ZXLD1356QDACTC datasheet(17/28 Pages) DIODES

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ZXLD1356Q

Document number: DS37077 Rev. 2 - 2

17 of 28

www.diodes.com

October 2015

ZXLD1356Q

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 = 0.2/RS [for RS  0.36Ω]

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)

0.36

555

0.56

357

1.33

150

The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (= 1.25V). Note that RS = 0.36V 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 = (VADJ /1.25) x (0.2/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 550mA maximum.

The input impedance of the ADJ pin is 50kΩ ±25% for voltages below VREF and 14.2kΩ ±25% for voltages above VREF +100mV.

Output Current Adjustment by PWM Control

Directly Driving ADJ Input

A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as shown below, to adjust the output current to a

value above or below the nominal average value set by resistor RS:

ZXLD1356QDACTC Datasheet(PDF) 17 Page - Diodes Incorporated