LM3406/06HV

CS

+

-

One-shot

LED 1

LED n

0.2V

+

-

COMP

LM3406, LM3406HV, LM3406HV-Q1

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SNVS512E – SEPTEMBER 2008 – REVISED MARCH 2014

8 APPLICATION INFORMATION

8.1 THEORY OF OPERATION

The LM3406, LM3406HV and LM3406HV-Q1 are buck regulators with a wide input voltage range, low voltage

reference, and a fast output enable/disable function. These features combine to make them ideal for use as a

constant current source for LEDs with forward currents as high as 1.5A. The controlled on-time (COT)

architecture uses a comparator and a one-shot on-timer that varies inversely with input and output voltage

instead of a fixed clock. The LM3406 family also employs an integrator circuit that averages the output current.

When the converter runs in continuous conduction mode (CCM) the controlled on-time maintains a constant

switching frequency over changes in both input and output voltage. These features combine to give the LM3406

family an accurate output current, fast transient response, and constant switching frequency over a wide range of

conditions.

8.2 CONTROLLED ON-TIME OVERVIEW

shows a simplified version of the feedback system used to control the current through an array of LEDs. A

following simplified equation (for the most accurate version of this expression see the Appendix):

(1)

next cycle.

Comparator and One-Shot

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Product Folder Links: LM3406 LM3406HV LM3406HV-Q1