LM4910 [NSC]
Output Capacitor-less Stereo 35mW Headphone Amplifier; 输出电容的35MW立体声耳机放大器
| 型号： | LM4910 |
| 厂家： | 
National Semiconductor |
| 描述： | Output Capacitor-less Stereo 35mW Headphone Amplifier |
| 文件： | 总22页 (文件大小：824K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 2003
LM4910
Output Capacitor-less Stereo 35mW Headphone
Amplifier
General Description
Key Specifications
n PSRR at f = 217Hz
65dB (typ)
The LM4910 is an audio power amplifier primarily designed
for headphone applications in portable device applications. It
is capable of delivering 35mW of continuous average power
to a 32Ω load with less than 1% distortion (THD+N) from a
3.3VDC power supply.
n Power Output at VDD = 3.3V, RL = 32Ω, and THD ≤
1%
n Shutdown Current
35mW (typ)
0.1µA (typ)
The LM4910 utilizes a new circuit topology that eliminates
output coupling capacitors and half-supply bypass capaci-
tors (patent pending). The LM4910 contains advanced pop &
click circuitry which eliminates noises caused by transients
that would otherwise occur during turn-on and turn-off.
Features
n Eliminates headphone amplifier output coupling
capacitors (patent pending)
n Eliminates half-supply bypass capacitor (patent pending)
n Advanced pop & click circuitry eliminates noises during
turn-on and turn-off
n Ultra-low current shutdown mode
n Unity-gain stable
n 2.2V - 5.5V operation
n Available in space-saving MSOP, LLP, and SOIC
packages
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. Since the LM4910 does not require
any output coupling capacitors, half-supply bypass capaci-
tors, or bootstrap capacitors, it is ideally suited for low-power
portable applications where minimal space and power con-
sumption are primary requirements.
The LM4910 features a low-power consumption shutdown
mode, activated by driving the shutdown pin with logic low.
Additionally, the LM4910 features an internal thermal shut-
down protection mechanism. The LM4910 is also unity-gain
stable and can be configured by external gain-setting resis-
tors.
Applications
n Mobile Phones
n PDAs
n Portable eletronics devices
n Portable MP3 players
Typical Application
20030565
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation
DS200305
www.national.com
Connection Diagrams
MSOP/SO Package
20030502
Top View
Order Number LM4910MM or LM4910MA
See NS Package Number MUA08A or M08A
MSOP Marking
20030566
Top View
G - Boomer Family
C2 - LM4910MM
SO Marking
20030567
Top View
TT - Die Traceability
Bottom 2 lines - Part Number
LLP Package
20030595
Top View
Order Number LM4910LQ
See NS package Number LQB08A
www.national.com
2
Absolute Maximum Ratings (Note 2)
θJC (MSOP)
θJA (MSOP)
θJC (SOP)
θJA (SOP)
θJC (LQ)
56˚C/W
190˚C/W
35˚C/W
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
150˚C/W
57˚C/W
Supply Voltage (Note 9)
Storage Temperature
6.0V
−65˚C to +150˚C
-0.3V to VDD + 0.3V
Internally Limited
10kV
θJA (LQ)
140˚C/W
Input Voltage
Power Dissipation (Note 3)
ESD Susceptibility Pin 6 (Note 10)
ESD Susceptibility (Note 4)
ESD Susceptibility (Note 5)
Junction Temperature
Operating Ratings
Temperature Range
2000V
TMIN ≤ TA ≤ TMAX
−40˚C ≤ T ≤ 85˚C
A
200V
Supply Voltage (VDD
)
2.2V ≤ VCC ≤ 5.5V
150˚C
Thermal Resistance
Electrical Characteristics VDD = 3.3V (Notes 1, 2)
The following specifications apply for VDD = 3.3V, AV = 1, and 32Ω load unless otherwise specified. Limits apply to TA = 25˚C.
