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LM3406, LM3406HV, LM3406HV-Q1

SNVS512E – SEPTEMBER 2008 – REVISED MARCH 2014

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8.3 SWITCHING FREQUENCY

The LM3406 family does not contain a clock, however the on-time is modulated in proportion to both input

(2)

(3)

(4)

(5)

The LM3406 family regulators should be operated in continuous conduction mode (CCM), where inductor current

stays positive throughout the switching cycle. During steady-state CCM operation, the converter maintains a

constant switching frequency that can be estimated using the following equation (for the most accurate version,

particularly for applications that will have an input or output voltage of less than approximately 12V, see the

Appendix):

(6)

(7)

8.4 SETTING LED CURRENT

the output averaging:

(8)

8.5 MAXIMUM NUMBER OF SERIES LEDS

LED driver designers often want to determine the highest number of LEDs that can be driven by their circuits.

can provide. A buck regulator cannot provide an output voltage that is higher than the minimum input voltage,

calculated as:

(9)

espression and rounding down:

(10)

nearly equal to input voltage, and this can allow the system to drive more LEDs in series. Low switching

frequencies are not always desireable, however, because they require larger, more expensive components.

8.6 CALCULATING OUTPUT VOLTAGE

Even though output current is the controlled parameter in LED drivers, output voltage must still be calculated in

order to design the complete circuit. Referring to the illustration in , output voltage is calculated as:

(11)

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