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LED7707 Application information
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6.4.4 Output capacitor choice
The choice of the output capacitor is mainly affected by the desired output voltage ripple.
Since the voltage across the LEDs can be considered almost constant, this ripple is
transferred across the current generators, affecting their dynamic response.
The output ripple can be estimated as (neglecting the contribution of ESR of C
OUT
, very low
in case of MLCC):
Equation 31
where I
L, peak
is the inductor peak current (see Figure 21) calculated as:
Equation 32
whereas D, working in DCM, is:
Equation 33
defining M as:
Equation 34
Figure 21. Inductor current in DCM operation
(
)
`
C2
TII
V
OUT
OFFOUTpeak,L
OUT
⋅
⋅−
=Δ
⎩
⎨
⎧
=
=
=
⋅
⋅
=
V2.13V@A762.1
V8.10V@A915.1
LF
DV
I
max,IN
min,IN
sw
IN
peak,L
⎩
⎨
⎧
=
=
=
−⋅⋅⋅
=
V2.13V@414.0
V8.10V@55.0
R
)1M(MLF2
D
max,IN
min,IN
0
sw
⎩
⎨
⎧
=
=
=
V2.13V@015.2
V8.10V@463.2
V
V
M
max,IN
min,IN
IN
OUT
I
L, peak
I
L
t
T
SW
= 1/F
SW
T
ON
T
OFF
AM00593v1