The LM3433 is an adaptive constant on-time DC/DC buck (step-down) constant current
controller (a true current source). The LM3433 provides a constant current for illuminating high
power LEDs. The output configuration allows the anodes of multiple LEDs to be tied directly to the
ground referenced chassis for maximum heat sink efficacy. The high frequency capable architecture
allows the use of small external passive components and no output capacitor while maintaining low
LED ripple current. Two control inputs are used to modulate LED brightness. An analog current
control input is provided so the LM3433 can be adjusted to compensate for LED manufacturing
variations and/or color temperature correction. The other input is a logic level PWM control of LED
current. The PWM functions by shorting out the LED with a parallel switch allowing high PWM dimming
frequencies. High frequency PWM dimming allows digital color temperature control, interference
blanking, field sequential illumination, and brightness control. Additional features include
thermal shutdown, VCC under-voltage lockout, and logic level shutdown mode.
The LM3433 is available in a low profile 24-pin WQFN package.
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