LM4991LD/NOPB National Semiconductor, LM4991LD/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM4991LD/NOPB
• Description: IC AMP AUDIO PWR 3W MONO AB 8LLP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4991LD/NOPB

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 3W x 1 @ 3 Ohm
• Voltage - Supply: 2.2 V ~ 5.5 V
• Features: Depop, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 8-LLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM4991LD/NOPB; LM4991LD

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Typical Performance Characteristics
Application Information
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATION
The LM4991’s exposed-DAP (die attach paddle) package
(LD) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. This
allows rapid heat transfer from the die to the surrounding
PCB copper traces, ground plane, and surrounding air. The
result is a low voltage audio power amplifier that produces
2W at ≤ 1% THD with a 4Ω load. This high power is achieved
through careful consideration of necessary thermal design.
Failing to optimize thermal design may compromise the
LM4991’s high power performance and activate unwanted,
though necessary, thermal shutdown protection.
The LD package must have its DAP soldered to a copper
pad on the PCB. The DAP’s PCB copper pad is connected to
a large plane of continuous unbroken copper. This plane
forms a thermal mass, heat sink, and radiation area. Place
the heat sink area on either outside plane in the case of a
Supply Voltage, R
Frequency Response vs
Input Capacitor Size
Output Power vs
L
= 16Ω
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two-sided PCB, or on an inner layer of a board with more
than two layers. Connect the DAP copper pad to the inner
layer or backside copper heat sink area with 4(2x2) vias. The
via diameter should be 0.012in-0.013in with a 1.27mm pitch.
Ensure efficient thermal conductivity by plating through the
vias.
Best thermal performance is achieved with the largest prac-
tical heat sink area. If the heatsink and amplifier share the
same PCB layer, a nominal 2.5in
operation with a 4Ω load. Heatsink areas not placed on the
same PCB layer as the LM4991 should be 5in
same supply voltage and load resistance. The last two area
recommendations apply for 25˚C ambient temperature. In-
crease the area to compensate for ambient temperatures
above 25˚C. The LM4991’s power de-rating curve in the
Typical Performance Characteristics shows the maximum
power dissipation versus temperature. An example PCB lay-
out for the LD package is shown in the Demonstration
Board Layout section. Further detailed and specific infor-
mation concerning PCB layout, fabrication, and mounting an
Supply Voltage, R
Output Power vs
2
L
area is necessary for 5V
= 32Ω
2
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(min) for the