Datasheet

+
-
RG1
CA
CP
CZ
RA
RZ
U1
VCC
RP
CB
RZA
RG2
RS
R
CF1
CF2
RB
CF4
RT
CF3
RD
RC
RZB
RF
RE
V
OUT
V
OUT
V
OUT
Inductor Selection
D =
PEAK_LOW_LINE
V V- Ö
OUT IN_MIN
2
V
OUT
» 0.69
=
390V 85V- Ö2
390V
(9)
L1=L2=
h ´ V xD
IN_MIN PEAK_LOW_LINE
2
P f
OUT MIN
´
» m340 H
=
0.92(85V) 0.69
2
300W 45kHz´
(10)
UCC28060
www.ti.com .................................................................................................................................................... SLUS767E – MAY 2007 – REVISED NOVEMBER 2008
Figure 31. Recommended PCB Layout
The boost inductor is selected based on the inductor ripple current requirements at the peak of low line.
Selecting the inductor requires calculating the boost converter duty cycle at the peak of low line (D
PEAK_LOW_LINE
),
as shown in Equation 9 .
The minimum switching frequency of the converter (f
MIN
) occurs at the peak of low line and is set between 25
kHz and 50 kHz to avoid audible noise. For this design example, f
MIN
was set to 45 kHz:
The inductor for this design would have a peak current (I
LPEAK
) of 5.4 A, as shown in Equation 11 , and an RMS
current (I
LRMS
) of 2.2 A, as shown in Equation 12 .
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