Symbol
Parameter
Conditions
LM4910
Units
(Limits)
Typ
Limit
(Note 6)
(Notes 7,
8)
6
IDD
ISD
VOS
PO
Quiescent Power Supply Current VIN = 0V, 32Ω Load
3.5
0.1
mA (max)
µA (max)
mV (max)
mW (min)
%
Standby Current
Output Offset Voltage
Output Power
VSHUTDOWN = GND
1.0
30
30
5
THD = 1% (max); f = 1kHz
35
THD+N
Total Harmonic Distortion + Noise PO = 30mWrms; f = 1kHz
0.3
65 (f =
217Hz)
65 (f =
1kHz)
VRIPPLE = 200mVp-p sinewave
Power Supply Rejection Ratio
PSRR
dB
Input terminated with 10Ω to ground
VIH
VIL
Shutdown Input Voltage High
Shutdown Input Voltage Low
1.5
0.4
V (min)
V (max)
Electrical Characteristics VDD = 3V (Notes 1, 2)
The following specifications apply for VDD = 3V, AV = 1, and 32Ω load unless otherwise specified. Limits apply to TA = 25˚C.
Symbol
Parameter
Conditions
LM4910
Units
(Limits)
Typ
Limit
(Note 6)
(Notes 7,
8)
6
IDD
ISD
VOS
PO
Quiescent Power Supply Current VIN = 0V, 32Ω Load
3.3
0.1
mA (max)
µA (max)
mV (max)
mW (min)
%
Standby Current
Output Offset Voltage
Output Power
VSHUTDOWN = GND
1.0
30
25
5
THD = 1% (max); f = 1kHz
30
THD+N
Total Harmonic Distortion + Noise PO = 25mWrms; f = 1kHz
0.3
65 (f =
217 Hz)
65 (f =
1kHz)
VRIPPLE = 200mVp-p sinewave
Power Supply Rejection Ratio
PSRR
dB
Input terminated with 10Ω to ground
VIH
VIL
Shutdown Input Voltage High
Shutdown Input Voltage Low
1.5
0.4
V (min)
V (max)
3
www.national.com
Electrical Characteristics VDD = 2.6V (Notes 1, 2)
The following specifications apply for VDD = 2.6V, AV = 1, and 32Ω load unless otherwise specified. Limits apply to TA = 25˚C.
Symbol
Parameter
Conditions
LM4910
Units
(Limits)
Typ
(Note 6)
Limit
(Notes 7,
8)
IDD
ISD
VOS
PO
Quiescent Power Supply Current VIN = 0V, 32Ω Load
3.0
0.1
mA (max)
µA (max)
mV (max)
mW
Standby Current
Output Offset Voltage
Output Power
VSHUTDOWN = GND
5
THD = 1% (max); f = 1kHz
13
THD+N
Total Harmonic Distortion + Noise PO = 10mWrms; f = 1kHz
0.3
%
55 (f =
217Hz)
55 (f =
1kHz)
VRIPPLE = 200mVp-p sinewave
Power Supply Rejection Ratio
PSRR
dB
Input terminated with 10Ω to ground
Note 1: All voltages are measured with respect to the GND 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
currents for more information.
= (T - T )/ θ or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4910, see power derating
JMAX A JA
DMAX
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: 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 part will be protected. If the part is enabled when V is above 6V circuit performance will be
DD
curtailed or the part may be permanently damaged.
Note 10: Human body model, 100pF discharged through a 1.5kΩ resistor, Pin 6 to ground.
External Components Description (Figure 1)
Components
Functional Description
1.
2.
RI
CI
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/(2πRiCi).
Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a
high-pass filter with Ri at fc = 1/(2πRiCi). 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.
www.national.com
4
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Frequency
THD+N vs Frequency
THD+N vs Frequency
20030506
20030507
THD+N vs Frequency
20030508
20030509
THD+N vs Frequency
20030510
20030511
5
www.national.com
Typical Performance Characteristics (Continued)
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
20030516
20030517
20030518
20030520
THD+N vs Output Power
20030515
THD+N vs Output Power
20030519
www.national.com
6
Typical Performance Characteristics (Continued)
Output Power vs
Load Resistance
Output Power vs
Load Resistance
20030523
20030578
Output Power vs
Supply Voltage
Output Power vs
Supply Voltage
20030580
20030579
Output Power vs
Supply Voltage
Power Dissipation vs
Output Power
20030581
20030530
7
www.national.com
Typical Performance Characteristics (Continued)
Power Dissipation vs
Output Power
Power Dissipation vs
Output Power
20030582
20030529
Channel Separation
Power Supply Rejection Ratio
20030583
20030535
Power Supply Rejection Ratio
Power Supply Rejection Ratio
20030584
20030585
www.national.com
8
Typical Performance Characteristics (Continued)
Open Loop Frequency Response
Noise Floor
20030586
20030587
Frequency Response vs
Input Capacitor Size
Supply Current vs
Supply Voltage
20030589
20030588
9
www.national.com
capacitance at the amplifier inputs. A more reliable way to
lower gain or reduce power delivered to the load is to place
a current limiting resistor in series with the load as explained
in the Minimizing Output Noise / Reducing Output Power
section.
