LM4899ITL/NOPB National Semiconductor, LM4899ITL/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM4899ITL/NOPB
• Description: IC AMP AUDIO PWR 1.4W MONO 9USMD
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4899ITL/NOPB

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 1.4W x 1 @ 4 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Features: Depop, Differential Inputs, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 9-MicroSMD
• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 1-Channel Mono
• Output Power (typ): 1x1@8OhmW
• Audio Amplifier Function: Speaker
• Total Harmonic Distortion: 0.05@8Ohm@400mW%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 90dB
• Single Supply Voltage (min): 2.4V
• Single Supply Voltage (max): 5.5V
• 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: 9
• Package Type: uSMD
• For Use With: LM4899ITLBD - BOARD EVALUATION LM4899ITL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM4899ITL; *LM4899ITL/NOPB; LM4899ITL

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Application Information
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4899 is a fully differential audio amplifier that fea-
tures differential input and output stages. Internally this is
accomplished by two circuits: a differential amplifier and a
common mode feedback amplifier that adjusts the output
voltages so that the average value remains V
LM4899 features precisely matched internal gain-setting re-
sistors, thus eliminating the need for external resistors and
fixing the differential gain at A
A differential amplifier works in a manner where the differ-
ence between the two input signals is amplified. In most
applications, this would require input signals that are 180˚
out of phase with each other.
The LM4899 provides what is known as a "bridged mode"
output (bridge-tied-load, BTL). This results in output signals
at V
each other. Bridged mode operation is different from the
single-ended amplifier configuration that connects the load
between the amplifier output and ground. A bridged amplifier
design has distinct advantages over the single-ended con-
figuration: it provides differential drive to the load, thus dou-
bling maximum possible output swing for a specific supply
voltage. Four times the output power is possible compared
with a single-ended amplifier under the same conditions.
This increase in attainable output power assumes that the
amplifier is not current limited or clipped.
A bridged configuration, such as the one used in the
LM4899, also creates a second advantage over single-
ended amplifiers. Since the differential outputs, V
are biased at half-supply, no net DC voltage exists across
the load. BTL configuration eliminates the output coupling
capacitor required in single-supply, single-ended amplifier
configurations. If an output coupling capacitor is not used in
a single-ended output configuration, the half-supply bias
across the load would result in both increased internal IC
power dissipation as well as permanent loudspeaker dam-
age. Further advantages of bridged mode operation specific
to fully differential amplifiers like the LM4899 include in-
creased power supply rejection ratio, common-mode noise
reduction, and click and pop reduction.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4899’s exposed-DAP (die attach paddle) package
(LD) provide 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, finally, surrounding
air. The result is a low voltage audio power amplifier that
produces 1.4W at ≤ 1% THD with a 4Ω load. This high power
is achieved through careful consideration of necessary ther-
mal design. Failing to optimize thermal design may compro-
mise the LM4899’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 and heat sink and radiation area.
Place the heat sink area on either outside plane in the case
of a two-sided PCB, or on an inner layer of a board with more
o1
and V
o2
that are 180˚ out of phase with respect to
VD
= 6dB.
o1
DD
and V
/2. The
o2
,
12
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 0.050in
pitch. Ensure efficient thermal conductivity by plating-
through and solder-filling the vias.
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
not placed on the same PCB layer as the LM4899 should be
5in
The last two area recommendations apply for 25˚C ambient
temperature. In all circumstances and conditions, the junc-
tion temperature must be held below 150˚C to prevent acti-
vating the LM4899’s thermal shutdown protection. The
LM4899’s power de-rating curve in the Typical Performance
Characteristics shows the maximum power dissipation ver-
sus temperature. Example PCB layouts for the exposed-
DAP TSSOP and LLP packages are shown in the Demon-
stration Board Layout section. Further detailed and specific
information concerning PCB layout, fabrication, and mount-
ing an LLP package is available from National Semiconduc-
tor’s package Engineering Group under application note AN-
1187.
PCB LAYOUT AND SUPPLY REGULATION
CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω LOADS
Power dissipated by a load is a function of the voltage swing
across the load and the load’s impedance. As load imped-
ance decreases, load dissipation becomes increasingly de-
pendent on the interconnect (PCB trace and wire) resistance
between the amplifier output pins and the load’s connec-
tions. Residual trace resistance causes a voltage drop,
which results in power dissipated in the trace and not in the
load as desired. For example, 0.1Ω trace resistance reduces
the output power dissipated by a 4Ω load from 1.4W to
1.37W. This problem of decreased load dissipation is exac-
erbated as load impedance decreases. Therefore, to main-
tain the highest load dissipation and widest output voltage
swing, PCB traces that connect the output pins to a load
must be as wide as possible.
Poor power supply regulation adversely affects maximum
output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply
voltage causes decreased headroom, output signal clipping,
and reduced output power. Even with tightly regulated sup-
plies, trace resistance creates the same effects as poor
supply regulation. Therefore, making the power supply
traces as wide as possible helps maintain full output voltage
swing.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifer, whether the amplifier is bridged or
single-ended. Equation 2 states the maximum power dissi-
pation point for a single-ended amplifier operating at a given
supply voltage and driving a specified output load.
2
(min) for the same supply voltage and load resistance.
P
DMAX
= (V
DD
)
2
/ (2π
2
R
L
) Single-Ended
2
(min) area is
(1)