LM4875MX/NOPB National Semiconductor, LM4875MX/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM4875MX/NOPB
• Description: IC AMP AUDIO PWR 1W MONO 8SOIC
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4875MX/NOPB

• Output Type: 1-Channel (Mono) with Mono Headphones
• Max Output Power X Channels @ Load: 1W x 1 @ 8 Ohm; 110mW x 1 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Depop, Mute, Shutdown, Thermal Protection, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Operational Class: Class-AB
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.6@8Ohm@300mW%
• 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: 50dB
• Single Supply Voltage (min): 2.7V
• 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: SOIC N
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4875MX

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Application Information
of a single-ended amplifier. However, even with this substan-
tial increase in power dissipation, the LM4875 does not
require heatsinking. From Equation (2), assuming a 5V
power supply and an 8Ω load, the maximum power dissipa-
tion point is 633 mW. The maximum power dissipation point
obtained from Equation (2) must not be greater than the
power dissipation that results from Equation (3):
For the SO package, θ
has a 190˚C/W θ
given ambient temperature T
find the maximum internal power dissipation supported by
the IC packaging. If the result of Equation (2) is greater than
that of Equation (3), then either decrease the supply voltage,
increase the load impedance, or reduce the ambient tem-
perature. For a typical application using the SO packaged
LM4875, a 5V power supply, and an 8Ω load, the maximum
ambient temperature that does not violate the maximum
junction temperature is approximately 55˚C. The maximum
ambient temperature for the MSOP package with the same
conditions is approximately 30˚C. These results further as-
sume that a device is a surface mount part operating around
the maximum power dissipation point. Since internal power
dissipation is a function of output power, higher ambient
temperatures are allowed as output power decreases. Refer
to the Typical Performance Characteristics curves for
power dissipation information at lower output power levels.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitors connected to the bypass and power
supply pins should be placed as close to the LM4875 as
possible. The capacitor connected between the bypass pin
and ground improves the internal bias voltage’s stability,
producing improved PSRR. The improvements to PSRR
increase as the bypass pin capacitor value increases. Typi-
cal applications employ a 5V regulator with 10µF and a
0.1µF filter capacitors that aid in supply stability. Their pres-
ence, however does not eliminate the need for bypassing the
supply nodes of the LM4875. The selection of bypass ca-
pacitor values, especially C
requirements, click and pop performance (as explained in
the section, Proper Selection of External Components),
system cost, and size constraints.
DC VOLTAGE VOLUME CONTROL
The LM4875’s internal volume control is controlled by the DC
voltage applied its DC Vol/SD pin (pin 4). The volume con-
trol’s input range is from GND to V
typical volume response versus input control voltage is
shown in the Typical Performance Characteristicssection.
The DC Vol/SD pin also functions as the control pin for the
LM4875’s micropower shutdown feature. See the Mute and
Shutdown Function section for more information.
Like all volume controls, the Lm4875’s internal volume con-
trol is set while listening to an amplified signal that is applied
to an external speaker. The actual voltage applied to the DC
Vol/SD pin is a result of the volume a listener desires. As
such, the volume control is designed for use in a feedback
system that includes human ears and preferences. This
feedback system operates quite well without the need for
accurate gain. The user simply sets the volume to the de-
sired level as determined by their ear, without regard to the
P
JA
DMAX
. T
JMAX
JA
= (T
= 150˚C/W. The MSOP package
= 150˚C for the LM4875. For a
B
JMAX
A
, depends on desired PSRR
, Equation (3) can be used to
–T
DD
A
)/θ
. A graph showing a
JA
(Continued)
(3)
8
actual DC voltage that produces the volume. Therefore, the
accuracy of the volume control is not critical, as long as
volume changes monotonically and step size is small
enough to reach a desired volume that is not too loud or too
soft. Since gain accuracy is not critical, there may be a
volume variation from part-to-part even with the same ap-
plied DC control voltage. The gain of a given LM4875 can be
set with a fixed external voltage, but another LM4875 may
require a different control voltage to achieve the same gain.
Figure 2 is a curve showing the volume variation of seven
typical LM4875s as the voltage applied to the DC Vol/SD pin
is varied. For gains between -20dB and +16dB, the typical
part-to-part variation is typically
voltage.
MUTE AND SHUTDOWN FUNCTION
The LM4875’s mute and shutdown functions are controlled
through the DC Vol/SD pin. Mute is activated by applying a
voltage in the range of 500mV to 1V. A typical attenuation of
75dB is achieved is while mute is active. The LM4875’s
micropower shutdown mode turns off the amplifier’s bias
circuitry. The micropower shutdown mode is activated by
applying less than 300mV
shutdown is active, they supply current is reduced to 0.7µA
(typ). A degree of uncertainty exists when the voltage applied
to the DC Vol/SD pin is in the range of 300mV to 500mV. The
LM4875 can be in mute, still fully powered, or in micropower
shutdown and fully muted. In mute mode, the LM4875 draws
the typical quiescent supply current. The DC Vol/SD pin
should be tied to GND for best shutdown mode performance.
As the DC Vol/SD is increased above 0.5V the amplifier will
follow the attenuation curve in Typical Performance Char-
acteristics.
HP-Sense FUNCTION
Applying a voltage between 4V and V
HP-Sense headphone control pin turns off Amp2 and mutes
a bridged-connected load. Quiescent current consumption is
reduced when the IC is in this single-ended mode.
Figure 3 shows the implementation of the LM4875’s head-
phone control function. With no headphones connected to
the headphone jack, the R1-R2 voltage divider sets the
voltage applied to the HP-Sense pin (pin 3) at approximately
50mV. This 50mV enables the LM4875 and places it in
bridged mode operation.
FIGURE 2. Typical part-to-part gain variation as a
function of DC-Vol control voltage
DC
to the DC Vol/SD pin. When
±
1dB for a given control
CC
to the LM4875’s
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