LM4674 [NSC]
Filterless 2.5W Stereo Class D Audio Power Amplifier; 无滤波2.5W立体声D类音频功率放大器
| 型号： | LM4674 |
| 厂家： | 
National Semiconductor |
| 描述： | Filterless 2.5W Stereo Class D Audio Power Amplifier |
| 文件： | 总18页 (文件大小：842K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
December 2005
LM4674
Filterless 2.5W Stereo Class D Audio Power Amplifier
General Description
Key Specifications
The LM4674 is a single supply, high efficiency, 2.5W/
channel, filterless switching audio amplifier. A low noise
PWM architecture eliminates the output filter, reducing ex-
ternal component count, board area consumption, system
cost, and simplifying design.
j
Efficiency at 3.6V, 100mW into 8Ω
80% (typ)
85% (typ)
85% (typ)
j
Efficiency at 3.6V, 500mW into 8Ω
j
Efficiency at 5V, 1W into 8Ω
j
j
j
j
Quiescent Power Supply Current
at 3.6V supply
The LM4674 is designed to meet the demands of mobile
phones and other portable communication devices. Operat-
ing from a single 5V supply, the device is capable of deliv-
ering 2.5W/channel of continuous output power to a 4Ω load
with less than 10% THD+N. Flexible power supply require-
ments allow operation from 2.4V to 5.5V.
4mA
Power Output at VDD = 5V,
RL = 4Ω, THD ≤ 10%
Power Output at VDD = 5V,
RL = 8Ω, THD ≤ 10%
Shutdown current
2.5W (typ)
1.5W (typ)
0.1µA (typ)
The LM4674 features high efficiency compared to conven-
tional Class AB amplifiers. When driving and 8Ω speaker
from a 3.6V supply, the device features 85% efficiency at PO
= 500mW. Four gain options are pin selectable through the
GAIN0 and GAIN1 pins.
Features
n Output Short Circuit Protection
n Stereo Class D operation
n No output filter required
n Logic selectable gain
Output short circuit protection prevents the device from be-
ing damaged during fault conditions. Superior click and pop
suppression eliminates audible transients on power-up/down
and during shutdown. Independent left/right shutdown con-
trols maximizes power savings in mixed mono/stereo appli-
cations.
n Independent shutdown control
n Minimum external components
n Click and Pop suppression
n Micro-power shutdown
n Available in space-saving 2mm x 2mm x 0.6mm micro
SMD package
Applications
n Mobile phones
n PDAs
n Laptops
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation
DS201674
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Typical Application
20167402
* Bypass output should be left floating for proper operation in most applications. See Application Information for details.
FIGURE 1. Typical Audio Amplifier Application Circuit
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2
Connection Diagrams
TL Package (2mmx2mmx0.6mm)
20167401
Top View
Order Number LM4674TL
See NS Package Number TL1611A
LM4674TL Markings
20167425
Top View
XY = 2 digit datecode
TT = Die traceability
G = Boomer Family
G2 = LM4674TL
3
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Absolute Maximum Ratings (Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Junction Temperature (TJMAX
Thermal Resistance
θJA
)
150˚C
45.7˚C/W
Supply Voltage (Note 1)
Storage Temperature
Input Voltage
6.0V
−65˚C to +150˚C
–0.3V to VDD +0.3V
Internally Limited
Operating Ratings (Note 1) (Note 2)
Temperature Range
TMIN ≤ TA ≤ TMAX
−40˚C ≤ TA ≤ 85˚C
2.4V ≤ VDD ≤ 5.5V
Power Dissipation (Note 3)
Supply Voltage
ESD Susceptibility, all other pins (Note 4)
ESD Susceptibility (Note 5)
2000V
200V
Electrical Characteristics VDD = 3.6V (Notes 1, 2)
The following specifications apply for AV = 6dB, RL = 15µH + 8Ω + 15µH, f = 1kHz unless otherwise specified. Limits apply
for TA = 25˚C.
