Datasheet
DocID023432 Rev 4 17/40
LED2000 Application notes
40
As a consequence, the LED equivalent circuit gives the
LED
(s) term correlating the output
voltage with the high impedance FB input:
Equation 14
6.5 Total loop gain
In summary, the open loop gain can be expressed as:
Equation 15
Example 1
Design specification:
V
IN
= 12 V, V
FW_LED
= 3.5 V, n
LED
= 2, r
LED
= 1.1 , I
LED
= 700 mA, I
LED RIPPLE
= 2%
The inductor and capacitor value are dimensioned in order to meet the I
LED RIPPLE
specification (see Section 7.1.2 for output capacitor and inductor selection guidelines):
L = 10
H, C
OUT
= 2.2
F MLCC (negligible ESR)
Accordingly, with Section 7.1.1 the sensing resistor value is:
Equation 16
Equation 17
The gain and phase margin Bode diagrams are plotted respectively in Figure 9 and
Figure 10.
LED
n
LED
R
SENSE
n
LED
r
LED
R
SENSE
+
--------------------------------------------------------- -=
Gs G
CO
sA
0
s
LED
n
LED
=
R
S
100 mV
700 mA
-------------------- - 140 m=
LED
n
LED
R
SENSE
n
LED
r
LED
R
SENSE
+
--------------------------------------------------------- -=
140 m
21,1 140 m+
------------------------------------------------- 0,06==