Application Information
ELIMINATING OUTPUT COUPLING CAPACITORS
Typical single-supply audio amplifiers that drive single-
ended (SE) headphones use a coupling capacitor on each
SE output. This output coupling capacitor blocks the half-
supply voltage to which the output amplifiers are typically
biased and couples the audio signal to the headphones. The
signal return to circuit ground is through the headphone
jack’s sleeve.
The LM4910 eliminates these output coupling capacitors.
Amp3 is internally configured to apply a bandgap referenced
voltage (VREF = 1.58V) to a stereo headphone jack’s sleeve.
This voltage matches the quiescent voltage present on the
Amp1 and Amp2 outputs that drive the headphones. The
headphones operate in a manner similar to a bridge-tied-
load (BTL). The same DC voltage is applied to both head-
phone speaker terminals. This results in no net DC current
flow through the speaker. AC current flows through a head-
phone speaker as an audio signal’s output amplitude in-
creases on the speaker’s terminal.
20030592
FIGURE 2.
The headphone jack’s sleeve is not connected to circuit
ground. Using the headphone output jack as a line-level
output will place the LM4910’s bandgap referenced voltage
on a plug’s sleeve connection. This presents no difficulty
when the external equipment uses capacitively coupled in-
puts. For the very small minority of equipment that is DC-
coupled, the LM4910 monitors the current supplied by the
amplifier that drives the headphone jack’s sleeve. If this
current exceeds 500mAPK, the amplifier is shutdown, pro-
tecting the LM4910 and the external equipment.
AMPLIFIER CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4910 has three operational
amplifiers internally. Two of the amplifier’s have externally
configurable gain while the other amplifier is internally fixed
at the bias point acting as a unity-gain buffer. The closed-
loop gain of the two configurable amplifiers is set by select-
ing the ratio of Rf to Ri. Consequently, the gain for each
channel of the IC is
AV = -(Rf/Ri)
ELIMINATING THE HALF-SUPPLY BYPASS CAPACITOR
Typical single-supply audio amplifers are normally biased to
1/2VDD in order to maximize the output swing of the audio
signal. This is usually achieved with a simple resistor divider
network from VDD to ground that provides the proper bias
voltage to the amplifier. However, this scheme requires the
use of a half-supply bypass capacitor to improve the bias
voltage’s stability and the amplifier’s PSRR performance.
By driving the loads through outputs VO1 and VO2 with VO3
acting as a buffered bias voltage the LM4910 does not
require output coupling capacitors. The typical single-ended
amplifier configuration where one side of the load is con-
nected to ground requires large, expensive output coupling
capacitors.
A configuration such as the one used in the LM4910 has a
major advantage over single supply, single-ended amplifiers.
Since the outputs VO1, VO2, and VO3 are all biased at VREF
= 1.58V, no net DC voltage exists across each load. This
eliminates the need for output coupling capacitors that are
required in a single-supply, single-ended amplifier configura-
tion. Without output coupling capacitors in a typical single-
supply, single-ended amplifier, the bias voltage is placed
across the load resulting in both increased internal IC power
dissipation and possible loudspeaker damage.
The LM4910 utilizes an internally generated, buffered band-
gap reference voltage as the amplifier’s bias voltage. This
bandgap reference voltage is not a direct function of VDD
and therefore is less susceptible to noise or ripple on the
power supply line. This allows for the LM4910 to have a
stable bias voltage and excellent PSRR performance even
without a half-supply bypass capacitor.