LM4674
Units
Symbol
VOS
Parameter
Conditions
Typical
(Note 6)
5
Limit
(Limits)
(Note 7)
Differential Output Offset Voltage
VIN = 0, VDD = 2.4V to 5.0V
mV
∞
,
VIN = 0, RL
=
4
6
Both channels active, VDD = 3.6V
IDD
Quiescent Power Supply Current
mA
∞
,
VIN = 0, RL
=
5
7.5
Both channels active, VDD = 5V
VSD1 = VSD2 = GND
ISD
Shutdown Current
0.03
1
µA
VSDIH
VSDIL
TWU
Shutdown Voltage Input High
Shutdown Voltage Input Low
Wake Up Time
1.4
0.4
V (min)
V (max)
ms
VSHUTDOWN = 0.4V
GAIN0, GAIN1 = GND
GAIN0 = VDD, GAIN1 = GND
GAIN0 = GND, GAIN1 = VDD
GAIN0, GAIN1 = VDD
AV = 6dB
0.5
6
6
0.5
12
12 0.5
18 0.5
24 0.5
AV
Gain
dB
18
24
28
AV = 12dB
18.75
11.25
6.25
RIN
Input Resistance
kΩ
AV = 18dB
AV = 24dB
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Electrical Characteristics VDD = 3.6V (Notes 1, 2)
The following specifications apply for AV = 6dB, RL = 15µH + 8Ω + 15µH, f = 1kHz unless otherwise specified. Limits apply for
TA = 25˚C. (Continued)
LM4674
Units
Symbol
Parameter
Conditions
Typical
Limit
(Limits)
(Note 6)
(Note 7)
RL = 15µH + 4Ω + 15µH, THD = 10%
f = 1kHz, 22kHz BW
VDD = 5V
2.5
1.2
VDD = 3.6V
W
VDD = 2.5V
0.530
RL = 15µH + 8Ω + 15µH, THD = 10%
f = 1kHz, 22kHz BW
VDD = 5V
1.5
0.78
0.350
VDD = 3.6V
0.6
W
W
VDD = 2.5V
PO
Output Power
RL = 15µH + 4Ω + 15µH, THD = 1%
f = 1kHz, 22kHz BW
VDD = 5V
1.9
1
VDD = 3.6V
VDD = 2.5V
0.430
RL = 15µH + 8Ω + 15µH, THD = 1%
f = 1kHz, 22kHz BW
VDD = 5V
1.25
0.63
0.285
0.07
0.05
VDD = 3.6V
W
%
VDD = 2.5V
PO = 500mW, f = 1kHz, RL = 8Ω
PO = 300mW, f = 1kHz, RL = 8Ω
VRIPPLE = 200mVP-P Sine,
fRipple = 217Hz, Inputs AC GND, CI
= 1µF, input referred
VRIPPLE = 1VP-P Sine,
fRipple = 1kHz, Inputs AC GND, CI =
1µF, input referred
THD+N
PSRR
Total Harmonic Distortion
75
75
Power Supply Rejection Ratio
dB
VRIPPLE = 1VP-P
CMRR
Common Mode Rejection Ratio
Efficiency
67
85
dB
%
fRIPPLE = 217Hz
PO = 1W, f = 1kHz,
RL = 8Ω, VDD = 5V
PO = 500mW, f = 1kHz
VDD = 5V, PO = 1W
Input referred, A-Weighted Filter
η
Crosstalk
84
96
20
dB
dB
µV
SNR
Signal to Noise Ratio
Output Noise
eOS
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
currents for more information.
= (T
– T )/ θ or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4674 see power derating
DMAX
JMAX A JA
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).
5
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External Components Description
(Figure 1)
Components
Functional Description
1.
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.
Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals.
2.
