ACT4501
Rev 2, 14-Nov-12
STABILITY COMPENSATION CONT’D
feedback resistance values for cable compensation.
R
FB1
is the high side resistor of voltage divider.
In the case of high R
FB1
used, the frequency
compensation
needs
to
be
adjusted
correspondingly. As show in Figure 6, adding a
capacitor in paralled with R
FB1
or increasing the
compensation capacitance at COMP pin helps the
system stability.
Figure 5:
Cable Compensation at Various Resistor Divider
Values
Delta Output Voltage vs. Output Current
ACT4501-003
0.3
V
IN
= 12V
V
0UT
= 5V
=3
1
B1
2)
Place input decoupling ceramic capacitor C
IN
as
close to IN pin as possible. C
IN
is connected
power GND with vias or short and wide path.
3)
Return FB, COMP and ISET to signal GND pin,
and connect the signal GND to power GND at a
single point for best noise immunity.
4)
Use copper plane for power GND for best heat
dissipation and noise immunity.
5)
Place feedback resistor close to FB pin.
6) Use short trace
connecting
HSB-C
HSB
-SW loop
Figure 7 shows an example of PCB layout.
Delta Output Voltage (V)
0.25
R
F
00
k
B
0.2
R
F
R
FB
=2
70
k
k
=2
1
40
0.15
1
R
FB
=2
00k
0.1
R
FB1
0k
= 15
100k
0.05
0
0
200
400
600
R
FB1
=
k
R
FB1
= 51
800
1000
Output Current (mA)
Figure 6:
Frequency Compensation for High R
FB1
Figure 7: PCB Layout
Figure 8 gives one typical car charger application
schematics and associated BOM list.
PC Board Layout Guidance
When laying out the printed circuit board, the
following checklist should be used to ensure proper
operation of the IC.
1) Arrange the power components to reduce the
AC loop size consisting of C
IN
, IN pin, SW pin
and the schottky diode.
Innovative Power
TM
-9-
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ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
