ACT4513
Rev 7, 14-Nov-12
APPLICATIONS INFORMATION
Output Voltage Setting
Figure 1:
Output Voltage Setting
CC Current Line Compensation
When operating at constant current mode, the
current limit increase slightly with input voltage. For
wide input voltage applications, a resistor R
C
is
added to compensate line change and keep output
high CC accuracy, as shown in Figure 3.
Figure 3:
Iutput Line Compensation
V
IN
R
c
IN
ACT4513
ISET
R
ISET
Figure 1 shows the connections for setting
output voltage. Select the proper ratio of the
feedback resistors R
FB1
and R
FB2
based on
output voltage. Typically, use R
FB2
≈
10kΩ
determine R
FB1
from the following equation:
⎛
V
⎞
R
FB1
=
R
FB 2
⎜
OUT
−
1
⎟
⎝
0 .808 V
⎠
the
two
the
and
(1)
Inductor Selection
The inductor maintains a continuous current to the
output load. This inductor current has a ripple that is
dependent on the inductance value:
Higher inductance reduces the peak-to-peak ripple
current. The trade off for high inductance value is
the increase in inductor core size and series
resistance, and the reduction in current handling
capability. In general, select an inductance value L
based on ripple current requirement:
CC Current Setting
ACT4513 constant current value is set by a resistor
connected between the ISET pin and GND. The CC
output current is linearly proportional to the current
flowing out of the ISET pin. The voltage at ISET is
roughly 1V and the current gain from ISET to output
is roughly 25000 (25mA/1µA). To determine the
proper resistor for a desired current, please refer to
Figure 2 below.
Figure 2:
Curve for Programming Output CC Current
V
OUT
×
(
V
IN
_
V
OUT
)
L
=
V
IN
f
SW
I
LOADMAX
K
RIPPLE
(2)
Output Current vs. R
ISET
ACT4513-002
2400
2000
Output Current (mA)
where V
IN
is the input voltage, V
OUT
is the output
voltage, f
SW
is the switching frequency, I
LOADMAX
is
the maximum load current, and K
RIPPLE
is the ripple
factor. Typically, choose K
RIPPLE
= 30% to
correspond to the peak-to-peak ripple current being
30% of the maximum load current.
With a selected inductor value the peak-to-peak
inductor current is estimated as:
I
LPK
_
PK
V
OUT
×
(
V
IN
_
V
OUT
)
=
L
×
V
IN
×
f
SW
1600
1200
800
400
(3)
The peak inductor current is estimated as:
0
0
10
20
30
40
50
60
70
80
90
R
ISET
(kΩ)
1
I
LPK
=
I
LOADMAX
+
I
LPK
_
PK
2
(4)
Innovative Power
TM
-6-
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