LM4865M National Semiconductor, LM4865M Datasheet - Page 9

• Manufacturer Part Number: LM4865M
• Description: IC, AUDIO PWR AMP, CLASS AB 750mW, SOIC8
• Manufacturer: National Semiconductor

Specifications of LM4865M

• Audio Control Type: Volume
• Output Power: 1W
• Control / Process Application: GSM Phones And Accessories, DECT, Office Phones, Hand Held Radio
• Supply Voltage Range: 2.7V To 5.5V
• No. Of Channels: 1
• Thd + N: 0.6% @ 8ohm, VDD=5V
• Load Impedance: 8ohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: MSOP
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
of a single-ended amplifier. However, even with this substan-
tial increase in power dissipation, the LM4865 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 micro SMD and SO packages, θ
MSO package has a 190˚C/W θ
LM4865. For a given ambient temperature T
can be used to 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 temperature. For a typical application using the
micro SMD or SO packaged LM4865, a 5V power supply,
and an 8Ω load, the maximum ambient temperature that
does not violate the maximum junction temperature is ap-
proximately 55˚C. The maximum ambient temperature for
the MSO package with the same conditions is approximately
30˚C. These results further assume 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 Char-
acteristics 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 LM4865 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 LM4865. 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 LM4865 has internal volume control that is controlled by
the DC voltage applied its DC Vol/SD pin (pin 5 on the micro
SMD and pin 4 on the MSOP and SOP packages). The
volume control’s input range is from GND to V
showing a typical volume response versus input control
voltage is shown in the Typical Performance Characteris-
ticssection. The DC Vol/SD pin also functions as the control
pin for the LM4865’s micropower shutdown feature. See
theShutdown Function section for more information.
Like all volume controls, the LM4865’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
P
DMAX
= (T
B
JMAX
, depends on desired PSRR
JA
–T
. T
A
)/θ
JMAX
JA
JA
(Continued)
= 150˚C/W. The
= 150˚C for the
A
, Equation (3)
DD
. A graph
(3)
9
accurate gain. The user simply sets the volume to the de-
sired level as determined by their ear, without regard to the
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 will be volume
variation from part-to-part even with the same applied DC
control voltage. The gain of a given LM4865 can be set with
a fixed external voltage, but another LM4865 may require a
different control voltage to achieve the same gain. Figure 2 is
a curve showing the volume variation of twenty typical
LM4865s as the voltage applied to the DC Vol/SD pin is
varied. For gains greater than unity, the typical part-to-part
variation can be as large as 8dB for the same control volt-
age.
MUTE AND SHUTDOWN FUNCTION
The LM4865’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 LM4865’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
LM4865 can be in mute, still fully powered, or in micropower
shutdown and fully muted. In mute mode, the LM4865 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 LM4865’s head-
phone control function. With no headphones connected to
the headphone jack, the R1-R2 voltage divider sets the
FIGURE 2. Typical part-to-part gain variation as a
function of DC-Vol control voltage
DC
to the DC Vol/SD pin. When
CC
to the LM4865’s
10102547
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