LM4924MMX [TI]
0.04W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10, MSOP-10;
| 型号： | LM4924MMX |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 0.04W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10, MSOP-10 放大器 光电二极管 商用集成电路 |
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LM4924
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SNAS272B –OCTOBER 2004–REVISED APRIL 2013
LM4924 Boomer™ Audio Power Amplifier Series 2 Cell Battery, 40mW Per Channel
Output Capacitor-Less (OCL) Stereo Headphone Audio Amplifier
Check for Samples: LM4924
1
FEATURES
DESCRIPTION
The LM4924 is a Output Capacitor-Less (OCL) stereo
headphone amplifier, which when connected to a
3.0V supply, delivers 40mW per channel to a 16Ω
load with less than 1% THD+N.
23
•
2-Cell 1.5V to 3.6V Battery Operation
OCL Mode for Stereo Headphone Operation
Unity-Gain Stable
•
•
•
“Click and Pop” Suppression Circuitry for
Shutdown On and Off Transients
With the LM4924 packaged in the VSSOP and SON
packages, the customer benefits include low profile
and small size. These packages minimizes PCB area
and maximizes output power.
•
•
Active Low Micropower Shutdown
Thermal Shutdown Protection Circuitry
The LM4924 features circuitry that reduces output
transients (“clicks” and “pops”) during device turn-on
and turn-off, and Mute On and Off. An externally
controlled, low-power consumption, active-low
shutdown mode is also included in the LM4924.
Boomer audio power amplifiers are designed
specifically to use few external components and
provide high quality output power in a surface mount
packages.
APPLICATIONS
•
•
Portable Two-Cell Audio Products
Portable Two-Cell Electronic Devices
KEY SPECIFICATIONS
•
OCL Output Power
–
(RL = 16Ω, VDD = 3.0V, THD+N = 1%),
40mW (Typ)
•
•
Micropower Shutdown Current, 0.1µA (Typ)
Supply Voltage Operating Range,
1.5V < VDD < 3.6V
•
PSRR 100Hz, VDD = 3.0V, AV = 2.5, 66dB (Typ)
Typical Application
Figure 1. Block Diagram
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Boomer is a trademark of Texas Instruments.
2
3
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004–2013, Texas Instruments Incorporated
LM4924
SNAS272B –OCTOBER 2004–REVISED APRIL 2013
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Connection Diagrams
Figure 2. VSSOP Package
Top View
See Package Number DGS for VSSOP
Figure 3. SON Package
Top View
See Package Number DSC0010A
Typical Connections
Rf
50k
Ci
Ri
-
+
0.47 mF 20k
Vin1
Bias
Generator
-
4.7 mF
Cbypass
+
+
Ci
Ri
-
+
0.47 mF 20k
Vin2
Click-Pop
and
Mode Control
Logic
Rf
50k
ShutDown
Controller
Figure 4. Typical OCL Output Configuration Circuit
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings(1)(2)
Supply Voltage
3.8V
−65°C to +150°C
−0.3V to VDD +0.3V
Internally limited
2000V
Storage Temperature
Input Voltage
Power Dissipation(3)
ESD Susceptibility(4)
ESD Susceptibility on pin 7, 8, and 9(4)
ESD Susceptibility(5)
2kV
200V
Junction Temperature
150°C
Small Outline Package Vapor Phase (60sec)
215°C
220°C
Solder Information
Thermal Resistance
Infrared (15 sec)
θJA (typ) DGS
175°C/W
73°C/W
θJA (typ) DSC0010A
(1) 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensue specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments' Sales Office/Distributors for availability and
specifications.
(3) The maximum power dissipation is dictated by TJMAX, θJA, and the ambient temperature TA and must be derated at elevated
temperatures. The maximum allowable power dissipation is PDMAX = (TJMAX − TA)/θJA. For the LM4924, TJMAX = 150°C. For the θJAs,
please see the Application Information section or the Absolute Maximum Ratings section.
