LM4907LQ [NSC]
1 Watt Audio Power Amplifier; 1瓦音频功率放大器
| 型号： | LM4907LQ |
| 厂家： | 
National Semiconductor |
| 描述： | 1 Watt Audio Power Amplifier |
| 文件： | 总17页 (文件大小：1060K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
April 2005
LM4907
1 Watt Audio Power Amplifier
General Description
Key Specifications
The LM4907 is an audio power amplifier primarily designed
for demanding applications in mobile phones and other por-
table communication device applications. It is capable of
delivering 1 Watt of continuous average power to an 8Ω BTL
load with less than 1% distortion (THD+N) from a 5VDC
power supply.
j
j
j
j
Improved PSRR at 217Hz & 1KHz
62dB
Power Output at 5.0V, 1% THD+N, 8Ω
1.0W (typ)
Power Output at 3.0V, 1% THD+N, 8Ω 390mW (typ)
Shutdown Current 0.1µA (typ)
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4907 does not require output
coupling capacitors or bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage appli-
cations where minimal power consumption is a primary re-
quirement.
Features
n Available in space-saving LLP package
n Ultra low current shutdown mode
n BTL output can drive capacitive loads
n Improved pop & click circuitry eliminates noise during
turn-on and turn-off transitions
The LM4907 features a low-power consumption shutdown
mode which is achieved by driving the shutdown pin with
logic low. Additionally, the LM4907 features an internal ther-
mal shutdown protection mechanism.
n 2.2 - 5.5V operation
n No output coupling capacitors, snubber networks or
bootstrap capacitors required
n Unity-gain stable
n External gain configuration capability
The LM4907 contains advanced pop & click circuitry which
eliminates noise which would otherwise occur during turn-on
and turn-off transitions.
Applications
n Mobile Phones
n PDAs
The LM4907 is unity-gain stable and can be configured by
external gain-setting resistors.
n Portable electronic devices
Typical Application
200870D3
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation
DS200870
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Connection Diagrams
LQ Package
20087003
Top View
Order Number LM4907LQ
See NS Package Number LQB08A
LQ Package Marking
20087004
Top View
X = One Digit Date Code
TT = Lot Traceability
G = Boomer
A9 = LM4907LQ
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2
Absolute Maximum Ratings (Note 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Junction Temperature
Thermal Resistance
θJC (LQ)
150˚C
57˚C/W
θJA (LQ)
140˚C/W
Supply Voltage (Note 10)
Storage Temperature
6.0V
−65˚C to +150˚C
−0.3V to VDD +0.3V
Internally Limited
2000V
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage
Input Voltage
Power Dissipation (Notes 3, 11)
ESD Susceptibility (Note 4)
ESD Susceptibility (Note 5)
−40˚C ≤ TA ≤ 85˚C
2.2V ≤ VDD ≤ 5.5V
200V
Electrical Characteristics VDD = 5V (Notes 1, 2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C.
LM4907
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Notes 7, 8)
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VGND
3.4
7
10
2
mA (max)
mA (max)
µA (max)
V
IDD
Quiescent Power Supply Current
4
ISD
Shutdown Current
0.8
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
Output Power
1.5
1.3
V
7
1.07
50
mV (max)
W (min)
ms
Po
THD = 1% (max); f = 1 kHz
0.9
TWU
THD+N
Wake-up time
100
Total Harmonic Distortion+Noise
Po = 0.5 Wrms; f = 1kHz
Vripple = 200mV sine p-p
Input terminated with 10Ω
0.2
%
60 (f = 217Hz)
64 (f = 1kHz)
PSRR
Power Supply Rejection Ratio
55
dB (min)
Electrical Characteristics VDD = 3V (Notes 1, 2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C.
LM4907
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Notes 7, 8)
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VGND
2.4
7
9
mA (max)
IDD
Quiescent Power Supply Current
3
mA (max)
ISD
Shutdown Current
0.1
1.0
µA (max)
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
Output Power
1.3
V
1.0
V
mV (max)
mW
7
390
50
55
Po
THD = 1% (max); f = 1 kHz
TWU
THD+N
Wake-up time
75
ms
Total Harmonic Distortion+Noise
Po = 0.25 Wrms; f = 1kHz
Vripple = 200mV sine p-p
Input terminated with 10Ω
0.1
%
65 (f = 217Hz)
70 (f = 1kHz)
PSRR
Power Supply Rejection Ratio
dB (min)
3
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Electrical Characteristics VDD = 2.6V (Notes 1, 2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C.
