LED6000 datasheet(35/49 Pages) STMICROELECTRONICS

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LED6000

Application notes - alternative topologies

Thanks to the wide input voltage range and the adjustable compensation network, the

LED6000 device is suitable to implement boost and buck-boost topologies.

6.1

Inverting buck-boost

The buck-boost topology fits the application with an input voltage range that overlaps the

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

The inverting buck-boost (see Figure 22) requires the same components count as the buck

conversion and it is more efficient than the positive buck-boost, since no additional power

MOSFET is required.

Figure 22. Inverting buck-boost topology

A current generator based on this topology implies two main application constraints:



The output voltage is negative so the LEDs must be reversed



The device GND floats with the negative output voltage. The device is supplied

between VIN and VOUT (< 0). As a consequence:

Equation 27

VIN,MAX = 61 V is the maximum operating input voltage for the LED6000, as shown in

Table 5 on page 8.

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

on-time interval, D, is given by:

Equation 28

However, due to power losses (mainly switching and conduction losses), the real duty cycle

is always higher than this. The real value (which can be measured in the application) should

be used in the following formulas.

MAX

OUT





OUT





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