ISL6730 Datasheet, PDF (13/19 Pages) Intersil Corporation – Reduce component size requirements

ISL6730A, ISL6730B, ISL6730C, ISL6730D
Table 3 shows the design parameters.
TABLE 3. CONVERTER DESIGN PARAMETERS
PARAMETER
CONDITIONS
MIN TYP MAX UNIT
VLINE
85 115 265 VAC
FLINE
47
63 Hz
P_OMAX
T_HOLD
Efficiency
Maximum Output Power
Hold Up Time
VLINE = 115VAC
92
300 W
20
ms
%
BOOST INDUCTOR SELECTION
First, calculate the maximum input RMS current, I_INMAX.
I_INMAX
=
--------^P----^O-----^M----^A----^X----------
η • V_RMSmin
(EQ. 7
Where η is the converter efficiency at V_RMSmin. PF is the power
factor at V_RMSmin.
I_INMAX = ₀----_.-₉--³--₂-⁰---⁰-_•---^W-₈---₅----_V-- = 3.84A
(EQ. 8)
Assuming the current is sinusoidal and the peak to peak ripple at
line is 40%.
The boost inductor, L_BST, is given by the following equation:
L_B
S
T
≥
--------------------²---^V-----^R----^M-----^S---^m-----ⁱ--ⁿ----------------
0.4 • F_sw • 2 • I_INMAX
•
⎛
⎜
⎝
1
–
-----²-----^•--_V--^V---_O-^R---_U-^M---_T--^S----^m-----ⁱ-ⁿ--_{⎠⎟⎞}
(EQ. 9)
L_B
S
T
≥
0^----.^--4^----•^-----6^---2^----k8^---H5^----V-z^-----•^----3^---.^--8^---4^----A^--
•
⎛
⎝
1
–
-----²-₃---₉-^•--₀--⁸--_V-⁵----^V--_⎠⎞
=
617 μ H
(EQ. 10)
The peak current of the inductor is the sum of the average peak
inductor current and half of the peak to peak ripple current.
Select and design the boost inductor as given by Equation 11.
The ISL6730A, ISL6730B, ISL6730C, ISL6730D provides peak
current limit function that can prevent the boost inductor
saturation. Assuming 25% margin is given to the OCP threshold,
select and design the boost inductor with saturation current
given by Equation 11 with 25% more.
I_LPeak =
2
•
I_INM
A
X
•
⎛
⎝
1
+
0_---2-._--4_{-⎠⎞}
(EQ. 11)
I_LPeak = 2 • 3.88A • _⎝⎛1 + ⁰---₂-^.--⁴-_⎠⎞ = 6.5A
INPUT RECTIFIER
The maximum average input current is calculated:
I_INAVE(max)
=
-²----^•---------²-----^•----^I--^I--^N----^M-----^A----^X-
π
(EQ. 12)
(EQ. 13)
I_INAVE(max)
=
-²----^•---------²-----^•----³---^.--⁸---⁸----^A--
π
=
3.5 A
(EQ. 14)
Select the bridge diode using Equation 15 and sufficient reverse
breakdown voltage. Assuming the forward voltage, V_F,BR, is 1V
across each rectifier diode. The power loss of the rectifier bridge
can be calculated:
P_BR = 2 • V_{F, BR} • I_INAVE(MAX)
(EQ. 15)
P_BR = 2 • 1V • 3.5A = 7W
(EQ. 16)
INPUT CAPACITOR SELECTION
Refer to Table 2 for the recommended input filter capacitor value.
C_F1
=
300 W
•
0_----._--3_---3_--
100
=
0.99 μ F
(EQ. 17)
This is the recommended capacitor used after the diode bridge.
For better power factor, less capacitance can be used. To lower
the input filter inductor size, more capacitance can be used.
Two 0.47µF capacitors in parallel are used for C_F1.
BOOST DIODE SELECTION
The boost diode loss is determined by the diode forward voltage
drop, V_F and the output average current. The maximum output
current is:
I_OUT(max)
=
P_{-----O----M-----A----X--}
V_OUT
(EQ. 18)
I_OUT(max)
=
3_----0_---0_----W_----
390 V
=
0.77 A
(EQ. 19)
The forward power loss on the diode is:
P_FD = I_OUT(max) • V_F
(EQ. 20)
P_FD = 0.77A • 1.85V = 1.42W
The IDD03E60 part is selected.
(EQ. 21)
The reverse recovery loss on the diode can be calculated. The
Q_RR is found from the diode datasheet. Q_RR = 220nC when
I_F = 3.5A.
The reverse recover loss on the diode can be estimated:
P_RRD
=
1_--
4
•
Q
R
R
•
V_O
U
T
•
F
s
w
P_RRD
=
1_--
4
•
220 n C
•
390 V
•
62 k H z
=
1.33 W
(EQ. 22)
(EQ. 23)
The total power loss on the diode is:
P_D = P_FD + P_RRD = (1.42 + 1.35)W = 2.75W
(EQ. 24)
MOSFET POWER DISSIPATION
The power dissipation on the MOSFET is from two different types
of losses; the condition loss and the switching loss.
For the MOSFET, the worst case is at minimum line input voltage.
First, the drain to source RMS current is calculated:
I_DS(max) = I_INMAX
1
–
8_{---3---π---}2_-
•
V_{-----R----M-----S----m----i--n-}
V_OUT
(EQ. 25)
I_DS(max) = 3.88A
1–
8_---------2_-
3π
•
--⁸---⁵----^V----
390 V
=
3.3 A
(EQ. 26)
13
FN8258.1
August 8, 2013