCR

⋅

⎝⎠

⎛⎞

–

-------------------------------------------------------------------------------------------- 1.18

μs

()

≅

FB VIN

()

1.22

⋅

ON_MIN

⋅

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

DCR

⋅

()

⋅

⎝⎠

⎛⎞

–

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