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LM3421 Datasheet(PDF) 38 Page - Texas Instruments

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Part # LM3421
Description  N-Channel Controllers for Constant Current LED Drivers
PDF  65 Pages
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Manufacturer  TI1 [Texas Instruments]
Direct Link  http://www.ti.com
Logo TI1 - Texas Instruments

LM3421 Datasheet(HTML) 38 Page - Texas Instruments

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CT = 1 nF
RT = 49.9 k:
25
25
=
49.9 k: x 1 nF
fSW =
RT x CT
= 501 kHz
25
25
=
500 kHz x 1 nF
= 50 k:
RT =
fSW x CT
DMAX
=
=
677
.
0
=
V
21
V
10
V
21 +
V
O
V
V
IN-MIN
O +
21V
=
21V + 70V
= 0.231
DMIN =
VO + VIN-MAX
VO
533
.
0
467
.
0
1
D
1
'
D
=
-
=
-
=
D
=
=
467
.
0
=
V
21
V
24
V
21 +
V
O
V
V
IN
O +
:
=
:
x
=
x
=
95
.
1
m
325
6
r
N
r
LED
D
V
21
V
5
.
3
6
V
N
V
LED
O
=
x
=
x
=
LM3421, LM3421-Q1
LM3423, LM3423-Q1
SNVS574D – JULY 2008 – REVISED SEPTEMBER 2011
www.ti.com
VIN-MIN = 10V
VIN-MAX = 70V
fSW = 500 kHz
VSNS = 100 mV
ILED = 1A
ΔiL-PP = 700 mA
ΔiLED-PP = 12 mA
ΔvIN-PP = 100 mV
ILIM = 6A
VTURN-ON = 10V
VHYS = 3V
VTURN-OFF = 40V
VHYSO = 10V
1. OPERATING POINT
Solve for VO and rD:
(95)
(96)
Solve for D, D', DMAX, and DMIN:
(97)
(98)
(99)
(100)
2. SWITCHING FREQUENCY
Assume CT = 1 nF and solve for RT:
(101)
The closest standard resistor is 49.9 k
Ω therefore fSW is:
(102)
The chosen component from step 2 is:
(103)
3. AVERAGE LED CURRENT
Solve for RSNS:
38
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1



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