LM4811LD National Semiconductor, LM4811LD Datasheet - Page 13

• Manufacturer Part Number: LM4811LD
• Description: IC,Audio Amplifier,DUAL,LLCC,10PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM4811LD

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
DIGITAL VOLUME CONTROL
The LM4811’s gain is controlled by the signals applied to the
CLOCK and UP/DN inputs. An external clock is required to
drive the CLOCK pin. At each rising edge of the clock signal,
the gain will either increase or decrease by a 3dB step
depending on the logic voltage level applied to the UP/DN
pin. A logic high voltage level applied to the UP/DN pin
causes the gain to increase by 3dB at each rising edge of the
clock signal. Conversely, a logic low voltage level applied to
the UP/DN pin causes the gain to decrease 3dB at each
rising edge of the clock signal. For both the CLOCK and
UP/DN inputs, the trigger point is 1.4V minimum for a logic
high level, and 0.4V maximum for a logic low level.
There are 16 discrete gain settings ranging from +12dB
maximum to −33dB minimum. Upon device power on, the
amplifier’s gain is set to a default value of 0dB. However,
when coming out of shutdown mode, the LM4811 will revert
back to its previous gain setting.
The LM4811’s CLOCK and UP/DN pins should be de-
bounced in order to avoid unwanted state changes during
transitions between V
operation of the digital volume control. A microcontroller or
microprocessor output is recommended to drive the CLOCK
and UP/DN pins.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. Equation 1 states the maximum power
dissipation point for a single-ended amplifier operating at a
given supply voltage and driving a specified output load.
Since the LM4811 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation 1. Even
with the large internal power dissipation, the LM4811 does
not require heat sinking over a large range of ambient tem-
perature. From Equation 1, assuming a 5V power supply and
a 32Ω load, the maximum power dissipation point is 40mW
per amplifier. Thus the maximum package dissipation point
is 80mW. The maximum power dissipation point obtained
must not be greater than the power dissipation predicted by
Equation 2:
FIGURE 2. Timing Diagram
P
P
DMAX
DMAX
IL
= (T
= (V
and V
JMAX
DD
)
IH
2
− T
. This will ensure correct
/ (2π
A
) / θ
2
R
L
JA
)
20006157
(1)
(2)
13
For the MSOP package, θ
package, θ
a given ambient temperature, T
ings, Equation 2 can be used to find the maximum internal
power dissipation supported by the IC packaging. If the
result of Equation 1 is greater than that of Equation 2, then
either the supply voltage must be decreased, the load im-
pedance increased, or T
in a typical application of a 5V power supply and a 32Ω load,
the maximum ambient temperature possible without violating
the maximum junction temperature is approximately
134.5˚C. This assumes the device operates at maximum
power dissipation and uses surface mount packaging. Inter-
nal power dissipation is a function of output power. If typical
operation is not around the maximum power dissipation
point, operation at higher ambient temperatures is possible.
Refer to the Typical Performance Characteristics curves
for power dissipation information for lower output power
levels.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATION
The LM4811’s exposed-dap (die attach paddle) package
(LD/YD) 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/YD 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.
However, since the LM4811 is designed for headphone ap-
plications, connecting a copper plane to the DAP’s PCB
copper pad is not required. The LM4811’s Power Dissipation
vs Output Power Curve in the Typical Performance Char-
acteristics shows that the maximum power dissipated is just
45mW per amplifier with a 5V power supply and a 32Ω load.
Further detailed and specific information concerning PCB
layout, fabrication, and mounting an LD/YD (LLP) package is
available from National Semiconductor’s Package Engineer-
ing Group under application note AN1187.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and
power supply pins should be as close to the device as
possible. The value of the bypass capacitor directly affects
the LM4811’s half-supply voltage stability and PSRR. The
stability and supply rejection increase as the bypass capaci-
tor’s value increases. Typical applications employ a 5V regu-
lator with 10µF and a 0.1µF bypass capacitors which aid in
supply stability, but do not eliminate the need for bypassing
the supply nodes of the LM4811. The selection of bypass
capacitors, especially C
low frequency PSRR, click and pop performance, (explained
in the section, Proper Selection of External Components),
system cost, and size constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not is use, the
LM4811 features amplifier bias circuitry shutdown. This shut-
down function is activated by applying a logic high to the
SHUTDOWN pin. The trigger point is 1.4V minimum for a
JA
= 63˚C/W. T
B
A
, is thus dependent upon desired
JMAX
JA
reduced. For the MSOP package
= 194˚C/W, and for the LD/YD
= 150˚C for the LM4811. For
A
, of the system surround-
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