LM4911LDX National Semiconductor, LM4911LDX Datasheet - Page 18

• Manufacturer Part Number: LM4911LDX
• Description: IC AMP AUDIO PWR .145W AB 10LLP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4911LDX

• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 145mW x 2 @ 16 Ohm
• Voltage - Supply: 2 V ~ 5.5 V
• Features: Mute, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 10-LLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a suc-
cessful design. When operating in capacitor-coupled mode,
Equation 1 states the maximum power dissipation point for a
single-ended amplifier operating at a given supply voltage
and driving a specified output load.
Since the LM4911 has two operational amplifiers in one pack-
age, the maximum internal power dissipation point is twice
that of the number which results from Equation 1. From Equa-
tion 1, assuming a 3V power supply and an 32Ω load, the
maximum power dissipation point is 14mW per amplifier.
Thus the maximum package dissipation point is 28mW.
When operating in OCL mode, the maximum power dissipa-
tion increases due to the use of the third amplifier as a buffer
and is given in Equation 2:
The maximum power dissipation point obtained from either
Equation 1 or 2 must not be greater than the power dissipation
that results from Equation 3:
For package MUB10A, θ
θ
the ambient temperature, T
Equation 3 can be used to find the maximum internal power
dissipation supported by the IC packaging. If the result of
Equation 1 or 2 is greater than that of Equation 3, then either
the supply voltage must be decreased, the load impedance
increased or T
power supply, with a 32Ω load, the maximum ambient tem-
perature possible without violating the maximum junction
temperature is approximately 144°C provided that device op-
eration is around the maximum power dissipation point. Thus,
for typical applications, power dissipation is not an issue.
Power dissipation is a function of output power and thus, if
typical operation is not around the maximum power dissipa-
tion point, the ambient temperature may be increased ac-
cordingly. Refer to the Typical Performance Characteristics
curves for power dissipation information for lower output pow-
ers.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4911's exposed-DAP (die attach paddle) package
(LD) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. This al-
lows rapid heat transfer from the die to the surrounding PCB
copper traces, ground plane, and surrounding air.
The LD package should have its DAP soldered to a copper
pad on the PCB. The DAP's PCB copper pad may be con-
nected to a large plane of continuous unbroken copper. This
plane forms a thermal mass, heat sink, and radiation area.
Further detailed and specific information concerning PCB lay-
out, fabrication, and mounting an LD (LLP) package is avail-
JA
= 63°C/W. T
P
P
P
A
DMAX
DMAX
DMAX
JMAX
reduced. For the typical application of a 3V
= 150°C for the LM4911. Depending on
= (V
= 4(V
= (T
JA
JMAX
DD
DD
= 190°C/W; for package LDA10A,
)
A
2
)
, of the system surroundings,
2
- T
/ (2
/ (
A
π
π
) / θ
2
2
R
R
JA
L
L
)
)
(1)
(2)
(3)
18
able from National Semiconductor's Package Engineering
Group under application note AN1187.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is important
for low noise performance and high power supply rejection.
The capacitor location on the power supply pins should be as
close to the device as possible.
Typical applications employ a 3V regulator with 10mF tanta-
lum or electrolytic capacitor and a ceramic bypass capacitor
which aid in supply stability. This does not eliminate the need
for bypassing the supply nodes of the LM4911. A bypass ca-
pacitor value in the range of 0.1µF to 1µF is recommended
for C
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4911's shutdown function. Activate micro-power shutdown
by applying a logic-low voltage to the SHUTDOWN pin. When
active, the LM4911's micro-power shutdown feature turns off
the amplifier's bias circuitry, reducing the supply current. The
trigger point varies depending on supply voltage and is shown
in the Shutdown Hysteresis Voltage graphs in the Typical
Performance Characteristics section. The low 0.1µA(typ)
shutdown current is achieved by applying a voltage that is as
near as ground as possible to the SHUTDOWN pin. A voltage
that is higher than ground may increase the shutdown current.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a mi-
croprocessor, or a microcontroller. When using a switch,
connect an external 100kΩ pull-up resistor between the
SHUTDOWN pin and V
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by opening the switch. Closing the switch connects the
SHUTDOWN pin to ground, activating micro-power shut-
down.
The switch and resistor guarantee that the SHUTDOWN pin
will not float. This prevents unwanted state changes. In a sys-
tem with a microprocessor or 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.
Shutdown enable/disable times are controlled by a combina-
tion of C
on/off times from Shutdown. Smaller V
turn on/off time for a given value of C
times also improve the LM4911's resistance to click and pop
upon entering or returning from shutdown. For a 2.4V supply
and C
ter or return from shutdown. This longer shutdown time en-
ables the LM4911 to have virtually zero pop and click
transients upon entering or release from shutdown.
Smaller values of C
of increased pop and click and reduced PSRR. Since shut-
down enable/disable times increase dramatically as supply
voltage gets below 2.2V, this reduced turn-on time may be
desirable if extreme low supply voltage levels are used as this
would offset increases in turn-on time caused by the lower
supply voltage. This technique is not recommended for OCL
mode since shutdown enable/disable times are very fast
(0.5s) independent of supply voltage.
When in cap-coupled mode, some restrictions on the usage
of Mute are in effect when entering or returning from shut-
down. These restrictions require Mute not be toggled imme-
diately following a return or entrance to shutdown for a brief
period. These periods are shown as X1 and X2 and are dis-
S
.
B
= 4.7µF, the LM4911 requires about 2 seconds to en-
B
and V
DD
. Larger values of C
B
will decrease turn-on time, but at the cost
DD
. Connect the switch between the
DD
B
results in longer turn
B
values also increase
. Longer shutdown