(4) Human body model, 100pF discharged through a 1.5kΩ resistor.
(5) Machine model, 220pF–240pF discharged through all pins.
Operating Ratings
T
MIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ +85°C
1.5V ≤ VDD ≤ 3.6V
Temperature Range
Supply Voltage
Electrical Characteristics VDD = 3.0V(1)(2)
The following specifications apply for the circuit shown in Figure 4, unless otherwise specified. AV = 2.5, RL = 16Ω. Limits
apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4924
Units
(Limits)
Typical(3)
Limit(4)
IDD
Quiescent Power Supply Current
Shutdown Current
VIN = 0V, IO = 0A, RL = ∞(5)
1.5
0.1
1
1.9
1
mA (max)
μA (max)
mV (max)
ISD
VSHUTDOWN = GND
VOS
Output Offset Voltage
10
f = 1kHz, per channel
PO
Output Power(6)
OCL (Figure 4), THD+N = 1%
20Hz to 20kHz, A-weighted, Figure 4
PO = 10mW
40
13
0.1
45
30
mW (min)
µVRMS
%
VNO
Output Voltage Noise
THD
0.5
35
Crosstalk
Freq = 1kHz
dB (min)
VRIPPLE = 200mVP-P sine wave
Freq = 100Hz, OCL
PSRR
Power Supply Rejection Ratio
Wake-Up Time
66
58
dB (min)
msec
TWAKE-UP
1.5V ≤ VDD ≤ 3.6V, Figure 4
230
(1) 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensue specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(2) All voltages are measured with respect to the ground (GND) pins unless otherwise specified.
(3) Typicals are measured at 25°C and represent the parametric norm.
(4) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
(5) The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
(6) Output power is measured at the device terminals.
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Electrical Characteristics VDD = 3.0V(1)(2) (continued)
The following specifications apply for the circuit shown in Figure 4, unless otherwise specified. AV = 2.5, RL = 16Ω. Limits
apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4924
Units
(Limits)
Typical(3)
Limit(4)
VIH
Control Logic High
Control Logic Low
1.5V ≤ VDD ≤ 3.6V
0.7VDD
0.3VDD
70
V (min)
V (max)
dB
VIL
1.5V ≤ VDD ≤ 3.6V
Mute
1VPP Reference, RIN = 20k, RFB = 50k
90
Attenuation
Electrical Characteristics VDD = 1.8V(1)(2)
The following specifications apply for the circuit shown in Figure 4, unless otherwise specified. AV = 2.5, RL = 16Ω. Limits
apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4924
Typical(3) Limit(4)
Units
(Limits)
(5)
IDD
Quiescent Power Supply Current
Shutdown Current
VIN = 0V, IO = 0A, RL = ∞
VSHUTDOWN = GND
1.4
0.1
1
mA (max)
μA (max)
mV (max)
ISD
VOS
Output Offset Voltage
f = 1kHz
(6)
PO
Output Power
OCL Per channel, Figure 4, Freq = 1kHz
THD+N = 1%
10
mW
VNO
Output Voltage Noise
20Hz to 20kHz, A-weighted, Figure 4
PO = 5mW
10
0.1
45
µVRMS
%
THD
Crosstalk
Freq = 1kHz
dB (min)
VRIPPLE = 200mVP-P sine wave
Freq = 100Hz, OCL
PSRR
Power Supply Rejection Ratio
66
dB
(1) 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensue specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(2) All voltages are measured with respect to the ground (GND) pins unless otherwise specified.
(3) Typicals are measured at 25°C and represent the parametric norm.
(4) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
(5) The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
(6) Output power is measured at the device terminals.
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Typical Performance Characteristics
THD+N vs Frequency
VDD = 1.8V, PO = 5mW, RL = 16Ω
THD+N vs Frequency
VDD = 1.8V, PO = 5mW, RL = 32Ω
10
1
10
1
0.1
.01
0.1
.01
.001
.0001
.001
.0001
20
200
2k
20k
20
200
2k
20k
20k
100
FREQUENCY (Hz)
Figure 5.
