744770933 データシートの表示（PDF） - Diodes Incorporated.
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744770933 Datasheet PDF : 33 Pages
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Diodes Incorporated
Buck
I = COUTPUT − RMS
ILED−PP
12
Boost and Buck-boost
ZXLD1370
ICOUTPUT −RMS = ILED
DMAX
1− DMAX
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 ΔVIN-PP as follows:
Buck
CIN
=
D x(1− D)xILED
fSW x ΔVIN−PP
Use D = 0.5 as worst case
Boost
CIN
=
ΔIL−PP
8x fSW x ΔVIN−PP
Buck-boost
CIN
=
D x ILED
fSW x ΔVIN−PP
Use D = DMAX as worst case
The minimum RMS current for the output capacitor is calculated as follows:
Buck
ICIN−RMS = ILED x Dx(1− D)
Boost
ICIN−RMS =
IL −PP
12
Buck-boost
use D=0.5 as worst case
ICIN−RMS = ILED x
D
(1− D)
Use D=DMAX as worst case
PWM OUTPUT CURRENT CONTROL & DIMMING
The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with
up to 1000:1 resolution; however higher dimming frequencies can be used – at the expense of dimming dynamic range and
accuracy.
Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is
better than 1% for PWM from 5% to 100%. This is shown in the graph below:
ZXLD1370
Document number: DS32165 Rev. 2 - 2
21 of 33
www.diodes.com
May 2010
© Diodes Incorporated
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