LM4901MM [NSC]
1.6 Watt Audio Power Amplifier with Selectable Shutdown Logic Level; 1.6瓦音频功率放大器可选关断逻辑电平
| 型号： | LM4901MM |
| 厂家： | 
National Semiconductor |
| 描述： | 1.6 Watt Audio Power Amplifier with Selectable Shutdown Logic Level |
| 文件： | 总24页 (文件大小：1178K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
December 2002
LM4901
1.6 Watt Audio Power Amplifier with Selectable
Shutdown Logic Level
General Description
Key Specifications
The LM4901 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 and 1.6 watts of continuous avearge power to a 4Ω BTL
load with less than 1% distortion (THD+N) from a 5VDC
power supply.
j
j
j
j
j
j
Improved PSRR at 217Hz & 1KHz
Power Output at 5.0V, 1% THD, 4Ω
Power Output at 5.0V, 1% THD, 8Ω
Power Output at 3.0V, 1% THD, 4Ω
Power Output at 3.0V, 1% THD, 8Ω
Shutdown Current
62dB
1.6W (typ)
1.07W (typ)
525mW (typ)
390mW (typ)
0.1µA (typ)
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4901 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 packages: LLP, micro SMD,
and MSOP
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
n 2.0 - 5.5V operation
n No output coupling capacitors, snubber networks or
bootstrap capacitors required
n Unity-gain stable
n External gain configuration capability
n User selectable shutdown High or Low logic Level
The LM4901 features a low-power consumption shutdown
mode. To facilitate this, Shutdown may be enabled by either
logic high or low depending on mode selection. Driving the
shutdown mode pin either high or low enables the shutdown
pin to be driven in a likewise manner to enable shutdown.
The LM4901 contains advanced pop & click circuitry which
eliminates noise which would otherwise occur during turn-on
and turn-off transitions.
The LM4901 is unity-gain stable and can be configured by
external gain-setting resistors.
Applications
n Mobile Phones
n PDAs
n Portable electronic devices
Typical Application
20019801
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2002 National Semiconductor Corporation
DS200198
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Connection Diagrams
9 Bump micro SMD
Mini Small Outline (MSOP) Package
20019823
20019836
Top View
Top View
Order Number LM4901IBL, LM4901IBLX
See NS Package Number BLA09AAC
Order Number LM4901MM
See NS Package Number MUB10A
LLP Package
micro SMD Marking
20019870
Top View
X - Date Code
T - Die Traceability
G - Boomer Family
Q - LM4901IBL
200198B3
Top View
Order Number LM4901LD
See NS Package Number LDA10B
MSOP Marking
LLP Marking
20019871
Top View
200198B4
Top View
G - Boomer Family
C1 - LM4901MM
Z - Plant Code
XY - Date Code
TT - Die Traceability
Bottom Line - Part Number
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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.
θJA (MSOP)
θJA (LLP)
190˚C/W
63˚C/W (Note 14)
12˚C/W (Note 14)
θJC (LLP)
Soldering Information
Supply Voltage (Note 11)
Storage Temperature
Input Voltage
6.0V
−65˚C to +150˚C
−0.3V to VDD +0.3V
Internally Limited
2000V
See AN-1112 "microSMD Wafers Level Chip Scale
Package."
See AN-1187 "Leadless
Power Dissipation (Notes 3, 13)
ESD Susceptibility (Note 4)
ESD Susceptibility (Note 5)
Junction Temperature
Thermal Resistance
Leadframe Package (LLP)."
200V
Operating Ratings
Temperature Range
150˚C
TMIN ≤ TA ≤ TMAX
−40˚C ≤ TA ≤ 85˚C
2.0V ≤ VDD ≤ 5.5V
θJA (micro SMD) (Note 12)
θJC (MSOP)
180˚C/W
56˚C/W
Supply Voltage
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.
LM4901
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Notes 7, 9)
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VSD Mode (Note 8)
VSD MODE = VDD
3
7
mA (max)
mA (max)
µA (max)
V (min)
V (max)
V (min)
V (max)
mV (max)
kΩ (max)
kΩ (min)
W (min)
W
IDD
Quiescent Power Supply Current
4
10
2.0
ISD
Shutdown Current
0.1
1.5
1.3
1.5
1.3
7
VSDIH
VSDIL
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
VSD MODE = VDD
VSD MODE = GND
VSD MODE = GND
50
9.7
7.0
0.9
ROUT
Resistor Output to GND (Note 10)
8.5
Output Power (8Ω)
THD = 1% (max); f = 1 kHz
1.07
1.6
Po
(4Ω) (Notes 14, 15) THD = 1% (max); f = 1 kHz
TWU
Wake-up time
100
0.2
mS (max)
%
THD+N
Total Harmonic Distortion+Noise
Power Supply Rejection Ratio
Po = 0.5 Wrms; f = 1kHz
Vripple = 200mV sine p-p
Input terminated with 10Ω
60 (f =
PSRR
217Hz)
55
dB (min)
64 (f = 1kHz)
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.
LM4901
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Notes 7, 9)
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VSD Mode (Note 8)
VSD MODE = VDD
2
7
9
mA (max)
mA (max)
µA (max)
V (min)
IDD
Quiescent Power Supply Current
3
ISD
Shutdown Current
0.1
1.1
0.9
1.3
1.0
7
2.0
VSDIH
VSDIL
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
VSD MODE = VDD
V (max)
V (min)
VSD MODE = GND
VSD MODE = GND
V (max)
mV (max)
50
3
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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. (Continued)
=
LM4901
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Notes 7, 9)
9.7
(Note 6)
ROUT
kΩ (max)
kΩ (min)
mW
Resistor Output to GND (Note 10)
8.5
7.0
Output Power (8Ω)
(4Ω)
THD = 1% (max); f = 1 kHz
THD = 1% (max); f = 1 kHz
390
525
75
Po
mW
TWU
Wake-up time
mS (max)
%
THD+N
Total Harmonic Distortion+Noise
Po = 0.25 Wrms; f = 1kHz
Vripple = 200mV sine p-p
Input terminated with 10Ω
0.1
62 (f =
PSRR
Power Supply Rejection Ratio
217Hz)
55
dB (min)
68 (f = 1kHz)
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.
LM4901
Units
(Limits)
Symbol
Parameter
Conditions
Typical
(Note 6)
2.0
Limit
(Notes 7, 9)
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VSD Mode (Note 8)
VSD MODE = VDD
mA (max)
mA (max)
µA (max)
V (min)
IDD
Quiescent Power Supply Current
3.0
ISD
Shutdown Current
0.1
VSDIH
VSDIL
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
1.0
VSD MODE = VDD
0.9
V (max)
V (min)
VSD MODE = GND
1.2
VSD MODE = GND
1.0
V (max)
mV (max)
kΩ (max)
kΩ (min)
5
50
9.7
7.0
ROUT
Resistor Output to GND (Note 10)
8.5
Po
Output Power ( 8Ω )
( 4Ω )
THD = 1% (max); f = 1 kHz
THD = 1% (max); f = 1 kHz
275
340
70
mW
TWU
Wake-up time
mS (max)
%
THD+N
Total Harmonic Distortion+Noise
Po = 0.15 Wrms; f = 1kHz
Vripple = 200mV sine p-p
Input terminated with 10Ω
0.1
51 (f =
PSRR
Power Supply Rejection Ratio
217Hz)
dB (min)
51 (f = 1kHz)
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 LM4901, see power derating
DMAX
JMAX A JA
curves for additional information.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Machine Model, 220 pF–240 pF 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: For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase I by a maximum of 2µA.
SD
Note 9: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 10: 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.
ROUT
Note 11: 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.
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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. (Continued)
=
Note 12: All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. The LM4901IBL demo board (views featured
in the Application Information section) has two inner layers, one for V and one for GND. The planes each measure 611mils x 661mils (15.52mm x 16.79mm)
DD
and aid in spreading heat due to power dissipation within the IC.
Note 13: 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.
Note 14: The Exposed-DAP of the LDA10B package should be electrically connected to GND or an electrically isolated copper area. the LM4901LD demo board
(views featured in the Application Information section) has the Exposed-DAP connected to GND with a PCB area of 86.7mils x 585mils (2.02mm x 14.86mm) on
the copper top layer and 550mils x 710mils (13.97mm x 18.03mm) on the copper bottom layer.
Note 15: The thermal performance of the LLP package (LM4901LD) when used with the exposed-DAP connected to a thermal plane is sufficient for driving 4Ω
loads. The LM4901LD demo board (views featured in the Application Information section) can drive 4Ω loads at the maximum power dissipation point (1.267W)
without thermal shutdown circuitry being activated. The other available packages (MSOP & micro SMD) do not have the thermal performance necessary for driving
4Ω loads with a 5V supply and are not recommended for this application.
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
20019830
20019831
5
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Typical Performance Characteristics (Continued)
THD+N vs Frequency
THD+N vs Frequency
at VDD = 2.6V, 8Ω RL, and PWR = 150mW
at VDD = 2.6V, 4Ω RL, and PWR = 150mW
20019832
20019833
THD+N vs Power Out
THD+N vs Power Out
at VDD = 5V, 8Ω RL, 1kHz
at VDD = 3V, 8Ω RL, 1kHz
20019834
20019883
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Typical Performance Characteristics (Continued)
THD+N vs Power Out
THD+N vs Power Out
at VDD = 2.6V, 8Ω RL, 1kHz
at VDD = 2.6V, 4Ω RL, 1kHz
20019884
20019885
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
at VDD = 5V, 8Ω RL
at VDD = 5V, 8Ω RL
20019886
20019887
Input terminated with 10Ω
Input Floating
7
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Typical Performance Characteristics (Continued)
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
at VDD = 3V, 8Ω RL
at VDD = 3V, 8Ω RL
20019888
20019889
Input terminated with 10Ω
Input Floating
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
20019890
20019891
Input terminated with 10Ω
Input Floating
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Typical Performance Characteristics (Continued)
Open Loop Frequency Response, 5V
Open Loop Frequency Response, 3V
20019892
20019893
Noise Floor, 5V, 8Ω
80kHz Bandwidth, Input to GND
Open Loop Frequency Response, 2.6V
20019894
20019895
Power Derating Curves
Power Dissipation vs
Output Power, VDD=5V
20019869
200198B5
9
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Typical Performance Characteristics (Continued)
Power Dissipation vs
Output Power, VDD=3V
Power Dissipation vs
Output Power, VDD=2.6V
200198B6
200198B7
Shutdown Hysteresis Voltage
5V, SD Mode = VDD (High)
Shutdown Hysteresis Voltage
5V, SD Mode = GND (Low)
200198A0
200198A1
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Typical Performance Characteristics (Continued)
Shutdown Hysteresis Voltage
3V, SD Mode = VDD (High)
Shutdown Hysteresis Voltage
3V, SD Mode = GND (Low)
200198A2
200198A3
Shutdown Hysteresis Voltage
2.6V, SD Mode = VDD (High)
Shutdown Hysteresis Voltage
2.6V, SD Mode = GND (Low)
200198A4
200198A5
11
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Typical Performance Characteristics (Continued)
Output Power vs.
Output Power vs
Supply Voltage, 4Ω
Supply Voltage, 8Ω
200198B8
200198A6
Output Power vs
Output Power vs
Supply Voltage, 16Ω
Supply Voltage, 32Ω
200198A7
200198A8
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Typical Performance Characteristics (Continued)
Frequency Response vs
Input Capacitor Size
20019854
13
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especially effective when connected to VDD, GND, and the
output pins. Refer to the application information on the
LM4901 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.
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4901 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
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 LM4901. 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.
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.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4901 contains shutdown circuitry that is used to turn off
the amplifier’s bias circuitry. In addition, the LM4901 con-
tains a Shutdown Mode pin, allowing the designer to desig-
nate whether the part will be driven into shutdown with a high
level logic signal or a low level logic signal. This allows the
designer maximum flexibility in device use, as the Shutdown
Mode pin may simply be tied permanently to either VDD or
GND to set the LM4901 as either a "shutdown-high" device
or a "shutdown-low" device, respectively. The device may
then be placed into shutdown mode by toggling the Shut-
down pin to the same state as the Shutdown Mode pin. For
simplicity’s sake, this is called "shutdown same", as the
LM4901 enters shutdown mode whenever the two pins are
in the same logic state. The trigger point for either shutdown
high or shutdown low is shown as a typical value in the
Supply Current vs Shutdown Voltage graphs in the Typical
Performance 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 typical value of 0.1µA. In either case, the shutdown
pin should be tied to a definite voltage to avoid unwanted
state changes.
A bridge configuration, such as the one used in LM4901,
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 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 LM4901 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.
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 (or pull-down, depending on shut-
down high or low application). This scheme guarantees that
the shutdown pin will not float, thus preventing unwanted
state changes.
