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參數資料
| 型號： | LM4863N/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDIP16 |
| 封裝： | 0.300 INCH, MDIP-16 |
| 文件頁數： | 5/21頁 |
| 文件大?。?/td> | 1219K |
| 代理商： | LM4863N/NOPB |
Application Information (Continued)
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):
P
DMAX’= (TJMAX TA)/
θ
JA
(4)
The LM4863’s T
JMAX = 150C. In the LQ (LLP) package
soldered to a DAP pad that expands to a copper area of 5in
2
on a PCB, the LM4863’s
θ
JA is 20C/W. In the MTE package
soldered to a DAP pad that expands to a copper area of 2in
2
on a PCB , the LM4863’s
θ
JA is 41C/W. At any given
ambient temperature T
J\A, use Equation (4) to find the maxi-
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.
T
A =TJMAX 2xPDMAX
θ
JA
(5)
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 99C for the LLP
package and 45C for the MTE package.
T
JMAX =PDMAX
θ
JA +TA
(6)
Equation (6) gives the maximum junction temperature T
J-
MAX
. If the result violates the LM4863’s 150C, reduce the
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
JA. The heat sink can be created using additional
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
JA is the sum of
θ
JC,
θ
CS, and
θ
SA.(
θ
JC is the
junctiontocase thermal impedance,
CS is the casetosink
thermal impedance, and
θ
SAis the sinktoambient thermal
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 10F in parallel with a 0.1F 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 1.0F
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
1F capacitor, C
B, between the BYPASS pin and ground
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
B, depends on desired PSRR require-
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
DD to the SHUTDOWN pin. When active,
the LM4863’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically V
DD/2. The low 0.7A typical
shutdown current is achieved by applying a voltage that is as
near as V
DD as possible to the SHUTDOWN pin. A voltage
thrat is less than V
DD 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 microcontroller. When using a switch,
connect an external 10k
pull-up resistor between the
SHUTDOWN pin and V
DD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V
DD through the pull-up resistor, activat-
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.
TABLE 1. Logic level truth table for SHUTDOWN and
HP-IN Operation
SHUTDOWN
HP-IN PIN
OPERATIONAL MODE
Low
logic Low
Bridged amplifiers
Low
logic High
Single-Ended amplifiers
High
logic Low
Micro-power Shutdown
High
logic High
Micro-power Shutdown
HP-IN FUNCTION
Applying a voltage between 4V and V
DD to the LM4863’s
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-
LM4863
www.national.com
13
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