Datasheet
Table Of Contents
- Figure 1. Typical application circuit
- 1 Pin settings
- 2 Maximum ratings
- 3 Electrical characteristics
- 4 Functional description
- 5 Application notes - buck conversion
- 5.1 Closing the loop
- 5.2 GCO(s) control to output transfer function
- 5.3 Error amplifier compensation network
- 5.4 LED small signal model
- 5.5 Total loop gain
- 5.6 Compensation network design
- 5.7 Example of system design
- 5.8 Dimming operation
- 5.9 Component selection
- 5.10 Layout considerations
- 5.11 Thermal considerations
- 5.12 Short-circuit protection
- 5.13 Application circuit
- 6 Application notes - alternative topologies
- 7 Package mechanical data
- 8 Ordering information
- 9 Revision history

LED5000 Application notes - alternative topologies
Doc ID 023951 Rev 1 35/51
Since the maximum operating voltage of the LED5000 is 48 V, according to
Equation 51
the
maximum input voltage of the application is 48-18.7=29.3 V
The output voltage is given by:
Equation 52
where the ideal duty cycle D
IDEAL
for the buck-boost converter is:
Equation 53
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.
The peak current flowing in the embedded switch is:
Equation 54
while its average current level is equal to:
Equation 55
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.
The switch peak current must be lower than the minimum current limit of the overcurrent
protection (see
Section Table 5.: Electrical characteristics
for details) while the average
current must be lower than the rated DC current of the device.
As a consequence, the maximum output current is:
Equation 56
where I
SW MAX
represents the rated current of the device.
The current capability is reduced by the term (1-D
REAL
) and so, for example, with a duty
cycle of 0.5, and considering an average current through the switch of 3 A, the maximum
output current deliverable to the load is 1.5 A.
The
Figure 24
shows the schematic circuit for an LED current source based on inverting
buck-boost topology. The input voltage ranges from 10 to 26 V and it can drive a string
composed of 10 LEDs with1 A DC.
V
OUT
V
IN
–
D
IDEAL
1D
IDEAL
–
----------------------------
⋅=
D
IDEAL
V–
OUT
V
IN
V
OUT
–
------------------------------=
I
SW
I
LOAD
1D
REAL
–
---------------------------
I
RIPPLE
2
--------------------+
I
LOAD
1D
REAL
–
---------------------------
V
IN
2L⋅
-------------
D
f
SW
---------
⋅+==
I
SW
I
LOAD
1D
REAL
–
---------------------------=
I
LOAD MAX
I
SW MAX
1D
REAL
–()⋅≅