LM4873MTE/NOPB National Semiconductor, LM4873MTE/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM4873MTE/NOPB
• Description: IC AMP AUDIO PWR 3W STER 20TSSOP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4873MTE/NOPB

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 3W x 2 @ 3 Ohm; 440mW x 2 @ 8 Ohm
• Voltage - Supply: 2 V ~ 5.5 V
• Features: Depop, Input Multiplexer, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM4873MTE; *LM4873MTE/NOPB; LM4873MTE

Application Information
mode has a distinct advantage over the single-ended con-
figuration: its differential output doubles the voltage swing
across the load. This produces four times the output power
when compared to a single-ended amplifier under the same
conditions. This increase in attainable output power as-
sumes that the amplifier is not current limited or that the
output signal is not clipped. To ensure minimum output sig-
nal clipping when choosing an amplifier’s closed-loop gain,
refer to the Audio Power Amplifier Design section.
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply, single-
ended amplifiers require. Eliminating an output coupling ca-
pacitor in a single-ended configuration forces a single-supply
amplifier’s half-supply bias voltage across the load. This
increases internal IC power dissipation and may perma-
nently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. 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 higher internal
power dissipation for the same conditions.
The LM4873 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended ampli-
fier. From Equation (3), assuming a 5V power supply and a
4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
The LM4873’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 LM4873’s T
to a DAP pad that expands to a copper area of 5in
PCB, the LM4873’s θ
packages soldered to a DAP pad that expands to a copper
area of 2in
given ambient temperature T
maximum internal power dissipation supported by the IC
packaging. Rearranging Equation (4) and substituting P
for P
maximum ambient temperature that still allows maximum
stereo power dissipation without violating the LM4873’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 LQ
package and 45˚C for the MTE and MTE-1 packages.
DMAX
P
DMAX
P
' results in Equation (5). This equation gives the
2
DMAX
on a PCB, the LM4873’s θ
= 4
P
JMAX
T
= (V
T
A
DMAX
JMAX
= T
*
DD
(V
JA
= 150˚C. In the LQ package soldered
' = (T
JMAX
DD
)
= P
is 20˚C/W. In the MTE and MTE-1
2
/(2π
)
2
DMAX
/(2π
– 2*P
JMAX
A
2
, use Equation (4) to find the
R
2
L
R
) Single-Ended
θ
− T
DMAX
L
JA
) Bridge Mode
A
+ T
)/θ
JA
θ
A
JA
JA
is 41˚C/W. At any
(Continued)
2
DMAX
on a
(2)
(3)
(4)
(5)
(6)
15
Equation (6) gives the maximum junction temperature
T
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, θ
thermal impedance, and θ
impedance.) Refer to the Typical Performance Character-
istics curves for power dissipation information at lower out-
put 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 10 µF in parallel with a 0.1 µF filter capacitors to
stabilize 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 1.0 µF
tantalum bypass capacitance connected between the
LM4873’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation. Keep the length of leads and traces that connect
capacitors between the LM4873’s power supply pin and
ground as short as possible. Connecting a 1µF capacitor,
C
internal bias voltage’s stability and improves the amplifier’s
PSRR. The PSRR improvements increase as the bypass pin
capacitor value increases. Too large, however, increases
turn-on time and can compromise amplifier’s click and pop
performance. The selection of bypass capacitor values, es-
pecially C
and pop performance (as explained in the section, Selecting
Proper External Components), system cost, and size con-
straints.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4873’s shutdown function. Activate micro-power shut-
down by applying V
the LM4873’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
that is less than V
Table 1 shows the logic signal levels that activate and deac-
tivate micro-power shutdown and headphone amplifier op-
eration.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
JMAX
B
, between the BYPASS pin and ground improves the
. If the result violates the LM4873’s 150˚C, reduce the
JA
B
DD
. The heat sink can be created using additional
, depends on desired PSRR requirements, click
as possible to the SHUTDOWN pin. A voltage
JA
is the sum of θ
DD
DD
to the SHUTDOWN pin. When active,
may increase the shutdown current.
SA
is the sink-to-ambient thermal
DD
/2. The low 0.7 µA typical
JC
, θ
CS
CS
, and θ
is the case-to-sink
SA
www.national.com
. (θ
JC
is the