LM48510_0710 NSC [National Semiconductor], LM48510_0710 Datasheet - Page 13

• Manufacturer Part Number: LM48510_0710
• Description: Boosted Class D Audio Power Amplifier
• Manufacturer: NSC [National Semiconductor]

FET on resistance increases at V
the internal N-FET has less gate voltage in this input voltage
range (see Typical Performance Characteristics curves).
Above V
5V.
The maximum peak switch current the device can deliver is
dependent on duty cycle. For higher duty cycles, see Typical
Performance Characteristics curves.
INDUCTOR SUPPLIERS
Recommended suppliers of inductors for the LM48510 in-
clude, but are not limited to Taiyo-Yuden, Sumida, Coilcraft,
Panasonic, TDK and Murata. When selecting an inductor,
make certain that the continuous current rating is high enough
to avoid saturation at peak currents. A suitable core type must
be used to minimize core (switching) losses, and wire power
losses must be considered when selecting the current rating.
PCB LAYOUT GUIDELINES
High frequency boost converters require very careful layout
of components in order to get stable operation and low noise.
All components must be as close as possible to the LM48510
device. It is recommended that a four layer PCB be used so
that internal ground planes are available.
Some additional guidelines to be observed:
1. Keep the path between L1, D1, and Co extremely short.
Parasitic trace inductance in series with D1 and Co will in-
crease noise and ringing.
2. The feedback components R1, R2 and C
close to the FB pin to prevent noise injection on the FB pin
trace.
3. If internal ground planes are available (recommended) use
vias to connect directly to ground at pin 2 of U1, as well as the
negative sides of capacitors C
GENERAL MIXED-SIGNAL LAYOUT RECOMMENDATION
This section provides practical guidelines for mixed signal
PCB layout that involves various digital/analog power and
IN
= 5V, the FET gate voltage is internally clamped to
s
1 and Co.
IN
values below 5V, since
f1
must be kept
13
ground traces. Designers should note that these are only
"rule-of-thumb" recommendations and the actual results will
depend heavily on the final layout.
Power and Ground Circuits
For two layer mixed signal design, it is important to isolate the
digital power and ground trace paths from the analog power
and ground trace paths. Star trace routing techniques (bring-
ing individual traces back to a central point rather than daisy
chaining traces together in a serial manner) can have a major
impact on low level signal performance. Star trace routing
refers to using individual traces to feed power and ground to
each circuit or even device. This technique will take require a
greater amount of design time but will not increase the final
price of the board. The only extra parts required may be some
jumpers.
Single-Point Power / Ground Connection
The analog power traces should be connected to the digital
traces through a single point (link). A "Pi-filter" can be helpful
in minimizing high frequency noise coupling between the ana-
log and digital sections. It is further recommended to place
digital and analog power traces over the corresponding digital
and analog ground traces to minimize noise coupling.
Placement of Digital and Analog Components
All digital components and high-speed digital signals traces
should be located as far away as possible from analog com-
ponents and circuit traces.
Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces par-
allel to each other (side-by-side) on the same PCB layer.
When traces must cross over each other do it at 90 degrees.
Running digital and analog traces at 90 degrees to each other
from the top to the bottom side as much as possible will min-
imize capacitive noise coupling and crosstalk.
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