EVALED2000P STMicroelectronics, EVALED2000P Datasheet - Page 23

• Manufacturer Part Number: EVALED2000P
• Description: LED Lighting Development Tools LED2000 3A 850KHz 3.0V to 18V Eval BRD
• Manufacturer: STMicroelectronics

Specifications of EVALED2000P

• Product Category: LED Lighting Development Tools
• Rohs: yes
• Product: Evaluation Boards
• Operating Supply Voltage: 3 V to 18 V
• For Use With: LED2000

LED2000
Figure 15. Equivalent circuit
The LED ripple current can be calculated as the inductor ripple current ratio flowing into the
output impedance using the Laplace transform (see
Equation 23
where the term 8/
a triangular shape) and I
Equation 24
so L value can be calculated as:
Equation 25
where T
As a consequence, the lower the inductor value (so the higher the current ripple), the higher
the C
A general rule to dimension L value is:
Equation 26
Finally, the required output capacitor value can be calculated equalizing the LED current
ripple specification with the module of the Fourier transformer (see
at f
SW
L
------------
I
LED
=
I
OUT
L
frequency.
I
n
------------------------------------------------------------------------
L
OFF
LED
0.5
I
=
RIPPLE
value would be to meet the specification.
V
--------------- -
is the OFF-time of the embedded high switch, given by 1-D.
OUT
L
V
FW_LED
s
I
T
L
2
=
OFF
represents the main harmonic of the inductor current ripple (which has
----------------------------------------------------------------------------------------------------------------------- -
1
+
+
100mV
=
s
----- -
n
------------------------------------------------------------------------
8
L
2
LED
is the inductor current ripple.
R
S
Doc ID 023432 Rev 3
I
+
T
L
OFF
ESR
V
FW_LED
1
L
=
+
+
s
n
n
------------------------------------------------------------------------
LED
LED
+
ESR
100mV
R
V
LED
FW_LED
C
OUT
I
T
L
OFF
Figure
C
+
OUT
100mV
11):
1
–
Application information
n
------------------------------------------------------------------------
Equation
LED
V
FW_LED
V
23) calculated
IN
+
100mV
23/40