Texas Instruments LM3429 Evaluation Boards LM3429BSTEVAL/NOPB LM3429BSTEVAL/NOPB Datenbogen
Produktcode
LM3429BSTEVAL/NOPB
(1-D
MID
)
D
I
I
LED
RMS
CIN
x
x
=
-
MID
C
IN
=
'
V
IN-PP
x f
SW
I
LED
x D
C
IN
=
8 x
'
V
IN-PP
x f
SW
'
i
L-PP
C
IN
=
I
LED
x (1 - D) x D
'
V
IN-PP
x f
SW
x
=
0
U
T
T
-
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
1
Z
x
x
+
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
3
P
+
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
2
P
+
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
1
P
x
=
0
U
T
T
1
x
x
+
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
3
P
+
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
2
P
+
1
¸
¸
¹
¹
·
¨
¨
©
©
§
s
Z
1
P
1
=
C
FS
3
P
10
x
Z
max
3
P
=
Z
(
)
10
,
1
Z
1
P
x
Z
Z
1
CMP
C
=
6
2
P
e
5
x
Z
SNVS616G – APRIL 2009 – REVISED MAY 2013
(57)
If analog dimming is used, C
CMP
should be approximately 4x larger to maintain stability as the LEDs are dimmed
to zero.
A high frequency compensation pole (
ω
P3
) can be used to attenuate switching noise and provide better gain
margin. Assuming R
FS
= 10
Ω
, C
FS
is calculated according to the higher value of the pole and the RHP zero of
the system (shown as a maximizing function):
(58)
(59)
The total system loop gain (T) can then be written as:
Buck
(60)
Boost and Buck-boost
(61)
8. INPUT CAPACITANCE
Set the nominal input voltage ripple (
Δ
v
IN-PP
) by solving for the required capacitance (C
IN
):
Buck
(62)
Boost
(63)
Buck-boost
(64)
Use D
MAX
to set the worst case input voltage ripple, when solving for C
IN
in a buck-boost regulator and D
MID
= 0.5
when solving for C
IN
in a buck regulator.
The minimum allowable RMS input current rating (I
CIN-RMS
) can be approximated:
Buck
(65)
28
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