LM4863MX National Semiconductor, LM4863MX Datasheet - Page 13

• Manufacturer Part Number: LM4863MX
• Description: Audio Amp Headphone/Speaker 2-CH Stereo 1.5W Class-AB 16-Pin SOIC W T/R
• Manufacturer: National Semiconductor

Specifications of LM4863MX

• Package: 16SOIC W
• Function: Headphone/Speaker
• Amplifier Type: Class-AB
• Total Harmonic Distortion Noise: 0.3@8Ohm@1W|0.2@32Ohm@75mW %
• Typical Psrr: 67 dB
• Output Signal Type: Differential|Single
• Output Type: 2-Channel Stereo
• Maximum Load Resistance: 32 Ohm

Application Information
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 LM4863’s T
soldered to a DAP pad that expands to a copper area of 5in
on a PCB, the LM4863’s θ
soldered to a DAP pad that expands to a copper area of 2in
on a PCB , the LM4863’s θ
ambient temperature T
mum internal power dissipation supported by the IC packag-
ing. Rearranging Equation (4) and substituting PDMAX for
PDMAX’ results in Equation (5). This equation gives the
maximum ambient temperature that still allows maximum
stereo power dissipation without violating the LM4863’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 LLP
package and 45˚C for the MTE package.
Equation (6) gives the maximum junction temperature T
MAX
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,
thermal impedance, and θ
impedance.) Refer to the Typical Performance Characteris-
tics curves for power dissipation information at lower output
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 10µF in parallel with a 0.1µF filter capacitors to stabi-
lize 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
LM4863’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation in the output signal. Keep the length of leads and
traces that connect capacitors between the LM4863’s power
supply pin and ground as short as possible. Connecting a
. If the result violates the LM4863’s 150˚C, reduce the
JA
. The heat sink can be created using additional
JA
T
P
A
JMAX
DMAX
T
is the sum of θ
= T
JMAX
JMAX
’ = (T
J\A
= 150˚C. In the LQ (LLP) package
= P
, use Equation (4) to find the maxi-
JA
SA
JMAX
− 2 x P
DMAX
is 20˚C/W. In the MTE package
is the sink−to−ambient thermal
JA
JC
− T
θ
is 41˚C/W. At any given
, θ
JA
DMAX
A
CS
+ T
CS
) / θ
, and θ
is the case−to−sink
θ
A
JA
JA
(Continued)
SA
. (θ
JC
is the
(4)
(5)
(6)
J -
2
2
13
1µF capacitor, C
improves the internal bias voltage’s stability and improves
the amplifier’s PSRR. The PSRR improvements increase as
the bypass pin capacitor value increases. Too large, how-
ever, increases turn-on time and can compromise 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.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4863’s shutdown function. Activate micro-power shut-
down by applying V
the LM4863’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
thrat is less than V
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 10kΩ pull-up resistor between the
SHUTDOWN pin and V
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V
ing micro-power shutdown. The switch and resistor guaran-
tee that the SHUTDOWN pin will not float. This prevents
unwanted state changes. In a system with a microprocessor
or a 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.
HP-IN FUNCTION
Applying a voltage between 4V and V
HP-IN headphone control pin turns off Amp2A and Amp2B,
muting a bridged-connected load. Quiescent current con-
sumption is reduced when the IC is in this single-ended
mode.
Figure 2 shows the implementation of the LM4863’s head-
phone control function. With no headphones connected to
the headphone jack, the R1-R2 voltage divider sets the
voltage applied to the HP-IN pin (pin 16) at approximately
50mV. This 50mV enables Amp1B and Amp2B, placing the
LM4863’s in bridged mode operation. The output coupling
capacitor blocks the amplifier’s half-supply DC voltage, pro-
tecting the headphones.
While the LM4863 operates in bridged mode, the DC poten-
tial across the load is essentially 0V. The HP-IN threshold is
set at 4V. Therefore, even in an ideal situation, the output
swing cannot cause a false single-ended trigger. Connecting
headphones to the headphone jack disconnects the head-
TABLE 1. Logic level truth table for SHUTDOWN and
SHUTDOWN
High
High
Low
Low
DD
as possible to the SHUTDOWN pin. A voltage
B
, between the BYPASS pin and ground
DD
DD
HP-IN PIN
logic High
logic High
HP-IN Operation
logic Low
logic Low
DD
may increase the shutdown current.
to the SHUTDOWN pin. When active,
B
DD
, depends on desired PSRR require-
through the pull-up resistor, activat-
. Connect the switch between the
DD
/2. The low 0.7µA typical
Single-Ended amplifiers
OPERATIONAL MODE
Micro-power Shutdown
Micro-power Shutdown
Bridged amplifiers
DD
to the LM4863’s
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