Texas Instruments LM3448 Evaluation Board LM3448-EDSNEV/NOPB LM3448-EDSNEV/NOPB 데이터 시트
제품 코드
LM3448-EDSNEV/NOPB
dv
i
C
dt
1
2 5 .2 V
2 .5 2 V
1-
0 .8
1 1 5
2 V
L 2
6 7 7 H
2 5 0 k H z
0 .1 2 A
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u
¨
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¹
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¹
P
u
O F F
L E D
t
V
C 1 1
1 7 5 p F
R 4
1 . 2 7 6 V
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¹
L E D
C O L L
V
R 4
3 6 0 k
I
:
O N ( M IN )
1
2 5 . 2 V
0 . 8
1 3 5
2 V
t
3 . 2 3 s
6 3 8 n s
1
2 5 . 2 V
1-
0 . 8
1 3 5
2 V
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·
u
¨
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¹
u
P
§
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u
¨
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¹
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O F F
1
2 5 . 2 V
1-
0 . 8
1 1 5
2 V
t
3 . 2 3 s
2 5 0 k H z
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u
¨
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P
B U C K ( M A X )
V
1 3 5
2
1 9 0 V
SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013
2. Calculate maximum voltage V
BUCK
voltage,
(39)
3. Calculate t
OFF
at V
BUCK
nominal line voltage,
(40)
4. Calculate t
ON(MIN)
at high line to ensure that
–
t
ON(MIN)
> 200ns,
(41)
5. Calculate C11 and R4:
6. Choose current through R4 (between 50µA and 100µA): 70µA
–
Calculate R4,
(42)
7. Choose a standard value of 365k
Ω
8. Calculate C11,
(43)
9. Choose standard value of 120pF.
10. Calculate inductor value at t
OFF
= 3µs,
(44)
11. Choose C10 = 1.0µF, 200V.
12. Calculate valley-fill capacitor values,
–
VAC low line = 90VAC, V
BUCK
minimum equals 45V (no TRIAC dimming at maximum LED current). Set
droop for 20V maximum at full load and low line.
(45)
–
Since "i" equals P
OUT
/V
BUCK
= 224mA, "dV" equals 20V, "dt" equals 2.78ms, and then C
TOTAL
equals
31µF.
–
Therefore choose C7 = C9 = 15µF.
Copyright © 2011–2013, Texas Instruments Incorporated
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