LM4839LQ/NOPB National Semiconductor, LM4839LQ/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM4839LQ/NOPB
• Description: IC AMP AUDIO PWR 2.2W STER 28LLP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4839LQ/NOPB

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 2.2W x 2 @ 3 Ohm; 95mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Bass Boost, Depop, Input Multiplexer, Mute, Shutdown, Thermal Protection, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 28-LLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4839LQ; LM4839LQTR

Application Information
The LM4839 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
4
1.27W or 2.54W for stereo operation.
The LM4839’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 LM4839’s T
to a DAP pad that expands to a copper area of 5in
PCB, the LM4839’s
soldered to a DAP pad that expands to a copper area of 2in
on a PCB, the LM4839’s
package,
T
dissipation supported by the IC packaging. Rearranging
Equation (4) and substituting P
Equation (5). This equation gives the maximum ambient
temperature that still allows maximum stereo power dissipa-
tion without violating the LM4839’s maximum junction tem-
perature.
For a typical application with a 5V power supply and an 4
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 package.
Equation (6) gives the maximum junction temperature
T
duce the maximum junction temperature by reducing the
power supply voltage or increasing the load resistance. Fur-
ther allowance should be made for increased ambient tem-
peratures.
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
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
A
JMAX
, use Equation (4) to find the maximum internal power
load, the maximum single channel power dissipation is
. If the result violates the LM4839’s T
P
JA
DMAX
. The heat sink can be created using additional
JA
= 80˚C/W. At any given ambient temperature
= 4
P
JMAX
T
T
A
DMAX
JMAX
= T
*
(V
= 150˚C. In the LQ package soldered
JA
' = (T
JMAX
DD
= P
is 20˚C/W. In the MTE package
)
JA
2
DMAX
/(2
– 2*P
JMAX
is 41˚C/W. For the LM4839MT
2
DMAX
R
− T
DMAX
L
JA
) Bridge Mode
A
+ T
)/
for P
(Continued)
A
JA
JA
DMAX
JMAX
' results in
150˚C, re-
2
on a
(3)
(4)
(5)
(6)
2
15
heat sink, the
junction-to-case thermal impedance,
thermal impedance, and
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 capacitor 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
LM4839’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 LM4839’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 a capacitor, however,
increases turn-on time and can compromise the 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.
PROPER SELECTION OF EXTERNAL COMPONENTS
Optimizing the LM4839’s performance requires properly se-
lecting external components. Though the LM4839 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4839 is unity-gain stable, giving a designer maximum
design flexibility. The gain should be set to no more than a
given application requires. This allows the amplifier to
achieve minimum THD+N and maximum signal-to-noise ra-
tio. These parameters are compromised as the closed-loop
gain increases. However, low gain circuits demand input
signals with greater voltage swings to achieve maximum
output power. Fortunately, many signal sources such as
audio CODECs have outputs of 1V
refer to the Audio Power Amplifier Design section for more
information on selecting the proper gain.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (0.33µF in Figure 1 ). A high
value capacitor can be expensive and may compromise
space efficiency in portable designs. In many cases, how-
ever, the speakers used in portable systems, whether inter-
nal or external, have little ability to reproduce signals below
150Hz. Applications using speakers with this limited fre-
quency response reap little improvement by using a large
input capacitor.
Besides effecting system cost and size, the input coupling
capacitor has an affect on the LM4835’s click and pop per-
formance. When the supply voltage is first applied, a tran-
sient (pop) is created as the charge on the input capacitor
changes from zero to a quiescent state. The magnitude of
the pop is directly proportional to the input capacitor’s size.
B
, between the BYPASS pin and ground improves the
JA
is the sum of
B
, depends on desired PSRR require-
SA
is the sink-to-ambient thermal
JC
,
RMS
CS
CS
, and
(2.83V
is the case-to-sink
SA
P-P
www.national.com
. (
). Please
JC
is the