LM4907
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Notes 7, 8)
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VGND
2.0
mA
IDD
Quiescent Power Supply Current
3.0
mA
ISD
Shutdown Current
0.01
1.0
50
µA (max)
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
Output Power
1.2
V
1.0
V
mV (max)
mW
5
270
Po
THD = 1% (max); f = 1 kHz
TWU
THD+N
Wake-up time
70
ms
Total Harmonic Distortion + Noise
Po = 0.15 Wrms; f = 1kHz
Vripple = 200mV sine p-p
Input terminated with 10Ω
0.1
%
51 (f = 217Hz)
51 (f = 1kHz)
PSRR
Power Supply Rejection Ratio
dB
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
, θ , and the ambient temperature T . The maximum
A
JMAX JA
allowable power dissipation is P
= (T
–T )/θ or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4907, see power derating
DMAX
JMAX A JA
curves for additional information.
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 5: Machine Model, 220pF–240pF discharged through all pins.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 9: R
is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the two 20kΩ resistors.
OUT
Note 10: If the product is in Shutdown mode and V exceeds 6V (to a max of 8V V ), then most of the excess current will flow through the ESD protection circuits.
DD
DD
If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is enabled when V is greater than 5.5V and less than
DD
6.5V, no damage will occur, although operation life will be reduced. Operation above 6.5V with no current limit will result in permanent damage.
Note 11: Maximum power dissipation in the device (P
) occurs at an output power level significantly below full output power. P
can be calculated using
DMAX
DMAX
Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs.
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External Components Description
(Figure 1)
Components
Functional Description
1.
Ri
Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a
high pass filter with Ci at fC= 1/(2π RiCi).
2.
Ci
Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a
highpass filter with Ri at fc = 1/(2π RiCi). Refer to the section, Proper Selection of External Components,
for an explanation of how to determine the value of Ci.
3.
4.
Rf
Feedback resistance which sets the closed-loop gain in conjunction with Ri.
CS
Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing
section for information concerning proper placement and selection of the supply bypass capacitor.
Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External
Components, for information concerning proper placement and selection of CB.
5.
CB
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Frequency
at VDD = 5V, 8Ω RL, and PWR = 500mW
at VDD = 3V, 8Ω RL, and PWR = 250mW
20087030
20087031
THD+N vs Frequency
THD+N vs Power Out
at VDD = 2.6V, 8Ω RL, and PWR = 150mW
at VDD = 5V, 8Ω RL, 1kHz
20087032
20087034
5
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Typical Performance Characteristics (Continued)
THD+N vs Power Out
THD+N vs Power Out
at VDD = 3V, 8Ω RL, 1kHz
at VDD = 2.6V, 8Ω RL, 1kHz
20087083
20087084
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
at VDD = 5V, 8Ω RL
at VDD = 5V, 8Ω RL
20087086
20087087
Input terminated with 10Ω
Input Floating
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
at VDD = 3V, 8Ω RL
at VDD = 3V, 8Ω RL
20087088
20087089
Input terminated with 10Ω
Input Floating
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Typical Performance Characteristics (Continued)
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
at VDD = 2.6V, 8Ω RL
at VDD = 2.6V, 8Ω RL
20087090
20087091
Input terminated with 10Ω
Input Floating
Open Loop Frequency Response, 5V
Open Loop Frequency Response, 3V
20087092
20087093
Open Loop Frequency Response, 2.6V
Noise Floor, 5V, 8Ω
80kHz Bandwidth, Input to GND
20087094
20087095
7
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Typical Performance Characteristics (Continued)
Power Derating Curves
Power Dissipation vs
Output Power, 5V, 8Ω
20087069
20087097
Power Dissipation vs
Output Power, VDD=3V
Power Dissipation vs
Output Power, VDD=2.6V
200870C8
200870C9
Shutdown Hysteresis Voltage
5V
Shutdown Hysteresis Voltage
3V
200870A1
200870A3
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Typical Performance Characteristics (Continued)
Shutdown Hysteresis Voltage
2.6V
Output Power vs
Supply Voltage, 8Ω
200870A5
200870A6
Output Power vs
Output Power vs
Supply Voltage, 16Ω
Supply Voltage, 32Ω
200870A7
200870A8
Frequency Response vs
Input Capacitor Size
20087054
9
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Application Information
BRIDGE CONFIGURATION EXPLANATION
output pins. Refer to the application information on the
LM4907 reference design board for an example of good heat
sinking. If TJMAX still exceeds 150˚C, then additional
changes must be made. These changes can include re-
duced supply voltage, higher load impedance, or reduced
ambient temperature. Internal power dissipation is a function
of output power. Refer to the Typical Performance Charac-
teristics curves for power dissipation information for differ-
ent output powers and output loading.