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
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 LM4901 is tolerant of
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 LM4901. It is
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14
Application Information (Continued)
external component combinations, consideration to compo-
Load Impedance
Input Level
8Ω
1 Vrms
Input Impedance
Bandwidth
20 kΩ
nent values must be used to maximize overall system qual-
ity.
100 Hz–20 kHz 0.25 dB
The LM4901 is unity-gain stable which gives the designer
maximum system flexibility. The LM4901 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.
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.
5V is a standard voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4901 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.
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.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 2.
Selection Of Input Capacitor Size
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 100 Hz to 150 Hz. Thus, using a
large input capacitor may not increase actual system perfor-
mance.
(2)
Rf/Ri = AVD/2
From Equation 2, the minimum AVD is 2.83; use AVD = 3.
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.
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.
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 LM4901 turns
on. The slower the LM4901’s outputs ramp to their quiescent
DC voltage (nominally 1/2 VDD), the smaller the turn-on pop.
Choosing CB equal to 1.0 µF along with a small value of Ci
(in the range of 0.1 µF to 0.39 µF), should produce a virtually
clickless and popless shutdown function. While the device
will function properly, (no oscillations or motorboating), with
CB equal to 0.1 µF, the device will be much more susceptible
to turn-on clicks and pops. Thus, a value of CB equal to
1.0 µF is recommended in all but the most cost sensitive
designs.
fL = 100 Hz/5 = 20 Hz
fH = 20 kHz * 5 = 100 kHz
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 LM4901 GBWP of
2.5MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4901 can still be used without running into bandwidth
limitations.
AUDIO POWER AMPLIFIER DESIGN
A 1W/8Ω Audio Amplifier
Given:
Power Output
1 Wrms
15
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Application Information (Continued)
20019824
FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER
The LM4901 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-
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
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.
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16
Application Information (Continued)
20019829
FIGURE 3. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4901
20019825
FIGURE 4. REFERENCE DESIGN BOARD SCHEMATIC
17
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Application Information (Continued)
LM4901 micro SMD BOARD ARTWORK
Silk Screen
Top Layer
20019878
20019876
Bottom Layer
Inner Layer VDD
20019881
20019880
Inner Layer Ground
20019882
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18
Application Information (Continued)
LM4901 MSOP DEMO BOARD ARTWORK
Silk Screen
Top Layer
20019875
20019879
Bottom Layer
20019877
19
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Application Information (Continued)
LM4901 LLP DEMO BOARD ARTWORK
Composite View
Silk Screen
200198A9
200198B0
Top Layer
Bottom Layer
200198B1
200198B2
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20
Application Information (Continued)
Mono LM4901 Reference Design Boards
Bill of Material
Part Description
Quantity
Reference Designator
LM4901 Audio AMP
1
2
1
2
2
2
U1
Tantalum Capcitor, 1µF
C1, C3
C2
Ceramic Capacitor, 0.39µF
Resistor, 20kΩ, 1/10W
R2, R3
R1, R4
J1, J2
Resistor, 100kΩ, 1/10W
Jumper Header Vertical Mount 2X1 0.100“ spacing
PCB LAYOUT GUIDELINES
Single-Point Power / Ground Connections
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.
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.
GENERAL MIXED SIGNAL LAYOUT
RECOMMENDATION
Placement of Digital and Analog Components
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.
21
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Physical Dimensions inches (millimeters) unless otherwise noted
Note: Unless otherwise specified.
1. Epoxy coating.
2. Recommend non-solder mask defined landing pad.
3. Pin 1 is established by lower left corner with respect to text orientation pins are numbered counterclockwise.
4. 63Sn/37Pb eutectic bump.
5. Reference JEDEC registration MO-211, variation BC.
9-Bump micro SMD
Order Number LM4901IBL, LM4901IBLX
NS Package Number BLA09AAC
X1 = 1.514, X2 = 1.514, X3 = 0.600
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22
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
MSOP
Order Number LM4901MM
NS Package Number MUB10A
23
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LLP
Order Number LM4901LD
NS Package Number LDA10B
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.
National Semiconductor
Corporation
Americas
National Semiconductor
Europe
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
Fax: +49 (0) 180-530 85 86
Email: support@nsc.com
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
Email: ap.support@nsc.com
www.national.com
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.
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