MAX8664 Maxim Integrated Products, MAX8664 Datasheet - Page 24

• Manufacturer Part Number: MAX8664
• Description: Step-Down Controller
• Manufacturer: Maxim Integrated Products

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The input filter capacitors reduce peak currents drawn
from the power source and reduce noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitors must meet the ripple current
requirement (I
The ripple current requirement can be estimated by the
following equation:
Choose a capacitor that exhibits less than 10°C tem-
perature rise at the maximum operating RMS current for
optimum long-term reliability.
Careful PCB layout is an important factor in achieving
low switching losses and clean, stable operation. The
switching power stage requires particular attention.
Follow these guidelines for good PCB layout:
1) A multilayer PCB is recommended.
2) Place IC decoupling capacitors as close as possi-
Low-Cost, Dual-Output, Step-Down
Controller with Fast Transient Response
24
I
RMS
ble to the IC pins. Keep separate power ground
and signal ground planes. Place the low-side
MOSFETs near the PGND pin. Arrange the high-
side MOSFETs and low-side MOSFETs in such a
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=
V
1
IN
(
I
OUT
1
)
RMS
2
Applications Information
×
V
OUT
) imposed by the switching currents.
1
×
(
V
IN
−
V
PCB Layout Guidelines
OUT
1
)
+
(
I
OUT
2
Input Capacitor
)
2
×
V
OUT
2
×
(
V
IN
−
V
OUT
2
)
3) Pour an analog ground plane in the second layer
4) Connect input, output, and VL capacitors to the
5) Place the MOSFETs as close as possible to the IC
6) Connect the drain leads of the power MOSFET to a
7) Place the feedback network components as close
8) The current-limit setting RC should be Kelvin con-
Refer to the MAX8664 evaluation kit for an example layout.
way that the high-side MOSFET’s drain is close and
near the low-side MOSFET’s source. This allows the
input ceramic decoupling capacitor to be placed
directly across and as close as possible to the
high-MOSFET’s drain and the low-side MOSFET’s
source. This helps contain the high switching cur-
rent within this small loop.
underneath the IC to minimize noise coupling.
power ground plane; connect all other capacitors to
the signal ground plane.
to minimize trace inductance of the gate drive loop.
If parallel MOSFETs are used, keep the trace
lengths to both gates equal and short.
large copper area to help cool the device. Refer to
the power MOSFET data sheet for recommended
copper area.
as possible to the IC pins.
nected to the high-side MOSFETs’ drain.