LM4856LQX/NOPB National Semiconductor, LM4856LQX/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM4856LQX/NOPB
• Manufacturer: National Semiconductor

Specifications of LM4856LQX/NOPB

• Operational Class: Class-AB
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.5@8Ohm@400mW%
• Single Supply Voltage (typ): 3V
• Dual Supply Voltage (typ): Not RequiredV
• Supply Current (max): 12@5VmA
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 68dB
• Single Supply Voltage (min): 2.6V
• Single Supply Voltage (max): 5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 24
• Package Type: LLP
• Lead Free Status / Rohs Status: Compliant

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Application Information
EXPOSED-DAP MOUNTING CONSIDERATIONS
The LM4856’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 area heatsink, copper traces, ground plane, and
finally, surrounding air. The result is a low voltage audio
power amplifier that produces 1.1W dissipation in a 8Ω load
at ≤ 1% THD+N. This high power is achieved through careful
consideration of necessary thermal design. Failing to opti-
mize thermal design may compromise the LM4856’s high
power performance and activate unwanted, though neces-
sary, 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 then, ideally,
V4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
V3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
V2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
(Continued)
TABLE 3. Volume Control
V1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
16
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 two-sided or multi-layer PCB. (The heat sink area
can also be placed on an inner layer of a multi-layer board.
The thermal resistance, however, will be higher.) Connect
the DAP copper pad to the inner layer or backside copper
heat sink area with 6 (3 X 2) (LD) vias. The via diameter
should be 0.012in - 0.013in with a 1.27mm pitch. Ensure
efficient thermal conductivity by plugging and tenting the vias
with plating and solder mask, respectively.
Best thermal performance is achieved with the largest prac-
tical copper heat sink area. If the heatsink and amplifier
share the same PCB layer, a nominal 2.5in
necessary for 5V operation with a 4Ω load. Heatsink areas
V0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
R
OUT
R
-34.5
-33.0
-31.5
-30.0
-28.5
-27.0
-25.5
-24.0
-22.5
-21.0
-19.5
-18.0
-16.5
-15.0
-13.5
-12.0
-10.5
IN
10.5
12.0
-9.0
-7.5
-6.0
-4.5
-3.0
-1.5
0.0
1.5
3.0
4.5
6.0
7.5
9.0
G2
to
, L
, L
IN
OUT
Gain (dB)
R
OUT
-40.5
-39.0
-37.5
-36.0
-34.5
-33.0
-31.5
-30.0
-28.5
-27.0
-25.5
-24.0
-22.5
-21.0
-19.5
-18.0
-16.5
-15.0
-13.5
-12.0
-10.5
2
P
-9.0
-7.5
-6.0
-4.5
-3.0
-1.5
0.0
1.5
3.0
4.5
6.0
G1
to
(min) area is
HS
, L
OUT