CI
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Block Diagrams
20167437
7
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Block Diagrams (Continued)
20167438
Differential Input Configuration
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Typical Performance Characteristics
THD+N vs Output Power
THD+N vs Output Power
f = 1kHz, AV = 24dB, RL = 8Ω
f = 1kHz, AV = 6dB, RL = 8Ω
20167439
20167440
THD+N vs Output Power
THD+N vs Output Power
f= 1kHz, AV = 24dB, RL = 4Ω
f = 1kHz, AV = 6dB, RL = 4Ω
20167441
20167442
THD+N vs Frequency
THD+N vs Frequency
VDD = 2.5V, POUT = 100mW, RL = 8Ω
VDD = 3.6V, POUT = 250mW, RL = 8Ω
20167443
20167444
9
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Typical Performance Characteristics (Continued)
THD+N vs Frequency
THD+N vs Frequency
VDD = 5V, POUT = 375mW, RL = 8Ω
VDD = 2. 5V, POUT = 100mW, RL = 4Ω
20167445
20167446
THD+N vs Frequency
THD+N vs Frequency
VDD = 3.6V, POUT = 250mW, RL = 4Ω
VDD = 5V, POUT = 375mW, RL = 4Ω
20167447
20167448
Efficiency vs. Output Power
Efficiency vs. Output Power
RL = 4Ω, f = 1kHz
RL = 8Ω, f = 1kHz
20167449
20167450
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Typical Performance Characteristics (Continued)
Power Dissipation vs. Output Power
Power Dissipation vs. Output Power
RL = 4Ω, f = 1kHz
RL = 8Ω, f = 1kHz
20167451
20167452
Output Power vs. Supply Voltage
Output Power vs. Supply Voltage
RL = 4Ω, f = 1kHz
RL = 8Ω, f = 1kHz
20167453
20167454
PSRR vs. Frequency
Crosstalk vs. Frequency
VDD = 3.6V, VRIPPLE= 200mVP-P, RL = 8Ω
VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω
20167422
20167455
11
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Typical Performance Characteristics (Continued)
CMRR vs. Frequency
VDD = 3.6V, VCM = 1VP-P, RL = 8Ω
Supply Current vs. Supply Voltage
No Load
20167457
20167458
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Application Information
GENERAL AMPLIFIER FUNCTION
unwanted state changes when /SD_ is floating. To minimize
shutdown current, /SD_ should be driven to GND or left
floating. If /SD_ is not driven to GND or floating, an increase
in shutdown supply current will be noticed.
The LM4674 stereo Class D audio power amplifier features a
filterless modulation scheme that reduces external compo-
nent count, conserving board space and reducing system
cost. The outputs of the device transition from VDD to GND
with a 300kHz switching frequency. With no signal applied,
the outputs (OUT_A and OUT_B) switch with a 50% duty
cycle, in phase, causing the two outputs to cancel. This
cancellation results in no net voltage across the speaker,
thus there is no current to the load in the idle state.
SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION
The LM4674 is compatible with single-ended sources. When
configured for single-ended inputs, input capacitors must be
used to block and DC component at the input of the device.
Figure 3 shows the typical single-ended applications circuit.
With the input signal applied, the duty cycle (pulse width) of
the LM4674 outputs changes. For increasing output voltage,
the duty cycle of OUT_A increases, while the duty cycle of
OUT_B decreases. For decreasing output voltages, the con-
verse occurs. The difference between the two pulse widths
yields the differential output voltage.
AUDIO AMPLIFIER POWER SUPPLY
BYPASSING/FILTERING
Proper power supply bypassing is critical for low noise per-
formance and high PSRR. Place the supply bypass capaci-
tor as close to the device as possible. Typical applications
employ a voltage regulator with 10µF and 0.1µF bypass
capacitors that increase supply stability. These capacitors do
not eliminate the need for bypassing of the LM4674 supply
pins. A 1µF capacitor is recommended.
DIFFERENTIAL AMPLIFIER EXPLANATION
As logic supplies continue to shrink, system designers are
increasingly turning to differential analog signal handling to
preserve signal to noise ratios with restricted voltage signs.
The LM4674 features two fully differential amplifiers. A dif-
ferential amplifier amplifies the difference between the two
input signals. Traditional audio power amplifiers have typi-
cally offered only single-ended inputs resulting in a 6dB
reduction of SNR relative to differential inputs. The LM4674
also offers the possibility of DC input coupling which elimi-
nates the input coupling capacitors. A major benefit of the
fully differential amplifier is the improved common mode
rejection ratio (CMRR) over single ended input amplifiers.
The increased CMRR of the differential amplifier reduces
sensitivity to ground offset related noise injection, especially
important in noisy systems.
AUDIO AMPLIFIER INPUT CAPACITOR SELECTION
Input capacitors may be required for some applications, or
when the audio source is single-ended. Input capacitors
block the DC component of the audio signal, eliminating any
conflict between the DC component of the audio source and
the bias voltage of the LM4674. The input capacitors create
a high-pass filter with the input resistors RI. The -3dB point of
the high pass filter is found using Equation 1 below.
f = 1 / 2πRINCIN
The values for RI can be found in the EC table for each gain
setting.