OUTPUT TRANSIENT (’CLICK AND POPS’)
ELIMINATED
The LM4910 contains advanced circuitry that virtually elimi-
nates output transients (’clicks and pops’). This circuitry
prevents all traces of transients when the supply voltage is
first applied or when the part resumes operation after coming
out of shutdown mode. The LM4910 remains in a muted
condition until there is sufficient input signal magnitude
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier. A direct consequence of the increased
power delivered to the load by a bridge amplifier is an
increase in internal power dissipation. The maximum power
dissipation for a given application can be derived from the
power dissipation graphs or from Equation 1.
>
(
5mVRMS, typ) to mask any remaining transient that may
occur. Figure 2 shows the LM4910’s lack of transients in the
differential signal (Trace B) across a 320 load. The LM4910’s
active-low SHUTDOWN pin is driven by the logic signal
shown in Trace A. Trace C is the VO1 output signal and Trace
D is the VO3 output signal.
2
PDMAX = 4(VDD
)
/ (π2RL)
(1)
It is critical that the maximum junction temperature TJMAX of
150˚C is not exceeded. Since the typical application is for
To ensure optimal click and pop performance under low gain
configurations (less than 0dB), it is critical to minimize the
RC combination of the feedback resistor RF and stray input
www.national.com
10
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 and turn-on time.
Application Information (Continued)
headphone operation (32Ω impedance) using a 3.3V supply
the maximum power dissipation is only 138mW. Therefore,
power dissipation is not a major concern.
SELECTION OF INPUT CAPACITOR SIZE
Amplifiying the lowest audio frequencies requires a high
value input coupling capacitor, Ci. A high value capacitor can
be expensive and may compromise space efficiency in por-
table designs. In many cases, however, the headphones
used in portable systems have little ability to reproduce
signals below 60Hz. Applications using headphones with this
limited frequency response reap little improvement by using
a high value input capacitor.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is important
for low noise performance and high power supply rejection.
The capacitor location on the power supply pins should be
as close to the device as possible.
Typical applications employ a 3.3V regulator with 10µF tan-
talum or electrolytic capacitor and a ceramic bypass capaci-
tor which aid in supply stability. This does not eliminate the
need for bypassing the supply nodes of the LM4910. A
bypass capacitor value in the range of 0.1µF to 1µF is
recommended for CS.
In addition to system cost and size, turn-on time is affected
by the size of the input coupling capacitor Ci. A larger input
coupling capacitor requires more charge to reach its quies-
cent DC voltage. This charge comes from the output via the
feedback Thus, by minimizing the capacitor size based on
necessary low frequency response, turn-on time can be
minimized. A small value of Ci (in the range of 0.1µF to
0.39µF), is recommended.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4910’s shutdown function. Activate micro-power shut-
down by applying a logic-low voltage to the SHUTDOWN
pin. When active, the LM4910’s micro-power shutdown fea-
ture turns off the amplifier’s bias circuitry, reducing the sup-
ply current. The trigger point is 0.4V(max) for a logic-low
level, and 1.5V(min) for a logic-high level. The low 0.1µA(typ)
shutdown current is achieved by applying a voltage that is as
near as ground as possible to the SHUTDOWN pin. A volt-
age that is higher than ground may increase the shutdown
current.
USING EXTERNAL POWERED SPEAKERS
The LM4910 is designed specifically for headphone opera-
tion. Often the headphone output of a device will be used to
drive external powered speakers. The LM4910 has a differ-
ential output to eliminate the output coupling capacitors. The
result is a headphone jack sleeve that is connected to VO3
instead of GND. For powered speakers that are designed to
have single-ended signals at the input, the click and pop
circuitry will not be able to eliminate the turn-on/turn-off click
and pop. Unless the inputs to the powered speakers are fully
differential the turn-on/turn-off click and pop will be very
large.
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 100kΩ pull-up resistor between the
SHUTDOWN pin and VDD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by opening the switch. Closing the switch connects the
SHUTDOWN pin to ground, activating micro-power shut-
down. The switch and resistor guarantee that the SHUT-
DOWN pin will not float. This prevents unwanted state
changes. In a system with a microprocessor or microcontrol-
ler, 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.
AUDIO POWER AMPLIFIER DESIGN
A 30mW/32Ω Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
30mWrms
32Ω
1Vrms
Input Impedance
20kΩ
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.
SELECTING EXTERNAL COMPONENTS
Selecting proper external components in applications using
integrated power amplifiers is critical to optimize device and
system performance. While the LM4910 is tolerant of exter-
nal component combinations, consideration to component
values must be used to maximize overall system quality.
