Diodes ZXLD1371 - Manual (Page 22)

ZXLD1371
ZXLD1371
Document number: DS35436 Rev. 1 - 2
22 of 42
www.diodes.com
February 2012
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A Product Line of
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Applications Information (cont.)
I
LED
= I
RS
1-D =
0.225
R
S
GI_ADJ
V
ADJ
V
REF
(Boost and Buck-boost) Equation 4
This shows that the LED current depends on the ADJ pin voltage, the reference voltage and 3 resistor values (RS, RGI1
and RGI2). It is independent of the input and output voltages.
If the ADJ pin is connected to the REF pin, this simplifies to
I
LED
=
0.225
R
S
GI_ADJ (Boost and Buck-boost)
Now I
LED
is dependent only on the 3 resistor values.
Considering power dissipation and accuracy, it is useful to know how the mean sense voltage varies with input voltage and
other parameters.
V
RS
= I
RS
R
S
= 0.225
GI_ADJ
1-D
V
ADJ
V
REF
(Boost and Buck-boost) Equation 5
This shows that the sense voltage varies with duty cycle in Boost and Buck-boost configurations.