As shown in Figure 1, the LM4907 has two internal opera-
tional amplifiers. The first amplifier’s gain is externally con-
figurable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of Rf to Ri while
the second amplifier’s gain is fixed by the two internal 20kΩ
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both
amplifiers producing signals identical in magnitude, but out
of phase by 180˚. Consequently, the differential gain for the
IC is
EXPOSED-DAP MOUNTING CONSIDERATIONS
The LM4907’s exposed-DAP (die attach paddle) packages
(LD) provide 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 area heatsink, copper traces, ground plane, and
finally, surrounding air. The result is a low voltage audio
power amplifier that produces 1.07W dissipation in an 8Ω
load at ≤ 1% THD+N. This power is achieved through careful
consideration of necessary thermal design. Failing to opti-
mize thermal design may compromise the LM4907’s perfor-
mance and activate unwanted, though necessary, thermal
shutdown protection.
AVD= 2 *(Rf/Ri)
By driving the load differentially through outputs Vo1 and
Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classical single-ended amplifier configura-
tion where one side of the load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential
drive to the load, thus doubling output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same con-
ditions. This increase in attainable output power assumes
that the amplifier is not current limited or clipped. In order to
choose an amplifier’s closed-loop gain without causing ex-
cessive clipping, please refer to the Audio Power Amplifier
Design section.
The LM4907LD must have its DAP soldered to a copper pad
on the PCB. The DAP’s PCB copper pad is then, ideally,
connected to a large plane of continuous unbroken copper.
This plane forms a thermal mass, heat sink, and radiation
area. Place the heat sink area on either outside plane in the
case of a two-sided or multi-layer PCB. (The heat sink area
can also be placed on an inner layer of a multi-layer board.
The thermal resistance, however, will be higher.) Connect
the DAP copper pad to the inner layer or backside copper
heat sink area with 2 vias. The via diameter should be
0.012in - 0.013in with a 1.27mm pitch. Ensure efficient ther-
mal conductivity by plugging and tenting the vias with plating
and solder mask, respectively.
A bridge configuration, such as the one used in LM4907,
also creates a second advantage over single-ended amplifi-
ers. Since the differential outputs, Vo1 and Vo2, are biased
at half-supply, no net DC voltage exists across the load. This
eliminates the need for an output coupling capacitor which is
required in a single supply, single-ended amplifier configura-
tion. Without an output coupling capacitor, the half-supply
bias across the load would result in both increased internal
IC power dissipation and also possible loudspeaker damage.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for
low noise performance and high power supply rejection. The
capacitor location on both the bypass and power supply pins
should be as close to the device as possible. Typical appli-
cations employ a 5V regulator with 10 µF tantalum or elec-
trolytic capacitor and a ceramic bypass capacitor which aid
in supply stability. This does not eliminate the need for
bypassing the supply nodes of the LM4907. The selection of
a bypass capacitor, especially CB, is dependent upon PSRR
requirements, click and pop performance (as explained in
the section, Proper Selection of External Components),
system cost, and size constraints.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation. Since the LM4907 has two opera-
tional amplifiers in one package, the maximum internal
power dissipation is 4 times that of a single-ended amplifier.
The maximum power dissipation for a given application can
be derived from the power dissipation graphs or from Equa-
tion 1.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4907 contains shutdown circuitry that is used to turn off
the amplifier’s bias circuitry. This shutdown feature turns the
amplifier off when logic low is placed on the shutdown pin.