FREQUENCY (Hz)
Figure 6.
THD+N vs Frequency
THD+N vs Frequency
VDD = 3.0V, PO = 10mW, RL = 16Ω
VDD = 3.0V, PO = 10mW, RL = 32Ω
10
1
10
1
0.1
.01
0.1
.01
.001
.0001
.001
.0001
20
200
2k
20k
20
200
2k
FREQUENCY (Hz)
Figure 7.
FREQUENCY (Hz)
Figure 8.
THD+N vs Output Power
VDD = 1.8V, RL = 16Ω, f = 1kHz
THD+N vs Output Power
VDD = 1.8V, RL = 32Ω, f = 1kHz
10
1
10
1
0.1
.01
0.1
.01
10
10
1
100
1
OUTPUT POWER (mW)
OUTPUT POWER (mW)
Figure 9.
Figure 10.
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Typical Performance Characteristics (continued)
THD+N vs Output Power
VDD = 3.0V, RL = 16Ω, f = 1kHz
THD+N vs Output Power
VDD = 3.0V, RL = 32Ω, f = 1kHz
10
1
10
1
0.1
.01
0.1
.01
10
10
1
100
1
100
OUTPUT POWER (mW)
OUTPUT POWER (mW)
Figure 11.
Figure 12.
Power Supply Rejection Ratio
Power Supply Rejection Ratio
VDD = 1.8V, RL = 16Ω,
VDD = 3.0V, RL = 16Ω,
Vripple = 200mVp-p, Input Terminated into 10Ω load
Vripple = 200mVp-p, Input Terminated into 10Ω load
0
0
-20
-20
-40
-60
-40
-60
-80
-80
-100
-100
20
200
2k
20k
20
200
2k
20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 13.
Figure 14.
Noise Floor
VDD = 1.8V, RL = 16Ω
Noise Floor
VDD = 3.0V, RL = 16Ω
100
50
100
50
20
10
5
20
10
5
2
2
4k
12k
20k
4k
12k
20k
8k
16k
8k
16k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 15.
Figure 16.
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Typical Performance Characteristics (continued)
Output Power vs Load Resistance
f = 1kHz. from top to bottom:
VDD = 3.0V, 10%THD+N; VDD = 3.0V, 1%THD+N
VDD = 1.8V, 10%THD+N; VDD = 1.8V, 1%THD+N
60
Channel Separation
RL = 16Ω
40
42
44
50
40
30
46
48
50
20
10
32
48
64
80
96
16
112
20
200
2k
20k
FREQUENCY (Hz)
LOAD RESISTANCE (W)
Figure 17.
Figure 18.
Output Power
vs
Supply Voltage
Output Power vs Supply Voltage
RL = 32Ω, from top to bottom:
THD+N = 10%; THD+N = 1%
RL = 16Ω, from top to bottom:
THD+N = 10%; THD+N = 1%
90
60
50
40
30
70
50
30
10
20
10
3.6
2.2
3.0
2.2
3.6
3.0
1.6
1.6
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Figure 19.
Figure 20.
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Typical Performance Characteristics (continued)
Power Dissipation vs Output Power
VDD = 1.8V, f = 1kHz, from top to bottom:
RL = 16Ω; RL = 32Ω
Power Dissipation vs Output Power
VDD = 3.0V, f = 1kHz, from top to bottom:
RL = 16Ω; RL = 32Ω
120
300
100
80
250
200
150
60
40
20
100
50
0
5
15
20
0
40
60
10
25
20
OUTPUT POWER (mW)
OUTPUT POWER (mW)
Figure 21.
Figure 22.
Supply Current vs Supply Voltage
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.5
2
3
3.5
2.5
4
SUPPLY VOLTAGE (V)
Figure 23.
