Datasheet

Application notes - alternative topologies LED5000
34/51 Doc ID 023951 Rev 1
6 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
V
IN
and V
OUT
(<0). As a consequence:
Equation 50
so:
Equation 51
where V
OUT
<0.
Figure 23. Inverting buck-boost
Example 1
V
IN RANGE
=12-24 V, V
FW_LED
=3.7 V, n
LED
= 5 so V
OUT
=18.7 V
V
IN_MAX LED5000
V
IN
V
OUT
–=
V
IN
V
IN_MAX LED5000
V
OUT
+ 48 V
OUT
+==
V
IN
V
REF
I
SW
AM13507v1