By switching the shutdown pin to GND, the LM4907 supply
current draw will be minimized in idle mode. Idle current is
measured with the shutdown pin connected to GND. The
trigger point for shutdown is shown as a typical value in the
Shutdown Hysteresis Voltage graphs in the Typical Perfor-
mance Characteristics section. It is best to switch between
ground and supply for maximum performance. While the
device may be disabled with shutdown voltages in between
ground and supply, the idle current may be greater than the
PDMAX = 4*(VDD)2/(2π2RL)
(1)
It is critical that the maximum junction temperature TJMAX of
150˚C is not exceeded. TJMAX can be determined from the
power derating curves by using PDMAX and the PC board foil
area. By adding copper foil, the thermal resistance of the
application can be reduced from the free air value of θJA
,
resulting in higher PDMAX values without thermal shutdown
protection circuitry being activated. Additional copper foil can
be added to any of the leads connected to the LM4907. It is
especially effective when connected to VDD, GND, and the
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10
C
B equal to 0.1µF, the device will be much more susceptible
Application Information (Continued)
typical value of 0.1µA. In either case, the shutdown pin
should be tied to a definite voltage to avoid unwanted state
changes.
to turn-on clicks and pops. Thus, a value of CB equal to
1.0µF is recommended in all but the most cost sensitive
designs.
AUDIO POWER AMPLIFIER DESIGN
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry, which pro-
vides a quick, smooth transition to shutdown. Another solu-
tion is to use a single-throw switch in conjunction with an
external pull-up resistor. This scheme guarantees that the
shutdown pin will not float, thus preventing unwanted state
changes.
A 1W/8Ω Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
1 Wrms
8Ω
1 Vrms
Input Impedance
Bandwidth
20 kΩ
PROPER SELECTION OF EXTERNAL COMPONENTS
100 Hz–20 kHz 0.25 dB
Proper selection of external components in applications us-
ing integrated power amplifiers is critical to optimize device
and system performance. While the LM4907 is tolerant of
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity.
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics section, the supply rail can be
easily found.
The LM4907 is unity-gain stable which gives the designer
maximum system flexibility. The LM4907 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 1 Vrms are available
from sources such as audio codecs. Please refer to the
section, Audio Power Amplifier Design, for a more com-
plete explanation of proper gain selection.
5V is a standard voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4907 to reproduce peaks in excess of 1W
without producing audible distortion. At this time, the de-
signer must make sure that the power supply choice along
with the output impedance does not violate the conditions
explained in the Power Dissipation section.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 2.
Besides gain, one of the major considerations is the closed-
loop bandwidth of the amplifier. To a large extent, the band-
width is dictated by the choice of external components
shown in Figure 1. The input coupling capacitor, Ci, forms a
first order high pass filter which limits low frequency re-
sponse. This value should be chosen based on needed
frequency response for a few distinct reasons.
(2)
Rf/Ri = AVD/2
From Equation 2, the minimum AVD is 2.83; use AVD = 3.
Selection Of Input Capacitor Size
Since the desired input impedance was 20 kΩ, and with a
AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results in an
allocation of Ri = 20 kΩ and Rf = 30 kΩ. The final design step
is to address the bandwidth requirements which must be
stated as a pair of −3 dB frequency points. Five times away
from a −3 dB point is 0.17 dB down from passband response
which is better than the required 0.25 dB specified.
Large input capacitors are both expensive and space hungry
for portable designs. Clearly, a certain sized capacitor is
needed to couple in low frequencies without severe attenu-
ation. But in many cases the speakers used in portable
systems, whether internal or external, have little ability to
reproduce signals below 100Hz to 150Hz. Thus, using a
large input capacitor may not increase actual system perfor-
mance.
fL = 100 Hz/5 = 20 Hz
fH = 20 kHz * 5 = 100 kHz
In addition to system cost and size, click and pop perfor-
mance is effected by the size of the input coupling capacitor,
Ci. A larger input coupling capacitor requires more charge to
reach its quiescent DC voltage (nominally 1/2 VDD). This
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the
capacitor size based on necessary low frequency response,
turn-on pops can be minimized.
As stated in the External Components section, Ri in con-
junction with Ci create a highpass filter.
Ci ≥ 1/(2π*20 kΩ*20 Hz) = 0.397 µF; use 0.39 µF
The high frequency pole is determined by the product of the
desired frequency pole, fH, and the differential gain, AVD
.
