Datasheet

OUT IN_MIN
PEAK _ LOW _LINE
OUT
V V 2
390 V 85 V 2
D 0.69
V 390 V
-
-
= = »
2
2
IN _MIN PEAK _ LOW _LINE
OUT MIN
V D
0.92(85 V) 0.69
L1 L2 340 H
P f 300 W 45kHz
h´ ´
= = = » m
´ ´
OUT
LPEAK
IN _MIN
P 2
300 W 2
I 5.4 Apk
V 85 V 0.92
= = »
´ h ´
LPEAK
LRMS
I
5.4 A
I 2.2 Arms
6 6
= = »
OUT IN_MAX
P
s
V - V 2
N
390 V - 265 V 2
8
N 2 V 2 V
= = »
OUT S
ZA ZB
P
V N
390 V
R R 16.3k
N 3mA 8 3mA
= ³ = » W
´ ´
ZA ZB
R R 20k= = W
UCC28063
www.ti.com SLUSAO7 –SEPTEMBER 2011
Inductor Selection
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 18.
(18)
The minimum switching frequency of the converter (f
MIN
) under low line conditions 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
is set to 45 kHz. For
a 2-phase interleaved design, L1 and L2 are determined as shown in Equation 19.
(19)
The inductor for this design would have a peak current (I
LPEAK
) of 5.4 A, as shown in Equation 20, and an RMS
current (I
LRMS
) of 2.2 A, as shown in Equation 21.
(20)
(21)
This converter uses constant on time (T
ON
) and zero-current detection (ZCD) to set up the converter timing.
Auxiliary windings on L1 and L2 detect when the inductor currents are zero. Selecting the turns ratio using
Equation 22 ensures that there will be at least 2 V at the peak of high line to reset the ZCD comparator after
every switching cycle.
The turns-ratio of each auxiliary winding is:
(22)
ZCD Resistor Selection (R
ZA
, R
ZB
)
The minimum value of the ZCD resistors is selected based on the internal clamps maximum current ratings of 3
mA, as shown in Equation 23.
(23)
In this design the ZCD resistors are set to 20 kΩ, as shown in Equation 24.
(24)
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