LM3502ITL-16 NSC [National Semiconductor], LM3502ITL-16 Datasheet - Page 13

• Manufacturer Part Number: LM3502ITL-16
• Description: Step-Up Converter for White LED Applications
• Manufacturer: NSC [National Semiconductor]

Application Information
WHITE LED CURRENT SETTING
The LED current is set using the following equation:
I
V
R1:
WHITE LED DIMMING
For dimming the white LED string with a pulse-width-
modulated (PWM) signal on the Cntrl pin, care must taken to
balance the tradeoffs between audible noise and white LED
If V
LED
Fb
: Feedback Pin Voltage. V
OUT2
: White LED Current.
Currrent Setting Resistor.
is not used , En2 must be grounded
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Fb
= 0.25V, Typical.
FIGURE 5.
13
brightness control. For best PWM duty cycle vs. white LED
current linearity, the PWM frequency should be between
200Hz and 500Hz. Other PWM frequencies can be used, but
the linearity over input voltage and duty cycle variation will
not be as good as what the 200Hz to 500Hz PWM frequency
spectrum provides. To minimize audible noise interference, it
is recommended that a output capacitor with minimal sus-
ceptibility to piezoelectric induced stresses be used for the
particular applications that require minimal or no audible
noise interference.
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