Since 3.3V is a standard supply voltage in most applications,
it is chosen for the supply rail in this example. Extra supply
voltage creates headroom that allows the LM4910 to repro-
duce peaks in excess of 30mW without producing audible
distortion. At this time, the designer must make sure that the
power supply choice along with the output impedance does
no violate the conditions explained in the Power Dissipa-
tion section.
The LM4910 is unity-gain stable which gives the designer
maximum system flexibility. The LM4910 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 1Vrms are available
from sources such as audio codecs. Very large values
should not be used for the gain-setting resistors. Values for
Ri and Rf should be less than 1MΩ. Please refer to the
section, Audio Power Amplifier Design, for a more com-
plete explanation of proper gain selection
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
(2)
11
www.national.com
Application Information (Continued)
As mentioned in the Selecting Proper External Compo-
nents section, Ri and Ci create a highpass filter that sets the
amplifier’s lower bandpass frequency limit. Find the coupling
capacitor’s value using Equation (3).
From Equation 2, the minimum AV is 0.98; use AV = 1. Since
the desired input impedance is 20kΩ, and with AV equal to 1,
a ratio of 1:1 results from Equation 1 for Rf to Ri. The values
are chosen with Ri = 20kΩ and Rf = 20kΩ.
Ci≥ 1/(2πR ifL)
(5)
The last step in this design example is setting the amplifier’s
−3dB frequency bandwidth. To achieve the desired 0.25dB
pass band magnitude variation limit, the low frequency re-
sponse must extend to at least one-fifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the 0.25dB
desired limit. The results are an
The result is
*
*
1/(2π 20kΩ 20Hz) = 0.397µF
Use a 0.39µF capacitor, the closest standard value.
The high frequency pole is determined by the product of the
desired frequency pole, fH, and the differential gain, AV. With
an AV = 1 and fH = 100kHz, the resulting GBWP = 100kHz
which is much smaller than the LM4910 GBWP of 11MHz.
This figure displays that if a designer has a need to design
an amplifier with higher differential gain, the LM4910 can still
be used without running into bandwidth limitations.
fL = 100Hz/5 = 20Hz
(3)
and an
fH = 20kHz x 5 = 100kHz
(4)
MINIMIZING OUTPUT NOISE / REDUCING OUTPUT POWER
20030568
FIGURE 3.
Output noise delivered to the load can be minimized with the
use of an external resistor, RSERIES, placed in series with
each load as shown in Figure 3. RSERIES forms a voltage
divider with the impedance of the headphone driver RL. As a
Figure 4 shows an optional resistor connected between the
amplifier output that drives the headphone jack sleeve and
ground. This resistor provides a ground path that supressed
power supply hum. This hum may occur in applications such
as notebook computers in a shutdown condition and con-
nected to an external powered speaker. The resistor’s 100Ω
value is a suggested starting point. Its final value must be
determined based on the tradeoff between the amount of
noise suppression that may be needed and minimizing the
additional current drawn by the resistor (25mA for a 100Ω
resistor and a 5V supply).
result, output noise is attenuated by the factor RL / (RL
+
RSERIES). Figure 4 illustrates the relationship between output
noise and RSERIES for different loads. RSERIES also de-
creases output power delivered to the load by the factor RL
/ (RL + RSERIES)2. However, this may not pose a problem
since most headphone applications require less than 10mW
@
of output power. Figure 5 illustrates output power ( 1%
THD+N) vs RSERIES for different loads.
www.national.com
12
Application Information (Continued)
ESD PROTECTION
As stated in the Absolute Maximum Ratings, pin 6 (Vo3) on
the LM4910 has a maximum ESD susceptibility rating of
10kV. For higher ESD voltages, the addition of a PCDN042
dual transil (from California Micro Devices), as shown in
Figure 4, will provide additional protection.
20030594
FIGURE 4. The PCDN042 provides additional ESD protection beyond the 10kV shown in the Absolute Maximum
Ratings for the Vo3 output
Output Noise vs RSERIES
20030590
FIGURE 5.
13
www.national.com
Application Information (Continued)
Output Power vs RSERIES
20030591
FIGURE 6.
