Zxld1374, Application information – Diodes ZXLD1374 User Manual
Page 24
ZXLD1374
Document number: DS35032 Rev. 3 - 2
24 of 39
September 2012
© Diodes Incorporated
ZXLD1374
A Product Line of
Diodes Incorporated
Application Information
(cont.)
Output Capacitor (cont.)
The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS
current rating. The minimum RMS current for the output capacitor is calculated as follows:
Buck
12
I
I
PP
LED
RMS
OUTPUT
−
−
=
Boost and Buck-Boost
D
1
D
I
I
MAX
MAX
LED
RMS
OUTPUT
−
=
−
Ceramic capacitors with X7R dielectric are the best choice due to their high ripple current rating, long lifetime, and performance over the voltage
and temperature ranges.
Input Capacitor
The input capacitor can be calculated knowing the input voltage ripple
ΔV
IN-PP
as follows:
Buck
( )
V
x
f
xI
D
1
Dx
C
PP
IN
SW
LED
IN
Δ
−
=
−
use D = 0.5 as worst case
Boost
V
x
Xf
8
I
C
PP
IN
SW
PP
L
IN
Δ
Δ
=
−
−
Buck-boost
V
x
f
DxI
C
PP
IN
SW
LED
IN
Δ
=
−
use D = D
MAX
as worst case
The minimum RMS current for the output capacitor is calculated as follows:
Buck
(
)
D
1
Dx
x
I
I
LED
RMS
CIN
−
=
−
use D = 0.5 as worst case
Boost
12
I
I
PP
L
RMS
CIN
−
−
=
Buck-Boost
D
1
D
x
I
I
LED
RMS
CIN
−
=
−
use D = D
MAX
as worst case