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| LM3409MY-NOPB Datasheet, PDF (25/43 Pages) Texas Instruments – PFET Buck Controller for High Power LED Drivers | |||
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LM3409, LM3409HV, LM3409-Q1
www.ti.com
ILED
=
5
VADJ
x RSNS
-
'iL- PP
2
ILED
=
5
1.24V
x 0.099:
-
1.027A
2
= 1.97A
The chosen component from step 3 is:
RSNS = 0.1:
SNVS602J â MARCH 2009 â REVISED MAY 2013
(54)
(55)
4. OUTPUT CAPACITANCE
No output capacitance is necessary.
5. INPUT CAPACITANCE
Determine tON:
tON =
1
fSW
-
t OFF
=
1
528 kHz
-
440 ns =1.45Ps
(56)
Solve for CIN-MIN:
CIN - MIN
=
ILED x
'vIN -
tON
PP
=
1.97A x 1.45Ps
1.44V
=
1.98
PF
(57)
Choose CIN:
CIN = CIN- MIN x 2 = 3.96 PF
(58)
Determine IIN-RMS:
IIN-RMS = ILED x fSW x tON x t OFF
IIN-RMS = 1.97A x 528 kHz x 1.45 Ps x 440 ns = 831 mA
(59)
The chosen components from step 5 are:
CIN1 = CIN2 = 2.2 PF
(60)
6. PFET
Determine minimum Q1 voltage rating and current rating:
VT-MAX = VIN-MAX = 75V
(61)
IT
=
D
x
ILED
=
VO x ILED
VIN x K
=
35V x1.97A
48V x 0.95
= 1.51A
(62)
A 100V, 3.8A PFET is chosen with RDS-ON = 190m⦠and Qg = 20nC. Determine IT-RMS and PT:
IT-RMS = ILED x
D
x
¨¨¨©§1+
1
12
x
¨¨©§
'iL-PP
ILED
¸¸¹·2
¸·
¸¸¹
IT-RMS = 1.97A x
35V
48V x 0.95
x
¨¨©§1+
1
12
x
¨¨©§11.0.9277AA ¸¸¹·2¸¸¹·
IT-RMS = 1.74A
PT
=
IT-
2
RMS
x
RDSON
=
1.74
A2
x
190
m:
=
577
mW
Copyright © 2009â2013, Texas Instruments Incorporated
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Product Folder Links: LM3409 LM3409HV LM3409-Q1
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