Texas Instruments LM3429 Evaluation Boards LM3429BSTEVAL/NOPB LM3429BSTEVAL/NOPB Scheda Tecnica
Codici prodotto
LM3429BSTEVAL/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
SNVS616G – APRIL 2009 – REVISED MAY 2013
Boost and Buck-boost
(40)
5. LED RIPPLE CURRENT
Set the nominal LED ripple current (
Δ
i
LED-PP
), by solving for the output capacitance (C
O
):
Buck
(41)
Boost and Buck-boost
(42)
To set the worst case LED ripple current, use D
MAX
when solving for C
O
.
The minimum allowable RMS output capacitor current rating (I
CO-RMS
) can be approximated:
Buck
(43)
Boost and Buck-boost
(44)
6. PEAK CURRENT LIMIT
Set the peak current limit (I
LIM
) by solving for the transistor path sense resistor (R
LIM
):
(45)
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
(46)
26
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