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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 LM4924 eliminates these output coupling capacitors. VoC is internally configured to apply a 1/2VDD bias
voltage to a stereo headphone jack's sleeve. This voltage matches the quiescent voltage present on the VoA and
VoB 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 headphone speaker terminals. This results in no net DC current flow
through the speaker. AC current flows through a headphone speaker as an audio signal's output amplitude
increases on the speaker's terminal.
The headphone jack's sleeve is not connected to circuit ground. Using the headphone output jack as a line-level
output will place the LM4924's bandgap 1/2VDD bias on a plug's sleeve connection. This presents no difficulty
when the external equipment uses capacitively coupled inputs. For the very small minority of equipment that is
DC-coupled, the LM4924 monitors the current supplied by the amplifier that drives the headphone jack's sleeve.
If this current exceeds 500mAPK, the amplifier is shutdown, protecting the LM4924 and the external equipment.
BYPASS CAPACITOR VALUE SELECTION
Besides minimizing the input capacitor size, careful consideration should be paid to value of CBYPASS, the
capacitor connected to the BYPASS pin. Since CBYPASS determines how fast the LM4924 settles to quiescent
operation, its value is critical when minimizing turn-on pops. The slower the LM4924's outputs ramp to their
quiescent DC voltage (nominally VDD/2), the smaller the turn-on pop. Choosing CB equal to 4.7µF along with a
small value of Ci (in the range of 0.1µF to 0.47µF), produces a click-less and pop-less shutdown function. As
discussed above, choosing Ci no larger than necessary for the desired bandwidth helps minimize clicks and
pops. This ensures that output transients are eliminated when power is first applied or the LM4924 resumes
operation after shutdown.
OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE
The LM4924 contains circuitry that eliminates turn-on and shutdown transients ("clicks and pops"). For this
discussion, turn-on refers to either applying the power supply voltage or when the micro-power shutdown mode
is deactivated.
As the VDD/2 voltage present at the BYPASS pin ramps to its final value, the LM4924's internal amplifiers are
configured as unity gain buffers. An internal current source charges the capacitor connected between the
BYPASS pin and GND in a controlled, linear manner. Ideally, the input and outputs track the voltage applied to
the BYPASS pin. The gain of the internal amplifiers remains unity until the voltage on the bypass pin reaches
VDD/2. As soon as the voltage on the bypass pin is stable, the device becomes fully operational and the amplifier
outputs are reconnected to their respective output pins. Although the BYPASS pin current cannot be modified,
changing the size of CBYPASS alters the device's turn-on time. There is a linear relationship between the size of
CBYPASS and the turn-on time. Here are some typical turn-on times for various values of CBYPASS
.
AMPLIFIER CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4924 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 selecting the ratio of Rf to Ri.
Consequently, the gain for each channel of the IC is
AV = -(Rf/Ri)
(1)
By driving the loads through outputs VO1 and VO2 with VO3 acting as a buffered bias voltage the LM4924 does not
require output coupling capacitors. The typical single-ended amplifier configuration where one side of the load is
connected to ground requires large, expensive output coupling capacitors.
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A configuration such as the one used in the LM4924 has a major advantage over single supply, single-ended
amplifiers. Since the outputs VO1, VO2, and VO3 are all biased at 1/2 VDD, 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 configuration. 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.
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 2
PDMAX = 4(VDD
)
2 / (π2RL)
(2)
It is critical that the maximum junction temperature TJMAX of 150°C is not exceeded. Since the typical application
is for headphone operation (16Ω impedance) using a 3.3V supply the maximum power dissipation is only
138mW. Therefore, power dissipation is not a major concern.
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 3.0V regulator with 10µF tantalum or electrolytic capacitor and a ceramic bypass
capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the
LM4924. A bypass capacitor value in the range of 0.1µF to 1µF is recommended for CS.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the LM4924's shutdown function. Activate micro-power
shutdown by applying a logic-low voltage to the SHUTDOWN pin. When active, the LM4924's micro-power
shutdown feature turns off the amplifier's bias circuitry, reducing the supply 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 voltage that is
higher than ground may increase the shutdown current.
