LM4674SQBD National Semiconductor, LM4674SQBD Datasheet - Page 14

• Manufacturer Part Number: LM4674SQBD
• Description: BOARD EVALUATION LM4674SQ
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4674SQBD

• Amplifier Type: Class D
• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 2.5W x 2 @ 4 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4674
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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PCB LAYOUT GUIDELINES
As output power increases, interconnect resistance (PCB
traces and wires) between the amplifier, load and power sup-
ply create a voltage drop. The voltage loss due to the traces
between the LM4674 and the load results in lower output
power and decreased efficiency. Higher trace resistance be-
tween the supply and the LM4674 has the same effect as a
poorly regulated supply, increasing ripple on the supply line,
and reducing peak output power. The effects of residual trace
resistance increases as output current increases due to high-
er output power, decreased load impedance or both. To main-
tain the highest output voltage swing and corresponding peak
output power, the PCB traces that connect the output pins to
the load and the supply pins to the power supply should be
as wide as possible to minimize trace resistance.
The use of power and ground planes will give the best THD
+N performance. In addition to reducing trace resistance, the
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use of power planes creates parasitic capacitors that help to
filter the power supply line.
The inductive nature of the transducer load can also result in
overshoot on one or both edges, clamped by the parasitic
diodes to GND and VDD in each case. From an EMI stand-
point, this is an aggressive waveform that can radiate or
conduct to other components in the system and cause inter-
ference. In is essential to keep the power and output traces
short and well shielded if possible. Use of ground planes
beads and micros-strip layout techniques are all useful in pre-
venting unwanted interference.
As the distance from the LM4674 and the speaker increases,
the amount of EMI radiation increases due to the output wires
or traces acting as antennas become more efficient with
length. Ferrite chip inductors places close to the LM4674 out-
puts may be needed to reduce EMI radiation.