ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

ZXLD1350

Document number: DS33468 Rev. 8 - 2

12 of 22

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March 2011

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Application Information

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 > 0.27Ω]

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(Ω)

Nominal average output

current (mA)

0.27

370

0.30

333

0.33

300

0.39

256

The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V). Note that RS = 0.27V 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.

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 200k

Ω ±25%.

 

GND

ZXLD1350

ADJ

+

DC

GND