ISL6745UEVAL2Z Intersil, ISL6745UEVAL2Z Datasheet - Page 3

• Manufacturer Part Number: ISL6745UEVAL2Z
• Description: EVAL BOARD 2 FOR ISL6745
• Manufacturer: Intersil

Specifications of ISL6745UEVAL2Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

There are three stages of operations:
During each switching period, the following circuit equations
can be derived.
SWITCH S1 TURNS ON
At the beginning of the cycle, when switch S1 turns on, the
free-wheeling current in L
the input inductor L
I
Since the voltage across C
applied to L
where 0 denote the initial condition of the state variables.
The switch current is the sum of the two inductor currents,
and is given in Equation 3. This stage ends at t
DIODE D5 CONDUCTS
The voltage applied to inductor L
inductor L
Equation 4. The current in L
stage ends when i
sum of both the inductor currents. The currents are given in
Equation 5, where t
DIODE D5 AND SWITCH S1 BLOCKING
This is the freewheeling period of both inductors L
The freewheeling currents are given in Equation 6.
i
i
i
i
i
i
L1
L1
L2
Q
L1
L2
D
1. The switch turns on, Diode is off.
2. The switch turns off, the diode is on.
3. Both switch and diode are off.
t ( )
t ( )
(0). The voltage applied to the input inductor L
t ( )
t ( )
t ( )
t ( )
=
=
=
=
=
=
(
i
NAME
L1(t)
i
–
⎛
⎜
⎝
⎛
⎜
⎝
v
L1(0)
I
i
i
CS
C1
C
ADJ
D
L1(0)
L1(0)
TABLE 1. SEPIC CONVERTER (Continued)
i
2
L1(0)
F
5
. The current in L
2
t
+
ON
. The inductor currents are given in Equation 2,
+
i
L2(t)
+
+
+
v
--------- - t
–
L
v
--------- - t
v
--------- - t
C1
v
--------- - t
L
L
1
V
C1
C1
L
C1
L1
1
1
2
O
1
=
ON
t
is V
ON
ON
equals -i
)
⎛
⎜
⎝
⎛
⎝
Feedback Capacitor
Brightness Dimming Control
The MOSFET Current
Output Diode
v
--------- -
----- -
L
is the interval when the switch is on.
L
1
C1
–
–
1
C1
1
⎛
⎜
⎝
v
------ - t
+
1
L
v
------ -
. The freewheeling current in L
L
O
2
+
1
----- -
L
is I
O
1
1
1
2
equals V
v
--------- -
2
⎞
⎟
⎠
⎞
⎟
⎠
L
C1
L2
⎞
⎠
decays according to
decays and reverses. This
t
3
L1
2
⎞
⎟
⎠
. The diode current is the
⎞
⎟
⎠
(0) and the voltage across
1
t
DESCRIPTION
is –V
C1
, the same voltage is
o
, the same as
ON
1
Application Note 1411
.
1
is V
and L
(EQ. 3)
(EQ. 2)
(EQ. 5)
(EQ. 4)
C1
.
1
2
is
.
where, the diode conducting time, t
volt-second balance of the inductors, where V
amplitude of the AC line voltage.
To ensure the converter operates in DCM, the freewheeling
time should be greater than or equal to zero as expressed in
Equation 8.
Therefore, the duty ratio of the PWM is expressed in
Equation 9.
Averaging this diode current in one switching cycle gives the
average output current I
Averaging the I
current of the output, since the average output capacitor
current is zero. Therefore, the output current equals the
average diode current. The output current also equals the
average current in inductor L
C
the line frequency as expressed in Equation 11.
The constraints for selecting the inductors are expressed in
Equation 12:
As can be seen, the maximum ripple current in the input
inductor L
expressed in Equation 13.
Since, we assume unity power factor, and assume the power
conversion efficiency is η as shown in Equation 14.
i
i
t
t
d
i
i
L
I
1
-- - V
2
L1
L2
O
O
d
s
1rp
1
2
<
≥
t ( )
=
||
1 ( )
1 ( )
1
=
is zero. Therefore, the dominate ripple frequency is twice
------------------- -
V
t
L
I
ON
=
1
t
--------- - V
O
----
t
V
V
=
2
1
ON
η
1
=
=
O
+
O
<
t
-----------------
∫
ON
--- - t
t
+
1
t
0
=
s
V
1
⎛
⎜
⎝
⎛
⎜
⎝
⎛
⎜
⎝
L
t
---------------------
V
i
i
l
I
l
d
∫
1
1
L1(0)
L1(0)
V
O
V
t
0
O
sin
s
occurs at the peaks of the input voltages as
O
1
t ( )dt
V
i
+
D
I
1
O
ω
V
t ( )dt
+
+
O
l
1
t
(t) over one line period, yields the average
=
⎞ 2 t
⎟
⎠
v
--------- - t
v
--------- - t
L
L
C1
C1
----------------- -
L
1
2
=
------------ -
1
s
4I
1
ON
ON
----------------- -
L
||
V
O
1
L
O
1
2
||
O
–
–
d
----------------------
L
(t) during that switching cycle.
v
------ - t
v
------ - t
L
L
2
2
4V
O
O
1
1
t
(
--------------------------------------------- -
s
t
2
ON
V
d
d
O
, since the average current in
⎞
⎟
⎠
⎞
⎟
⎠
1
2
V
2t
1
s
sin
d
V
, is determined by the
O
(
ω
1
t
)
)
2
l
is the
June 9, 2009
(EQ. 12)
(EQ. 13)
(EQ. 14)
(EQ. 10)
(EQ. 11)
AN1411.3
(EQ. 6)
(EQ. 9)
(EQ. 7)
(EQ. 8)