LM4950TSBD National Semiconductor, LM4950TSBD Datasheet - Page 16

• Manufacturer Part Number: LM4950TSBD
• Description: BOARD EVALUATION LM4950TS
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4950TSBD

• Amplifier Type: Class AB
• Output Type: 1-Channel (Mono) or 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 7.5W x 1 @ 8 Ohm; 3.1W x 2 @ 4 Ohm
• Voltage - Supply: 9.6 V ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4950
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Application Information
The LM4950’s dissipation is twice the value given by Equa-
tion (2) when driving two SE loads. For a 12V supply and two
8Ω SE loads, the LM4950’s dissipation is 1.82W.
The LM4950’s dissipation when driving a BTL load is given
by Equation (3). For a 12V supply and a single 8Ω BTL load,
the dissipation is 3.65W.
The maximum power dissipation point given by Equation (3)
must not exceed the power dissipation given by Equation
(4):
The LM4950’s T
LM4950’s θ
copper plane of at least 16in
tween the top and bottom layers of a two-sided PCB. Con-
nect the two layers together under the tab with a 5x5 array of
vias. For the TA package, use an external heatsink with a
thermal impedance that is less than 20˚C/W. At any given
ambient temperature T
mum internal power dissipation supported by the IC packag-
ing. Rearranging Equation (4) and substituting P
P
mum ambient temperature that still allows maximum stereo
power dissipation without violating the LM4950’s maximum
junction temperature.
For a typical application with a 12V power supply and a BTL
8Ω load, the maximum ambient temperature that allows
maximum stereo power dissipation without exceeding the
maximum junction temperature is approximately 77˚C for the
TS package.
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 operating
around the maximum power dissipation point. Since internal
power dissipation is a function of output power, higher am-
bient temperatures are allowed as output power or duty
cycle decreases.
If the result of Equation (3) is greater than that of Equation
(4), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. Further,
ensure that speakers rated at a nominal 4Ω (SE operation)
or 8Ω (BTL operation) do not fall below 3Ω or 6Ω, respec-
tively. If these measures are insufficient, a heat sink can be
added to reduce θ
JMAX
DMAX
P
DMAX-MONOBTL
. If the result violates the LM4950’s 150˚C, reduce the
’ results in Equation (5). This equation gives the maxi-
P
DMAX-SE
JA
T
T
is 20˚C/W when the metal tab is soldered to a
JMAX
A
P
= T
= (V
DMAX
JMAX
JA
= P
JMAX
= 4(V
. The heat sink can be created using
DD
’ = (T
A
= 150˚C. In the TS package, the
DMAX-MONOBTL
)
, use Equation (4) to find the maxi-
- P
2
DD
/ (2π
JMAX
DMAX-MONOBTL
)
2
2
. This plane can be split be-
2
/ 2π
R
- T
L
): Single Ended
2
A
R
) / θ
θ
L
JA
: Bridge Mode (3)
JA
+ T
(Continued)
θ
JA
A
DMAX
(2)
(4)
(5)
(6)
for
16
additional copper area around the package, with connec-
tions to the ground pins, supply pin and amplifier output pins.
Refer to the Typical Performance Characteristics curves
for power dissipation information at lower output power lev-
els.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding
the voltage applied to any pin, with respect to ground, as
listed in the Absolute Maximum Ratings section.
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 voltage regulator typi-
cally use a 10µF in parallel with a 0.1µF 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 1.0µF
tantalum bypass capacitance connected between the
LM4950’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 LM4950’s power supply pin and
ground as short as possible. Connecting a 10µF capacitor,
C
the internal bias voltage’s stability and improves the amplifi-
er’s PSRR. The PSRR improvements increase as the by-
pass pin capacitor value increases. Too large, however,
increases turn-on time and can compromise the amplifier’s
click and pop performance. The selection of bypass capaci-
tor values, especially C
requirements, click and pop performance (as explained in
the section, SELECTING EXTERNAL COMPONENTS),
system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4950 features an active-low micro-power shutdown
mode. When active, the LM4950’s micro-power shutdown
feature turns off the amplifier’s bias circuitry, reducing the
supply current. The low 40µA typical shutdown current is
achieved by applying a voltage to the SHUTDOWN pin that
is as near to GND as possible. A voltage that is greater than
GND may increase the shutdown current.
There are a few methods to control the micro-power shut-
down. These include using a single-pole, single-throw switch
(SPST), a microprocessor, or a microcontroller. When using
a switch, connect a 100kΩ pull-up resistor between the
SHUTDOWN pin and V
parallel with the SPST switch connected between the SHUT-
DOWN pin and GND. The two resistors form a voltage
divider that ensures that the voltage applied to the SHUT-
DOWN pin does not exceed V
operation by opening the switch. Closing the switch applies
GND to the SHUTDOWN pin, activating micro-power shut-
down. The switch and resistor guarantee that the SHUT-
DOWN pin will not float. This prevents unwanted state
changes. In a system with a microprocessor or a microcon-
troller, use a digital output to apply the active-state voltage to
the SHUTDOWN pin. Again, ensure that the microcontroller
or microprocessor logic-high signal does not exceed the
LM4950’s V
BYPASS
, between the BYPASS pin and ground improves
DD
/2 SHUTDOWN signal limit.
BYPASS
DD
and a second 100kΩ resistor in
DD
, depends on desired PSRR
/2. Select normal amplifier