LED5000 datasheet(34/52 Pages) STMICROELECTRONICS

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Application notes - alternative topologies

LED5000

34/51

Doc ID 023951 Rev 1

Application notes - alternative topologies

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

enhanced dimming capability, the LED5000 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, which is the voltage drop across the LEDs and the sensing resistor.

The inverting buck-boost (see

Figure 23) requires the same component count as the buck

conversion and it is more efficient than the positive buck-boost. 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 50

so:

Equation 51

where VOUT<0.

Figure 23.

Inverting buck-boost

Example 1

VIN RANGE=12-24 V, VFW_LED=3.7 V, nLED= 5 so VOUT=18.7 V

IN_MAX LED5000

OUT

–

IN_MAX LED5000

OUT

VIN

REF

ISW

AM13507v1

LED5000 Datasheet(PDF) 34 Page - STMicroelectronics