With a AVD = 3 and fH = 100 kHz, the resulting GBWP =
300kHz which is much smaller than the LM4907 GBWP of
2.5MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4907 can still be used without running into bandwidth
limitations.
Besides minimizing the input capacitor size, careful consid-
eration should be paid to the bypass capacitor value. Bypass
capacitor, CB, is the most critical component to minimize
turn-on pops since it determines how fast the LM4907 turns
on. The slower the LM4907’s outputs ramp to their quiescent
DC voltage (nominally 1/2 VDD), the smaller the turn-on pop.
Choosing CB equal to 1.0µF along with a small value of Ci (in
the range of 0.1µF to 0.39µF), should produce a virtually
clickless and popless shutdown function. While the device
will function properly, (no oscillations or motorboating), with
The LM4907 is unity-gain stable and requires no external
components besides gain-setting resistors, an input coupling
capacitor, and proper supply bypassing in the typical appli-
cation. However, if a closed-loop differential gain of greater
than 10 is required, a feedback capacitor (C4) may be
needed as shown in Figure 2 to bandwidth limit the amplifier.
This feedback capacitor creates a low pass filter that elimi-
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20kHz. A typical combination of feedback resistor and ca-
pacitor that will not produce audio band high frequency rolloff
is R3 = 20kΩ and C4 = 25pf. These components result in a
-3dB point of approximately 320 kHz.
Application Information (Continued)
nates possible high frequency oscillations. Care should be
taken when calculating the -3dB frequency in that an incor-
rect combination of R3 and C4 will cause rolloff before
200870D4
FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER
200870D5
FIGURE 3. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4907
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Application Information (Continued)
200870D6
FIGURE 4. REFERENCE DESIGN BOARD SCHEMATIC
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Application Information (Continued)
LM4907 MSOP BOARD ARTWORK
Composite View
Silk Screen
200870E4
200870E3
Top Layer
Bottom Layer
200870E5
200870E2
MONO LM4907 REFERENCE DESIGN BOARDS
BILL OF MATERIAL
Part Description
Quantity
Reference Designator
LM4907 Audio AMP
1
2
1
2
1
U1
Tantalum Capcitor, 1µF
Ceramic Capacitor, 0.39µF
Resistor, 20kΩ, 1/10W
Resistor, 100kΩ, 1/10W
C1, C3
C2
R2, R3
R1
Jumper Header Vertical Mount 2X1 0.100“ spacing
1
J1
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Single-Point Power / Ground Connections
Application Information (Continued)
PCB LAYOUT GUIDELINES
The analog power traces should be connected to the digital
traces through a single point (link). A "Pi-filter" can be helpful
in minimizing High Frequency noise coupling between the
analog and digital sections. It is further recommended to put
digital and analog power traces over the corresponding digi-
tal and analog ground traces to minimize noise coupling.
This section provides practical guidelines for mixed signal
PCB layout that involves various digital/analog power and
ground traces. Designers should note that these are only
"rule-of-thumb" recommendations and the actual results will
depend heavily on the final layout.
Placement of Digital and Analog Components
GENERAL MIXED SIGNAL LAYOUT
RECOMMENDATION
All digital components and high-speed digital signal traces
should be located as far away as possible from analog
components and circuit traces.
Power and Ground Circuits
For 2 layer mixed signal design, it is important to isolate the
digital power and ground trace paths from the analog power
and ground trace paths. Star trace routing techniques (bring-
ing individual traces back to a central point rather than daisy
chaining traces together in a serial manner) can have a
major impact on low level signal performance. Star trace
routing refers to using individual traces to feed power and
ground to each circuit or even device. This technique will
require a greater amount of design time but will not increase
the final price of the board. The only extra parts required will
be some jumpers.
Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces
parallel to each other (side-by-side) on the same PCB layer.
When traces must cross over each other do it at 90 degrees.
Running digital and analog traces at 90 degrees to each
other from the top to the bottom side as much as possible will
minimize capacitive noise coupling and cross talk.
15
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Physical Dimensions inches (millimeters) unless otherwise noted
LLP Package
Order Number LM4907LD
NS Package Number LDA08A
LLP Package
Order Number LM4907LQ
NS Package Number LQB08A
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16
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
MSOP Package
Order Number LM4907MM
NS Package Number MUA08A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
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Mono Class AB Audio Subsystem with a True Ground Headphone Amplifier and Earpiece Switch
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