Datasheet

Components selection PM6641
36/47 Doc ID 13510 Rev 3
Once the inductor value is determined, the inductor current ripple is then recalculated:
Equation 13
The next step is the computation of the maximum RMS inductor current:
Equation 14
The inductor must have an RMS current greater than I
L,RMS
in order to assure thermal
stability.
Then the calculation of the maximum inductor peak current follows:
Equation 15
I
L,PEAK
is important when choosing the inductor, in term of its saturation current.
The saturation current of the inductor should be greater than the maximum between I
Lpeak
and the programmed peak current limit, selected by an external resistor connected between
CSNS pin and AGND (as described in
current limit section).
8.2 Input capacitor selection
In a buck topology converter the current that flows through the input capacitor is pulsed and
with zero average value. The RMS input current, for each switching regulator, can be
calculated as follows:
Equation 16
Neglecting the second term, the equation is reduced to:
Equation 17
MAX,IN
OUT
OUTMAX,IN
MAX,L
V
V
Lfsw
VV
I ⋅
⋅
−
=Δ
12
)I(
)I(I
2
MAX,L
2
MAX,LOADRMS,L
Δ
+=
2
I
II
MAX,L
MAX,LOADPEAK,L
Δ
+=
2
L
2
LOAD
RMS
Cin
)I(D
12
1
)D1(DII Δ⋅+−⋅⋅=
)D1(DII
LOAD
RMS
Cin
−⋅≅