Diodes ZXLD1352 - Manual (Page 12)

ZXLD1352
ZXLD1352
Document number: DS33469 Rev. 3 - 2
12 of 21
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December 2010
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A Product Line of
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Application Information
Setting nominal average output current with external resistor R
S
The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (R
S
)
connected between V
IN
and I
SENSE
and is given by:
I
OUTnom
= 0.1/R
S
for R
S
>0.27
Ω
The table below gives values of nominal average output current for several preferred values of current setting resistor (R
S
) in the
typical application circuit shown on page 1:
R
S
(
Ω)
Nominal average output
current (mA)
0.27 370
0.3 333
0.33 300
0.39 256
The above values assume that the ADJ pin is floating and at a nominal voltage of V
REF
(=1.25V). Note that R
S
=0.27
Ω is the
minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value.
It is possible to use different values of R
S
if the ADJ pin is driven from an external voltage. (See next section).
Output current adjustment by external DC control voltage
The ADJ pin can be driven by an external dc voltage (V
ADJ
), as shown, to adjust the output current to a value above or below the
nominal average value defined by R
S
.
The nominal average output current in this case is given by:
I
OUTdc
= 0.08*V
ADJ
/R
S
[for 0.3< V
ADJ
<2.5V]
Note that 100% brightness setting corresponds to V
ADJ
= V
REF
. When driving the ADJ pin above 1.25V, R
S
must be increased in
proportion to prevent I
OUTdc
exceeding 370mA maximum.
The input impedance of the ADJ pin is 50k
Ω ±25%.
GND
ZXLD1352 ADJ
GND
+
DC