ZXLD1352 查看數據表（PDF） - Zetex => Diodes

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ZXLD1352

350mA LED driver with internal switch and enhanced PWM dimming range

Zetex => Diodes 

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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