There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw
switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100kΩ pull-up resistor
between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select
normal amplifier operation by opening the switch. Closing the switch connects the SHUTDOWN pin to ground,
activating micro-power shutdown. The switch and resistor ensure that the SHUTDOWN pin will not float. This
prevents unwanted state changes. In a system with a microprocessor or microcontroller, use a digital output to
apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the
pull-up resistor.
SELECTING EXTERNAL COMPONENTS
Selecting proper external components in applications using integrated power amplifiers is critical to optimize
device and system performance. While the LM4924 is tolerant of external component combinations,
consideration to component values must be used to maximize overall system quality.
The LM4924 is unity-gain stable which gives the designer maximum system flexibility. The LM4924 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 complete explanation of proper gain selection
Besides gain, one of the major considerations is the closed-loop bandwidth of the amplifier. The input coupling
capacitor, Ci, forms a first order high pass filter which limits low frequency response. This value should be
chosen based on needed frequency response and turn-on time.
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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 portable 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.
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 quiescent 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.
USING EXTERNAL POWERED SPEAKERS
The LM4924 is designed specifically for headphone operation. Often the headphone output of a device will be
used to drive external powered speakers. The LM4924 has a differential 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.
AUDIO POWER AMPLIFIER DESIGN
A 30mW/32Ω Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
30mWrms
32Ω
1Vrms
20kΩ
Input Impedance
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 Performance Characteristics section, the supply
rail can be easily found.
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 LM4924 to reproduce 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 DISSIPATION section.
Once the power dissipation equations have been addressed, the required differential gain can be determined
from Equation 3.
(3)
From Equation 3, 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.
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 response 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
fL = 100Hz/5 = 20Hz
(4)
and an
fH = 20kHz x 5 = 100kHz
(5)
As mentioned in the SELECTING EXTERNAL COMPONENTS 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 4.
Ci ≥ 1/(2πR ifL)
(6)
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The result is
1/(2π*20kΩ*20Hz) = 0.397µF
(7)
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 LM4924
GBWP of 11MHz. This figure displays that if a designer has a need to design an amplifier with higher differential
gain, the LM4924 can still be used without running into bandwidth limitations.
HIGHER GAIN AUDIO AMPLIFIER
The LM4924 is unity-gain stable and requires no external components besides gain-setting resistors, input
coupling capacitors, and proper supply bypassing in the typical application. However, if a very large closed-loop
differential gain is required, a feedback capacitor (Cf) may be needed to bandwidth limit the amplifier. This
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 frequency roll off is Rf = 20kΩ and Cf = 25pF. These components result in a -3dB point of
approximately 320kHz.
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SNAS272B –OCTOBER 2004–REVISED APRIL 2013
REFERENCE DESIGN BOARD and LAYOUT GUIDELINES
VSSOP & SON BOARDS
A. RPU2 is not required. It is used for test measurement purposes only.
PCB LAYOUT GUIDELINES
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.
Minimization of THD
PCB trace impedance on the power, ground, and all output traces should be minimized to achieve optimal THD
performance. 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 LM4924 in a given application.
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GENERAL MIXED SIGNAL LAYOUT RECOMMENDATION
Power and Ground Circuits
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 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.
Single-Point Power / Ground Connections
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.
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.
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.
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REVISION HISTORY
Changes from Revision A (April 2013) to Revision B
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 14
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PACKAGE OPTION ADDENDUM
www.ti.com
9-Aug-2013
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
LM4924MM/NOPB
ACTIVE
VSSOP
DGS
10
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 85
GB7
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Aug-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LM4924MM/NOPB
VSSOP
DGS
10
1000
178.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Aug-2013
*All dimensions are nominal
Device
Package Type Package Drawing Pins
VSSOP DGS 10
SPQ
Length (mm) Width (mm) Height (mm)
210.0 185.0 35.0
LM4924MM/NOPB
1000
Pack Materials-Page 2
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