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LM3421 Datasheet(PDF) 34 Page - Texas Instruments

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Part # LM3421
Description  N-Channel Controllers for Constant-Current LED Drivers
PDF  72 Pages
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Manufacturer  TI1 [Texas Instruments]
Direct Link  http://www.ti.com
Logo TI1 - Texas Instruments

LM3421 Datasheet(HTML) 34 Page - Texas Instruments

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IL-RMS =
1 +
1
12
x
ILED
'IL-PP x D'
¸
¹
·
¨
©
§
2
D'
ILED
x
IL-RMS = ILED x
1 +
1
12
x
ILED
'IL-PP
¸
¹
·
¨
©
§
2
IN
L PP
SW
V
D
L1
i
f
K


K
IN
O
L PP
SW
(V
V ) D
L1
i
f
K


K
1.24V
R
HSP =
R
R
I
SNS
CSH
LED
x
x
SNS
R
=
SNS
V
LED
I
T
25
R =
T
SW
C
f
x
(
)
T
25
R =
2
O
O
IN
V
V
V
-
x
x
2
IN
T
SW
V
C
f
x
x
RT =
25 x VIN - VO
fSW x CT X VIN
(
)
LM3421, LM3421-Q1, LM3423, LM3423-Q1
SNVS574F – JULY 2008 – REVISED JULY 2015
www.ti.com
Typical Applications (continued)
(39)
Buck (Constant Ripple vs. VO)
(40)
Boost and Buck-Boost
(41)
8.2.1.2.3
Average LED Current
For all topologies, set the average LED current (ILED) knowing the desired current sense voltage (VSNS) and
solving for RSNS:
(42)
If the calculated RSNS is too far from a desired standard value, then VSNS will have to be adjusted to obtain a
standard value.
Setup the suggested signal current of 100 µA by assuming RCSH = 12.4 kΩ and solving for RHSP:
(43)
If the calculated RHSP is too far from a desired standard value, then RCSH can be adjusted to obtain a standard
value.
8.2.1.2.4
Inductor Ripple Current
Set the nominal inductor ripple current (
ΔiL-PP) by solving for the appropriate inductor (L1):
Buck
(44)
Boost and Buck-Boost
(45)
To set the worst case inductor ripple current, use VIN-MAX and DMIN when solving for L1.
The minimum allowable inductor RMS current rating (IL-RMS) can be calculated as:
Buck
(46)
Boost and Buck-Boost
(47)
34
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Copyright © 2008–2015, Texas Instruments Incorporated
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1



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