Texas Instruments LM3423 Evaluation Board LM3423BBLSCSEV/NOPB LM3423BBLSCSEV/NOPB Fiche De Données
Codes de produits
LM3423BBLSCSEV/NOPB
x
=
¨
¨
©
©
§
+
s
1
Z
1
P
¸
¸
¹
¹
·
0
U
T
U
T
1
LIM
R
=
LIM
I
245 mV
1-D
MAX
D
MAX
I
CO-RMS
= I
LED
x
I
RMS
CO
=
-
12
PP
-
LED
i
ü
O
C =
SW
PP
-
LED
D
f
ü
i
r
x
x
LED
D
I
x
O
C =
PP
L
i
-
'
PP
LED
D
SW
i
r
f
8
-
'
x
x
x
I
L-RMS
=
1 +
1
12
x
I
LED
'
I
L-PP
x D'
¸
¹
·
¨
©
§
2
D'
I
LED
x
SNVS574E – JULY 2008 – REVISED MAY 2013
Boost and Buck-boost
(47)
5. LED RIPPLE CURRENT
Set the nominal LED ripple current (
Δ
i
LED-PP
), by solving for the output capacitance (C
O
):
Buck
(48)
Boost and Buck-boost
(49)
To set the worst case LED ripple current, use D
MAX
when solving for C
O
. Remember, when PWM dimming it is
recommended to use a minimum of 40 µF of output capacitance to improve performance.
The minimum allowable RMS output capacitor current rating (I
CO-RMS
) can be approximated:
Buck
(50)
Boost and Buck-boost
(51)
6. PEAK CURRENT LIMIT
Set the peak current limit (I
LIM
) by solving for the transistor path sense resistor (R
LIM
):
(52)
7. LOOP COMPENSATION
Using a simple first order peak current mode control model, neglecting any output capacitor ESR dynamics, the
necessary loop compensation can be determined.
necessary loop compensation can be determined.
First, the uncompensated loop gain (T
U
) of the regulator can be approximated:
Buck
(53)
Copyright © 2008–2013, Texas Instruments Incorporated
33
Product Folder Links: