ZXLD1352
Application notes
Setting nominal average output current with external resistor RS
The nominal average output current in the LED(s) is determined by the value of the external
current sense resistor (RS) connected between VIN and ISENSE and is given by:
IOUTnom = 0.1/RS [for RS>0.27⍀]
The table below gives values of nominal average output current for several preferred values of
current setting resistor (RS) in the typical application circuit shown on page 1:
RS (⍀)
0.27
0.3
0.33
0.39
Nominal average
output current (mA)
370
333
300
256
The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V).
Note that RS=0.27⍀ 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 RS 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 (VADJ), as shown, to adjust the output current
to a value above or below the nominal average value defined by RS.
+
DC
ADJ
ZXLD1352
GND
GND
The nominal average output current in this case is given by:
IOUTdc = 0.08*VADJ/RS [for 0.3< VADJ <2.5V]
Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above
1.25V, RS must be increased in proportion to prevent IOUTdc exceeding 370mA maximum.
The input impedance of the ADJ pin is 50k⍀ ±25%.
Issue 1 - August 2008
13
© Diodes Incorporated 2008
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