7447714101 datasheet(9/13 Pages) UNIONSEMI

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UM1360

Applications 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≥0.1Ω]

The table below gives values of nominal average output current for several preferred values of

current setting resistor (Rs) in the typical application circuit as shown on page 5.

Rs (Ω)

Nominal Average Output Current (mA)

0.1

1000

0.13

760

0.15

667

0.3

333

The above values assume that the VSET pin is floating or applied with a voltage higher than

2.5V (must be less than 5V). Note that Rs=0.1Ω 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 VSET pin is driven from an external voltage.

(See next section).

Output Current Adjustment by External DC Control Voltage

The VSET pin can be driven by an external DC voltage (VEN), as shown, to adjust the output

current to a value below the nominal average value defined by Rs.

Rs 0.13Ω

μH

μF

VIN (6V-40V)

VIN

VSET

ISENSE

UM1360

LED

The average output current is given by:

IOUT=(0.1*VEN)/(2.5*Rs) [for 0.3V<VEN<2.5V]

Note that 100% brightness setting corresponds to:

(2.5V≤VEN≤5V)

Output Current Adjustment by PWM Control

A Pulse Width Modulated (PWM) signal with duty cycle PWM can be applied to the VSET

pin, as shown below, to adjust the output current to a value below the nominal average value

set by resistor Rs:

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