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参数资料
| 型号： | LM4913MH/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.09 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封装： | TSSOP-10 |
| 文件页数： | 3/18页 |
| 文件大小： | 1078K |
| 代理商： | LM4913MH/NOPB |
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions. The LM4913 has
two operational amplifiers driving a mono bridge load. The
maximum internal power dissipation operating in the bridge
mode is twice that of a single-ended amplifier. From Equation
(3), assuming a 5V power supply and an 8
load, the maxi-
mum BTL-mode power dissipation is 317mW.
P
DMAX-MONOBTL = 2(VDD)
2
/ 2
π2R
L:
Bridge Mode
(3)
The maximum power dissipation point given by Equation (3)
must not exceed the power dissipation given by Equation (4):
P
DMAX = (TJMAX - TA) / θJA
(4)
The LM4913's TJMAX = 150°C. In the MH package, the
LM4913's
θ
JA is 46°C/W. At any given ambient temperature
TA, use Equation (4) to find the maximum internal power dis-
sipation supported by the IC packaging. Rearranging Equa-
tion (4) and substituting PDMAX for PDMAX ' results in
Equation (5). This equation gives the maximum ambient tem-
perature that still allows maximum mono BTL power dissipa-
tion without violating the LM4913's maximum junction tem-
perature.
T
A = TJMAX - PDMAX-MONOBTLθJA
(5)
For a typical application with a 5V power supply and an 8
load, the maximum ambient temperature that allows maxi-
mum BTL power dissipation without exceeding the maximum
junction temperature is approximately 134°C for the IBL pack-
age.
T
JMAX = PDMAX-MONOBTLθJA + TA
(6)
Equation (6) gives the maximum junction temperature
T
JMAX. If the result violates the LM4913's 150°C TJMAX, reduce
the maximum junction temperature by decreasing the power
supply voltage or increasing the load resistance. Further al-
lowance should be made for increased ambient tempera-
tures.
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 (3) is greater
than that of Equation (4), then decrease the supply voltage,
increase the load impedance, or reduce the ambient temper-
ature. If these measures are insufficient, a heat sink can be
added to reduce
θ
JA. The heat sink can be created using ad-
ditional copper area around the package, with connections to
the ground pin(s), supply pin and amplifier output pins. Ex-
ternal, 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 θJC, θCS, and θSA. (θJC is the
junction-to-case thermal impedance,
θ
CS is the case-to-sink
thermal impedance, and
θ
SA is the sink-to-ambient thermal
impedance.) Refer to the Typical Performance Characteris-
tics curves for power dissipation information at lower output
power levels.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4913's exposed-DAP (die attach paddle) package
provides a low thermal resistance between the die and the
PCB to which the part is mounted and soldered. This low
thermal resistance is achieved by soldering the DAP to a cop-
per pad on the PCB. The copper pad's dimensions should
match the DAP's. The copper pad should then connect to a
larger copper area. This area can be on the component side,
in an inner layer in a multi-layer board, or on the board's back
side. This connection from the DAP, to the DAP pad, and fi-
nally to a larger copper area allows rapid heat transfer away
from the die to the surrounding air. The result is a low voltage
audio power amplifier that produces 2.0W at =1% THD+N
with a 4
load. This high power is achieved through careful
consideration of necessary thermal design. Failing to opti-
mize thermal design may compromise the LM4913's high
power performance and activate unwanted, though neces-
sary, thermal shutdown protection.
The MH package must have its DAP soldered to a copper pad
on the PCB. The DAP's PCB copper pad is connected to a
large plane of continuous unbroken copper. This plane forms
a thermal mass, and heat sink, and radiation area. Place the
heat sink area on either outside plane in the case of a two-
sided PCB, or on an inner layer of a board with more than two
layers. Connecting to a ground plane is permissible. Connect
the DAP copper pad to the inner layer or backside copper heat
sink area with 4(2x2) vias. The via diameter should be
0.012in-0.013in with a 1.27mm pitch. Ensure efficient thermal
conductivity by plating-through and solder-filling the vias.
Best thermal performance is achieved with the largest prac-
tical copper heatsink area. If the heatsink and amplifier share
the same PCB layer, a nominal 2.5in2 (min) area is necessary
for 5V operation with a 4
load. The heatsink area should be
5in2 (min) when placed on a layer different from that used by
the LM4913. The last two area recommendations apply for
25°C ambient temperature. Increase the area to compensate
for ambient temperatures above 25°C. In all circumstances
and conditions, the junction temperature must be held below
150°C to prevent activating the LM4913's thermal shutdown
protection. The LM4913's power de-rating curve in the Typical
Performance Characteristics shows the maximum power dis-
sipation versus temperature. An example PCB layout for the
LM4913's exposed-DAP package is shown in the Demon-
stration Board Layout section.
PCB LAYOUT AND SUPPLY REGULATION
CONSIDERATIONS FOR DRIVING 4
LOADS
Power dissipated by a load is a function of the voltage swing
across the load and the load's impedance. As load impedance
decreases, load dissipation becomes increasingly dependent
on the interconnect (PCB trace and wire) resistance between
the amplifier output pins and the load's connections. Residual
trace resistance causes a voltage drop, which results in power
dissipated in the trace and not in the load as desired. For ex-
ample, 0.1
trace resistance reduces the output power dis-
sipated by a 4
load from 2W to 1.9W. This problem of
decreased load dissipation is exacerbated as load impedance
decreases. Therefore, to maintain the highest load dissipation
and widest output voltage swing, PCB traces that connect the
output pins to a load must be as wide as possible.
Poor power supply regulation adversely affects maximum
output power. A poorly regulated supply's output voltage de-
creases with increasing load current. Reduced supply voltage
causes decreased headroom, output signal clipping, and re-
duced output power. Even with tightly regulated supplies,
trace resistance creates the same effects as poor supply reg-
ulation. Therefore, make the power supply traces as wide as
possible to maintain full output voltage swing.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is crit-
ical for low noise performance and high power supply rejec-
tion. Applications that employ a 5V regulator typically use a
10F in parallel with a 0.1F filter capacitors to stabilize the
11
www.national.com
LM4913
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