LM4941SD/NOPB National Semiconductor, LM4941SD/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM4941SD/NOPB
• Description: IC AMP AUDIO PWR 1.54W MONO 8LLP
• Manufacturer: National Semiconductor
• Series: Boomer®, PowerWise®r
• Type: Class ABr

Specifications of LM4941SD/NOPB

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 1.54W x 1 @ 8 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Features: Depop, Differential Inputs, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 8-LLP
• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 1-Channel Mono
• Output Power (typ): 1.54x1@8OhmW
• Audio Amplifier Function: Speaker
• Total Harmonic Distortion: 0.04@8Ohm@0.7W%
• 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: 95dB
• 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: 8
• Package Type: LLP EP
• Amplifier Class: AB
• No. Of Channels: 1
• Output Power: 1.25W
• Supply Voltage Range: 2.4V To 5.5V
• Load Impedance: 8ohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: LLP
• Rohs Compliant: Yes
• For Use With: LM4941SDBD - BOARD EVALUATION LM4941
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4941SD; LM4941SDTR

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Application Information
OPTIMIZING RF IMMUNITY
The internal circuitry of the LM4941 suppresses the amount
of RF signal that is coupled into the chip. However, certain
external factors, such as output trace length, output trace ori-
entation, distance between the chip and the antenna, antenna
strength, speaker type, and type of RF signal, may affect the
RF immunity of the LM4941. In general, the RF immunity of
the LM4941 is application specific. Nevertheless, optimal RF
immunity can be achieved by using short output traces and
increasing the distance between the LM4941 and the anten-
na.
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4941 is a fully differential audio amplifier that features
differential input and output stages. Internally this is accom-
plished by two circuits: a differential amplifier and a common
mode feedback amplifier that adjusts the output voltages so
that the average value remains V
ferential gain, the amplifier can be considered to have
"halves". Each half uses an input and feedback resistor (R
and R
With R
half. This results in a differential gain of
It is extremely important to match the input resistors to each
other, as well as the feedback resistors to each other for best
amplifier performance. See the Proper Selection of Exter-
nal Components section for more information. A differential
amplifier works in a manner where the difference between the
two input signals is amplified. In most applications, input sig-
nals will be 180° out of phase with each other. The LM4941
can be used, however, as a single-ended input amplifier while
still retaining its fully differential benefits because it simply
amplifies the difference between the inputs.
All of these applications provide what is known as a "bridged
mode" output (bridge-tied-load, BTL). This results in output
signals that are 180° out of phase with respect to 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 configuration: it
provides differential drive to the load, thus doubling 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 attain-
able output power assumes that the amplifier is not current
limited or clipped. In order to choose an amplifier's closed-
loop gain without causing excess clipping, please refer to the
Audio Power Amplifier Design section.
A bridged configuration, such as the one used in the LM4941,
also creates a second advantage over single-ended ampli-
fiers. Since the differential outputs are biased at half-supply,
no net DC voltage exists across the load. This assumes that
the input resistor pair and the feedback resistor pair are prop-
erly matched (see Proper Selection of External Compo-
nents). BTL configuration eliminates the output coupling
capacitor required in single-supply, single-ended amplifier
configurations. If an output coupling capacitor is not used in
F
i1
) to set its respective closed-loop gain (see Figure 1).
= R
i2
and R
F1
A
= R
VD
F2
= -R
, the gain is set at -R
F
/R
DD
i
/ 2. When setting the dif-
F
/ R
i
for each
(1)
i
8
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 LM4941 include in-
creased power supply rejection ratio, common-mode noise
reduction, and click and pop reduction.
POWER DISSIPATION
Power dissipation is a major concern when designing a suc-
cessful amplifier, whether the amplifier is bridged or single-
ended. Equation 2 states the maximum power dissipation
point for a single-ended amplifier operating at a given supply
voltage and driving a specified output load.
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in
internal power dissipation versus a single-ended amplifier op-
erating at the same conditions.
Since the LM4941 has bridged outputs, the maximum internal
power dissipation is four times that of a single-ended ampli-
fier. Even with this substantial increase in power dissipation,
the LM4941 does not require additional heatsinking under
most operating conditions and output loading. From Equation
3, assuming a 5V power supply and an 8Ω load, the maximum
power dissipation point is 625mW. The maximum power dis-
sipation point obtained from Equation 3 must not be greater
than the power dissipation results from Equation 4:
The LM4941's θ
Depending on the ambient temperature, T
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 decreased, the load
impedance increased, the ambient temperature reduced, or
the θ
near the output, V
θ
allowing higher power dissipation. For the typical application
of a 5V power supply, with an 8Ω load, the maximum ambient
temperature possible without violating the maximum junction
temperature is approximately 87.5°C provided that device
operation is around the maximum power dissipation point.
Recall that internal power dissipation is a function of output
power. If typical operation is not around the maximum power
dissipation point, the LM4941 can operate at higher ambient
temperatures. Refer to the Typical Performance Charac-
teristics curves for power dissipation information.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is crit-
ical for low noise performance and high power supply rejec-
tion ratio (PSRR). The capacitor location on both the bypass
and power supply pins should be as close to the device as
possible. Typical applications employ a 5V regulator with
10µF and 0.1µF bypass capacitors that increase supply sta-
JA
. The larger areas of copper provide a form of heatsinking
JA
P
reduced with heatsinking. In many cases, larger traces
P
DMAX
DMAX
= 4 * (V
P
= (V
DMAX
JA
DD
DD
in an TMD09AAA package is 100°C/W.
, and GND pins can be used to lower the
DD
)
= (T
2
)
/ (2π
2
JMAX
/ (2π
2
R
2
- T
L
R
) Single-Ended
L
A
) Bridge Mode
) / θ
JA
A
, of the system
(2)
(3)
(4)