ACT4513
Active- Semi
Rev 6, 29-Jul-11
APPLICATIONS INFORMATION
CC Current Line Compensation
Output Voltage Setting
When operating at constant current mode, the
current limit increase slightly with input voltage. For
wide input voltage applications, a resistor RC is
added to compensate line change and keep output
high CC accuracy, as shown in Figure 3.
Figure 1:
Output Voltage Setting
Figure 3:
Iutput Line Compensation
VIN
IN
ACT4513
ISET
Rc
Figure 1 shows the connections for setting the
output voltage. Select the proper ratio of the two
feedback resistors RFB1 and RFB2 based on the
output voltage. Typically, use RFB2 ≈ 10kꢀ and
determine RFB1 from the following equation:
RISET
VOUT
⎛
⎜
⎞
⎟
RFB1 = RFB2
−1
Inductor Selection
(1)
0.808V
⎝
⎠
The inductor maintains a continuous current to the
output load. This inductor current has a ripple that is
dependent on the inductance value:
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.
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:
_
V
OUT × V VOUT
IN
(2)
L =
Figure 2:
VINfSWILOADMAXKRIPPLE
Curve for Programming Output CC Current
where VIN is the input voltage, VOUT is the output
voltage, fSW is the switching frequency, ILOADMAX is
the maximum load current, and KRIPPLE is the ripple
Output Current vs. RISET
factor. Typically, choose KRIPPLE
=
30% to
2400
correspond to the peak-to-peak ripple current being
30% of the maximum load current.
2000
1600
1200
800
400
0
With a selected inductor value the peak-to-peak
inductor current is estimated as:
_
VOUT × VIN VOUT
ILPK _
=
(3)
PK
L×VIN ×fSW
The peak inductor current is estimated as:
0
10
20
30
40
50
60
70
80 90
1
(4)
RISET (kꢀ)
ILPK =ILOADMAX
+
ILPK_
PK
2
Innovative PowerTM
- 6 -
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