LM4924SDBD National Semiconductor, LM4924SDBD Datasheet - Page 15

• Manufacturer Part Number: LM4924SDBD
• Description: BOARD EVALUATION LM4924SD
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4924SDBD

• Amplifier Type: Class AB
• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 40mW x 2 @ 16 Ohm
• Voltage - Supply: 1.5 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4924
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

PCB LAYOUT GUIDELINES
This section provides practical guidelines for mixed signal
PCB layout that involves various digital/analog power and
ground traces. Designers should note that these are only
"rule-of-thumb" recommendations and the actual results will
depend heavily on the final layout.
Minimization of THD
PCB trace impedance on the power, ground, and all output
traces should be minimized to achieve optimal THD perfor-
mance. Therefore, use PCB traces that are as wide as pos-
sible for these connections. As the gain of the amplifier is
increased, the trace impedance will have an ever increasing
adverse affect on THD performance. At unity-gain (0dB) the
parasitic trace impedance effect on THD performance is re-
duced but still a negative factor in the THD performance of
the LM4924 in a given application.
GENERAL MIXED SIGNAL LAYOUT RECOMMENDATION
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 greatly en-
hance low level signal performance. Star trace routing refers
15
to using individual traces to feed power and ground to each
circuit or even device. This technique will 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 Connections
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. Further, 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 signal 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 cross talk.
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