AN4501 datasheet(31/48 Pages) STMICROELECTRONICS

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AN4501

Selection of the input capacitor

The substitution tON + tOFF by 1/FSW gives:

Equation 23:

Figure 14. Current waveforms of the input capacitor for a boost converter in CCM

Similarly to IL,PP, VCIN,PP reaches its maximum when the duty cycle is 50%.

7.1.2

Contribution of the capacitor ESR to the input voltage ripple

As the peak-to-peak current ripple of the input capacitor is equal to IL,PP, the input voltage

ripple caused by the ESRCIN is given by:

Here again, the worst case corresponds to a duty cycle of 50%.

Therefore:

7.2

Maximum input voltage ripple

The max input voltage ripple is the sum of

ΔVCIN,MAX and ΔVESR,CIN,MAX:

Equation 24:

CI N t

---------

OFF

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



---

LPP

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

OFF

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

CIN PP

LPP

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

ESR,CIN,PP

ESR

CIN

LPP

ESR,CIN,PP,MAX

ESR

CIN

LPP MAX

IN,PP,MAX

L,PP,MAX

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

ESR

CIN

LPP MAX

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