ACT4515
Rev 6, 14-Nov-12
STABILITY COMPENSATION CONT’D
simple, user-programmable cable voltage drop
compensation using the impedance at the FB pin.
Use the curve in Figure 5 to choose the proper
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 7, adding a
capacitor in paralled with R
FB1
or increasing the
compensation capacitance at COMP pin helps the
system stability.
Figure 6:
Cable Compensation at Various Resistor Divider
Values
Delta Output Voltage vs. Output Current
0.64
ACT4515-003
0.56
0.48
0.4
0.32
0.24
0.16
0.08
0
0
250
500
750
1000
V
IN
= 14V
V
0UT
= 5V
I
ISET
= 1.5A
R
F
k
40
k
and the schottky diode.
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
7) Reduce SW Pad Size
Figure 8 shows an example of PCB layout.
Delta Output Voltage (V)
B
=3
1
R
F
B
00
=2
1
R
FB
=2
1
00
k
1
R
FB
=1
50k
R
FB1
= 10
0k
R
FB1
=
68k
k
R
FB1
= 12
1250
1500
Output Current (mA)
Figure 7:
Frequency Compensation for High R
FB1
Figure 8: PCB Layout
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
Innovative Power
TM
-9-
Figure 9 and Figure 10 give two typical car charger
application schematics and associated BOM list.
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