LM4916MMX National Semiconductor, LM4916MMX Datasheet - Page 14

• Manufacturer Part Number: LM4916MMX
• Manufacturer: National Semiconductor

Specifications of LM4916MMX

• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 1-Channel Mono/2-Channel Stereo
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.1@8Ohm@25mW%
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 66dB
• Single Supply Voltage (min): 900mV
• Single Supply Voltage (max): 2.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 10
• Package Type: MSOP
• Lead Free Status / Rohs Status: Not Compliant

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Application Information
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4916’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
allows 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
layout, fabrication, and mounting an LD (LLP) package is
available from National Semiconductor’s Package Engineer-
ing 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 em-
ploy a battery (or 1.5V regulator) with 10µF tantalum or
electrolytic capacitor and a ceramic bypass capacitor that
aid in supply stability. This does not eliminate the need for
bypassing the supply nodes of the LM4916. A bypass ca-
pacitor value in the range of 0.1µF to 1µF is recommended.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4916’s shutdown function. Activate micro-power shut-
down by applying a logic-low voltage to the SHUTDOWN
pin. When active, the LM4916’s micro-power shutdown fea-
ture turns off the amplifier’s bias circuitry, reducing the sup-
ply 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 0.02µA (typ) shutdown current is achieved by ap-
plying 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 microprocessor, or a mi-
crocontroller. When using a switch, connect an external
100kΩ pull-up resistor between the SHUTDOWN pin and
V
ground. Select normal amplifier operation by opening the
switch. Closing the switch connects the SHUTDOWN pin to
ground, activating micro-power shutdown. The switch and
resistor guarantee that the SHUTDOWN pin will not float.
This prevents unwanted state changes. In a system 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.
MUTE
When in single ended mode, the LM4916 also features a
mute function that enables extremely fast turn-on/turn-off
with a minimum of output pop and click with a low current
consumption (≤20µA, typical). The mute function leaves the
outputs at their bias level, thus resulting in higher power
consumption than shutdown mode, but also provides much
faster turn on/off times. Providing a logic low signal on the
MUTE pin enables mute mode. Threshold voltages and ac-
DD
. Connect the switch between the SHUTDOWN pin and
(Continued)
14
tivation techniques match those given for the shutdown func-
tion as well. Mute may not appear to function when the
LM4916 is used to drive high impedance loads. This is
because the LM4916 relies on a typical headphone load
(16-32Ω) to reduce input signal feed-through through the
input and feedback resistors. Mute attenuation can thus be
calculated by the following formula:
Parallel load resistance may be necessary to achieve satis-
factory mute levels when the application load is known to be
high impedance. The mute function, described above, is not
necessary when the LM4916 is operating in BTL mode since
the shutdown function operates quickly in BTL mode with
less power consumption than mute. In these modes, the
Mute signal is equivalent to the Shutdown signal. Mute may
be enabled during shutdown transitions, but should not be
toggled for a brief period immediately after exiting or entering
shutdown. These brief time periods are labeled X1 (time
after returning from shutdown) and X2 (time after entering
shutdown) and are shown in the timing diagram given in
Figure 5. X1 occurs immediately following a return from
shutdown (TWU) and lasts 40ms
part is placed in shutdown and the decay of the bias voltage
has occurred (2.2*250k*CB) and lasts for 100ms
timing of these transition periods relative to X1 and X2 is also
shown in Figure 5. While in single ended mode, mute should
not be toggled during these time periods, but may be toggled
during the shutdown transitions or any other time the part is
in normal operation. Failure to operate mute correctly may
result in much higher click and pop values or failure of the
device to mute at all.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical to optimize device
and system performance. While the LM4916 is tolerant of
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity. The LM4916 is unity-gain stable that gives the designer
maximum system flexibility. The LM4916 should be used in
low gain configurations to minimize THD+N values, and
maximize the signal to noise ratio. Low gain configurations
require large input signals to obtain a given output power.
Input signals equal to or greater than 1V
from sources such as audio codecs. Very large values
should not be used for the gain-setting resistors. Values for
R
section, Audio Power Amplifier Design, for a more complete
explanation of proper gain selection. Besides gain, one of
the major considerations is the closed-loop bandwidth of the
amplifier. To a large extent, the bandwidth is dictated by the
choice of external components shown in Figures 2 and 3.
The input coupling capacitor, C
filter that limits low frequency response. This value should be
chosen based on needed frequency response and turn-on
time.
SELECTION OF INPUT CAPACITOR SIZE
Amplifying the lowest audio frequencies requires a high
value input coupling capacitor, C
be expensive and may compromise space efficiency in por-
table designs. In many cases, however, the headphones
used in portable systems have little ability to reproduce
signals below 60Hz. Applications using headphones with this
i
Mute Attenuation (dB) = 20Log[R
and R
f
should be less than 1MΩ. Please refer to the
i
, forms a first order high pass
i
. A high value capacitor can
±
25%. X2 occurs after the
L
/ (R
i
+R
rms
F
)]
are available
±
25%. The