Datasheet

dv
i = C
dt
25.2V
115
(350 kHz x 0.1A)
L2 =
2
= 580 PH
25.2V
1 
0.8
1
u
C11 =
t
OFF
1.276
V
LED
R4
= 175 pF
V
LED
R4 =
= 360 k:
I
COLL
25.2V
135
2
u 3.23 Ps = 638 ns
0.8
1
u
t
ON (MIN)
=
25.2V
135
2
1 
0.8
1
u
25.2V
115
(250 kHz)
2
= 3.23 Ps
1 
0.8
1
u
t
OFF
=
V
BUCK(MAX)
= 135
2
= 190V
LM3444
SNVS682C –NOVEMBER 2010–REVISED MAY 2013 www.ti.com
(36)
3. Calculate t
OFF
at V
BUCK
nominal line voltage:
(37)
4. Calculate t
ON(MIN)
at high line to ensure that t
ON(MIN)
> 200 ns:
(38)
5. Calculate C11 and R4:
6. Choose current through R4: (between 50 µA and 100 µA) 70 µA
(39)
7. Use a standard value of 365 kΩ
8. Calculate C11:
(40)
9. Use standard value of 120 pF
10. Calculate ripple current: 400 mA X 0.30 = 120 mA
11. Calculate inductor value at t
OFF
= 3 µs:
(41)
12. Choose C10: 1.0 µF 200V
13. Calculate valley-fill capacitor values:
V
AC
low line = 90V
AC
, V
BUCK
minimum equals 60V. Set droop for 20V maximum at full load and low line.
(42)
i equals P
OUT
/V
BUCK
(270 mA), dV equals 20V,
dt equals 2.77 ms, and
then C
TOTAL
equals 37 µF.
Therefore, C7 = C9 = 22 µF
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