LED6000PHR datasheet(41/49 Pages) STMICROELECTRONICS

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LED6000

Application notes - alternative topologies

6.3

Floating boost

The floating-boost topology fits the application with an input voltage range always lower than

the output voltage, VOUT, which is the voltage drop across the LEDs and the sensing

resistor. The floating boost (see Figure 30) requires the same components count as the

buck conversion.

Figure 30. Floating-boost topology

In this topology the output voltage is referred to VIN and not to GND. The device is supplied

by VOUT as a consequence the maximum voltage drop across the LEDs string is 61 V.

In floating-boost topology working in the continuous conduction mode (CCM), the HS MOS

on-time interval, D, is given by:

Equation 35

However, due conduction losses, the real duty cycle is always higher than the ideal one.

The real value should be used in the following formulas.

The peak current flowing in the embedded switch is:

Equation 36

While its average current level is equal to:

Equation 37

This is due to the fact that the current flowing through the internal power switch is delivered

to the output only during the OFF phase.

OUT





OUT

RIPPLE

OUT















OUT





LED6000PHR Datasheet(PDF) 41 Page - STMicroelectronics