ZXLD1370_11 DIODES [Diodes Incorporated], ZXLD1370_11 Datasheet - Page 22

• Manufacturer Part Number: ZXLD1370_11
• Description: 60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER
• Manufacturer: DIODES [Diodes Incorporated]

ZXLD1370
Document number: DS32165 Rev. 3 - 2
Applications Information
Boost and Buck-boost
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
Boost and Buck-boost
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
Buck
Boost
Buck-boost
The minimum RMS current for the output capacitor is calculated as follows:
Buck
Boost
Buck-boost
where:
•
•
•
•
C
I
I
C
C
C
I
I
I
COUTPUT
COUTPUT
CIN
CIN
CIN
IN
IN
IN
OUTPUT
ΔI
ΔI
f
r
−
−
−
sw
datasheet of the LED manufacturer).
LED
=
=
RMS
RMS
RMS
=
L
LED
D
8
f
is the switching frequency (From graphs and calculator)
is the ripple of the inductor current, usually ± 20% of the average sensed current
SW
f
f x
is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the
−
−
SW
=
=
=
x
RMS
=
RMS
is the ripple of the LED current, it should be <40% of the LEDs average current
D
1 (
I
I
SW
x
LED
LED
I
f
x
L
I x
Δ
−
SW
12
Δ
−
=
=
Δ
I
PP
D
x
LED
x
L
V
x
V
−
I
r x
)
Δ
IN
LED
I
PP
D
IN
I x
LED
Dx
−
V
1 (
−
LED
PP
I x
12
LED
PP
IN
−
−
D
1 (
−
LED
PP
1
PP
D
x
−
D
−
)
Δ
−
D
D
PP
MAX
I
LED
)
MAX
Use D=D
(Continued)
−
PP
Use D = 0.5 as worst case
Use D = D
use D=0.5 as worst case
MAX
as worst case
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MAX
22 of 35
as worst case
IN-PP
as follows:
Diodes Incorporated
A Product Line of
© Diodes Incorporated
ZXLD1370
February 2011