LM4804LQX/NOPB National Semiconductor, LM4804LQX/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM4804LQX/NOPB
• Description: IC AMP AUDIO PWR 1.9W MONO 28LLP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4804LQX/NOPB

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 1.9W x 1 @ 8 Ohm
• Voltage - Supply: 2.7 V ~ 6.1 V
• Features: Depop, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 28-LLP
• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 1-Channel Mono
• Output Power (typ): 1.9x1@8OhmW
• Audio Amplifier Function: Speaker
• Total Harmonic Distortion: 0.13@8Ohm@1.5W%
• Single Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (typ): 3/5V
• Power Supply Requirement: Dual
• Power Dissipation: 1.8W
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 72dB
• Single Supply Voltage (min): Not RequiredV
• Single Supply Voltage (max): Not RequiredV
• Dual Supply Voltage (min): 2.7/3V
• Dual Supply Voltage (max): 5/6.1V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 28
• Package Type: LLP EP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Application Information
BRIDGE CONFIGURATION EXPLANATION
Audio Amplifier portion of the LM4804 has two operational
amplifiers internally, allowing for a few different amplifier
configurations. The first amplifier’s gain is externally config-
urable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of Rf to Ri while
the second amplifier’s gain is fixed by the two internal 20kΩ
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both
amplifiers producing signals identical in magnitude, but out
of phase by 180˚. Consequently, the differential gain for the
IC is
By driving the load differentially through outputs Vo1 and
Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classical single-ended amplifier configura-
tion where one side of the load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential
drive to the load, thus doubling output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same con-
ditions. This increase in attainable output power assumes
that the amplifier is not current limited or clipped. In order to
choose an amplifier’s closed-loop gain without causing ex-
cessive clipping, please refer to the Audio Power Amplifier
Design section.
A bridge configuration also creates a second advantage over
single-ended amplifiers. Since the differential outputs, Vo1
and Vo2, are biased at half-supply, no net DC voltage exists
across the load. This eliminates the need for an output
coupling capacitor which is required in a single supply,
single-ended amplifier configuration. Without an output cou-
pling capacitor, the half-supply bias across the load would
result in both increased internal IC power dissipation and
also possible loudspeaker damage.
AMPLIFIER POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation. Since the amplifier portion of the
LM4804 has two operational amplifiers, the maximum inter-
nal power dissipation is 4 times that of a single-ended am-
plifier. The maximum power dissipation for a given BTL
application can be derived from Equation 1.
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON time of the FET
means the maximum output current will be determined by
power dissipation within the LM2731 FET switch. The switch
power dissipation from ON-state conduction is calculated by
Equation 2.
P
DMAX(SWITCH)
P
DMAX(AMP)
A
= DC x I
VD
= 4(V
= 2 *(Rf/Ri)
IND
DD
(AVE)
)
2
/ (2π
2
2
x R
R
L
)
DS
(ON)
(1)
(2)
8
There will be some switching losses as well, so some derat-
ing needs to be applied when calculating IC power dissipa-
tion.
TOTAL POWER DISSIPATION
The total power dissipation for the LM4804 can be calculated
by adding Equation 1 and Equation 2 together to establish
Equation 3:
The result from Equation 3 must not be greater than the
power dissipation that results from Equation 4:
For package LQA28A, θ
LM4804. Depending on the ambient temperature, T
system surroundings, Equation 4 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 3 is greater than that of
Equation 4, then either the supply voltage must be in-
creased, the load impedance increased or T
the typical application of a 3V power supply, with V1 set to
6.0V and 8Ω load, the maximum ambient temperature pos-
sible without violating the maximum junction temperature is
approximately TBD˚C provided that device operation is
around the maximum power dissipation point. Thus, for typi-
cal applications, power dissipation is not an issue. Power
dissipation is a function of output power and thus, if typical
operation is not around the maximum power dissipation
point, the ambient temperature may be increased accord-
ingly. Refer to the Typical Performance Characteristics
curves for power dissipation information for lower output
levels.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4804’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
LD package should have its DAP soldered to a copper pad
on the PCB. The DAP’s PCB copper pad may be connected
to a large plane of continuous unbroken copper. This plane
forms a thermal mass, heat sink, and radiation area. Further
detailed and specific information concerning PCB layout,
fabrication, and mounting an LD (LLP) package is available
from National Semiconductor’s Package Engineering Group
under application note AN1187.
SHUTDOWN FUNCTION
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry to provide a
quick, smooth transition into shutdown. Another solution is to
use a single-pole, single-throw switch, in conjunction with an
external pull-up resistor to drive both shutdown pins simul-
taneously. When the switch is closed, the shutdown pin is
connected to ground which disables the amplifier. If the
switch is open, then the external pull-up resistor to V
enable the LM4804. This scheme guarantees that the shut-
down pins will not float thus preventing unwanted state
changes.
2π
2
P
R
P
DMAX
L
DMAX(TOTAL)
]+[DCxI
= (T
JA
IND
= 59˚C/W. T
JMAX
(AVE)
= [4*(V
- T
2
A
xR
) / θJA
DD
DS
JMAX
)
2
(ON)]
/
= 125˚C for the
A
reduced. For
A
, of the
DD
will
(3)
(4)