HIGHER GAIN AUDIO AMPLIFIER
20030593
FIGURE 7.
www.national.com
14
feedback capacitor creates a low pass filter that eliminates
possible high frequency oscillations. Care should be taken
when calculating the -3dB frequency in that an incorrect
combination of Rf and Cf will cause frequency response roll
off before 20kHz. A typical combination of feedback resistor
and capacitor that will not produce audio band high fre-
quency roll off is Rf = 20kΩ and Cf = 25pF. These compo-
nents result in a -3dB point of approximately 320kHz.
Application Information (Continued)
The LM4910 is unity-gain stable and requires no external
components besides gain-setting resistors, input coupling
capacitors, and proper supply bypassing in the typical appli-
cation. However, if a very large closed-loop differential gain
is required, a feedback capacitor (Cf) may be needed as
shown in Figure 6 to bandwidth limit the amplifier. This
REFERENCE DESIGN BOARD and LAYOUT GUIDELINES
MSOP & SO BOARDS
20030569
FIGURE 8.
(Note: RPU2 is not required. It is used for test measurement purposes only.)
15
www.national.com
Application Information (Continued)
LM4910 SO DEMO BOARD ARTWORK
Composite View
Silk Screen
20030571
20030570
Top Layer
Bottom Layer
20030573
20030572
www.national.com
16
Application Information (Continued)
LM4910 MSOP DEMO BOARD ARTWORK
Composite View
Silk Screen
20030575
20030574
Top Layer
Bottom Layer
20030577
20030576
17
www.national.com
Application Information (Continued)
LM4910 LLP DEMO BOARD ARTWORK
Composite View
Silk Screen
20030598
20030597
Top Layer
Bottom Layer
20030599
20030596
www.national.com
18
Application Information (Continued)
LM4910 Reference Design Boards
Bill of Materials
Part Description
LM4910 Mono Reference Design Board
LM4910 Audio AMP
Qty
1
Ref Designator
1
U1
Cs
Tantalum Cap 1µF 16V 10
1
Ceramic Cap 0.39µF 50V Z50 20
Resistor 20kΩ 1/10W 5
2
Ci
4
Ri, Rf
Rpu
J1
Resistor 100kΩ 1/10W 5
1
Jumper Header Vertical Mount 2X1, 0.100
1
PCB LAYOUT GUIDELINES
greatly enhance 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 may
be some jumpers.
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.
Single-Point Power / Ground Connections
Minimization of THD
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. Further, place digital and analog
power traces over the corresponding digital and analog
ground traces to minimize noise coupling.
PCB trace impedance on the power, ground, and all output
traces should be minimized to achieve optimal THD perfor-
mance. Therefore, use PCB traces that are as wide as
possible for these connections. As the gain of the amplifier is
increased, the trace impedance will have an ever increasing
adverse affect on THD performance. At unity-gain (0dB) the
parasitic trace impedance effect on THD performance is
reduced but still a negative factor in the THD performance of
the LM4910 in a given application.
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.
GENERAL MIXED SIGNAL LAYOUT
RECOMMENDATION
Avoiding Typical Design / Layout Problems
Power and Ground Circuits
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.
For two 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
(bringing individual traces back to a central point rather than
daisy chaining traces together in a serial manner) can
19
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted
MSOP
Order Number LM4910MM
NS Package Number MUA08A
www.national.com
20
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
SO
Order Number LM4910MA
NS Package Number M08A
LQ
Order Number LM4910LQ
NS Package Number LQB08A
21
www.national.com
Notes
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
Americas Customer
Support Center
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
National Semiconductor
Asia Pacific Customer
Support Center
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
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
Fax: 65-6250 4466
Email: ap.support@nsc.com
Tel: 65-6254 4466
Email: nsj.crc@jksmtp.nsc.com
Tel: 81-3-5639-7560
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.
相关型号：
SI9130DB
5- and 3.3-V Step-Down Synchronous ConvertersWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135LG-T1
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135LG-T1-E3
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135_11
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9136_11
Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130CG-T1-E3
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130LG-T1-E3
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130_11
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137DB
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137LG
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9122E
500-kHz Half-Bridge DC/DC Controller with Integrated Secondary Synchronous Rectification DriversWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
©2020 ICPDF网 联系我们和版权申明