LM4866MTE National Semiconductor, LM4866MTE Datasheet - Page 12

• Manufacturer Part Number: LM4866MTE
• Description: 2.2W Stereo Audio Amplifier
• Manufacturer: National Semiconductor

www.national.com
Application Information
fier. From Equation (3), assuming a 5V power supply and an
4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
The LM4973’s power dissipation is twice that given by Equa-
tion (2) or Equation (3) when operating in the single-ended
mode or bridge mode, respectively. Twice the maximum
power dissipation point given by Equation (3) must not ex-
ceed the power dissipation given by Equation (4):
The LM4866’s T
soldered to a DAP pad that expands to a copper area of 5in
on a PCB, the LM4866’s θ
soldered to a DAP pad that expands to a copper area of 2in
on a PCB , the LM4866’s θ
ambient temperature T
mum internal power dissipation supported by the IC packag-
ing. Rearranging Equation (4) and substituting PDMAX for
PDMAX’ results in Equation (5). This equation gives the
maximum ambient temperature that still allows maximum
stereo power dissipation without violating the LM4866’s
maximum junction temperature.
For a typical application with a 5V power supply and an 4Ω
load, the maximum ambient temperature that allows maxi-
mum stereo power dissipation without exceeding the maxi-
mum junction temperature is approximately 99˚C for the LLP
package and 45˚C for the MTE package.
Equation (6) gives the maximum junction temperature T
MAX
maximum junction temperature by reducing the power sup-
ply voltage or increasing the load resistance. Further allow-
ance should be made for increased ambient temperatures.
The above examples 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 or duty cycle decreases.
If the result of Equation (2) is greater than that of Equation
(3), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to
reduce θ
copper area around the package, with connections to the
ground pin(s), supply pin and amplifier output pins. External,
solder attached SMT heatsinks such as the Thermalloy
7106D can also improve power dissipation. When adding a
heat sink, the θ
junction−to−case thermal impedance,
. If the result violates the LM4866’s 150˚C, reduce the
P
JA
DMAX
. The heat sink can be created using additional
JA
= 4 x (V
T
P
A
JMAX
DMAX
T
is the sum of θ
JMAX
= T
’ = (T
JMAX
J\A
= 150˚C. In the LQ (LLP) package
DD
= P
, use Equation (4) to find the maxi-
JA
)
2
− 2 x P
JMAX
DMAX
/ (2π
is 20˚C/W. In the MTE package
JA
JC
2
− T
θ
is 41˚C/W. At any given
, θ
R
JA
DMAX
L
A
CS
) Bridge Mode
+ T
CS
) / θ
, and θ
is the case−to−sink
θ
A
JA
(Continued)
JA
SA
. (θ
JC
is the
(3)
(4)
(5)
(6)
J -
2
2
12
thermal impedance, and θ
impedance.) Refer to the Typical Performance Characteris-
tics 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. Applications that employ a 5V regulator typically
use a 10µF in parallel with a 0.1µF filter capacitors to stabi-
lize the regulator’s output, reduce noise on the supply line,
and improve the supply’s transient response. However, their
presence does not eliminate the need for a local 1.0µF
tantalum bypass capacitance connected between the
LM4866’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation in the output signal. Keep the length of leads and
traces that connect capacitors between the LM4866’s power
supply pin and ground as short as possible. Connecting a
1µF capacitor, C
improves the internal bias voltage’s stability and improves
the amplifier’s PSRR. The PSRR improvements increase as
the bypass pin capacitor value increases. Too large, how-
ever, increases turn-on time and can compromise amplifier’s
click and pop performance. The selection of bypass capaci-
tor values, especially C
ments, click and pop performance (as explained in the sec-
tion, Proper Selection of External Components), system
cost, and size constraints.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4866’s shutdown function. Activate micro-power shut-
down by applying V
the LM4866’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically V
shutdown current is achieved by applying a voltage that is as
near as V
thrat is less than V
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 10kΩ pull-up resistor between the
SHUTDOWN pin and V
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V
ing micro-power shutdown. The switch and resistor guaran-
tee that the SHUTDOWN pin will not float. This prevents
unwanted state changes. In a system with a microprocessor
or a microcontroller, use a digital output to apply the control
voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin
with active circuitry eliminates the pull up resistor.
TABLE 1. LOGIC LEVEL TRUTH TABLE FOR SHUT-
DOWN OPERATION
SHUTDOWN
DD
as possible to the SHUTDOWN pin. A voltage
High
Low
B
, between the BYPASS pin and ground
DD
DD
DD
may increase the shutdown current.
to the SHUTDOWN pin. When active,
B
DD
, depends on desired PSRR require-
through the pull-up resistor, activat-
. Connect the switch between the
SA
OPERATIONAL MODE
Micro-power Shutdown
Full power, stereo BTL
is the sink−to−ambient thermal
DD
/2. The low 0.7µA typical
amplifiers