(1)
The input capacitors can also be used to remove low fre-
quency content from the audio signal. Small speakers can-
not reproduce, and may even be damaged by low frequen-
cies. High pass filtering the audio signal helps protect the
speakers. When the LM4674 is using a single-ended source,
power supply noise on the ground is seen as an input signal.
Setting the high-pass filter point above the power supply
noise frequencies, 217Hz in a GSM phone, for example,
filters out the noise such that it is not amplified and heard on
the output. Capacitors with a tolerance of 10% or better are
recommended for impedance matching and improved
CMRR and PSRR.
POWER DISSIPATION AND EFFICIENCY
The major benefit of a Class D amplifier is increased effi-
ciency versus a Class AB. The efficiency of the LM4674 is
attributed to the region of operation of the transistors in the
output stage. The Class D output stage acts as current
steering switches, consuming negligible amounts of power
compared to their Class AB counterparts. Most of the power
loss associated with the output stage is due to the IR loss of
the MOSFET on-resistance, along with switching losses due
to gate charge.
SHUTDOWN FUNCTION
AUDIO AMPLIFIER GAIN SETTING
The LM4674 features independent left and right channel
shutdown controls, allowing each channel to be disabled
independently. /SDR controls the right channel, while /SDL
controls the left channel. Driving either low disables the
corresponding channel, reducing supply current to 0.03µA.
The LM4674 features four internally configured gain settings.
The device gain is selected through the two logic inputs, G0
and G1. The gain settings are as shown in the following
table.
G1
G0
GAIN
It is best to switch between ground and VDD for minimum
current consumption while in shutdown. The LM4674 may be
V/V
2
dB
6
disabled with shutdown voltages in between GND and VDD
,
0
0
1
1
0
1
0
1
the idle current will be greater than the typical 0.03µA value.
Increased THD+N may also be observed when a voltage of
less than VDD is applied to /SD_ for logic levels between
GND and VDD Bypass /SD_ with a 0.1µF capacitor.
4
12
18
24
8
16
The LM4674 shutdown inputs have internal pulldown resis-
tors. The purpose of these resistors is to eliminate any
13
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The inductive nature of the transducer load can also result in
overshoot on one of both edges, clamped by the parasitic
diodes to GND and VDD in each case. From an EMI stand-
point, this is an aggressive waveform that can radiate or
conduct to other components in the system and cause inter-
ference. In is essential to keep the power and output traces
short and well shielded if possible. Use of ground planes
beads and micros-strip layout techniques are all useful in
preventing unwanted interference.
Application Information (Continued)
PCB LAYOUT GUIDELINES
As output power increases, interconnect resistance (PCB
traces and wires) between the amplifier, load and power
supply create a voltage drop. The voltage loss due to the
traces between the LM4674 and the load results in lower
output power and decreased efficiency. Higher trace resis-
tance between the supply and the LM4674 has the same
effect as a poorly regulated supply, increasing ripple on the
supply line, and reducing peak output power. The effects of
residual trace resistance increases as output current in-
creases due to higher output power, decreased load imped-
ance or both. To maintain the highest output voltage swing
and corresponding peak output power, the PCB traces that
connect the output pins to the load and the supply pins to the
power supply should be as wide as possible to minimize
trace resistance.
As the distance from the LM4674 and the speaker increases,
the amount of EMI radiation increases due to the output
wires or traces acting as antennas become more efficient
with length. Ferrite chip inductors places close to the
LM4674 outputs may be needed to reduce EMI radiation.
The use of power and ground planes will give the best
THD+N performance. In addition to reducing trace resis-
tance, the use of power planes creates parasitic capacitors
that help to filter the power supply line.
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Application Information (Continued)
20167426
Differential Input Configuration
FIGURE 2.
15
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Application Information (Continued)
20167438
Single-Ended Input Configuration
FIGURE 3.
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Revision Table
Rev
1.0
Date
Description
1st PDF edited after copied LM4671.
Added graphics 22, 23, and 24. Also did
some texts edits.
10/4/05
12/15/05
1.1
1.2
12/16/05
Edited 201674 23, then released D/S to
the WEB.
17
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Physical Dimensions inches (millimeters) unless otherwise noted
16 Bump micro SMD
Order Number LM4674TL
NS Package Number TLA1611A
X1 = 2mm X2 = 2mm X3 = 0.6mm
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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CORPORATION. As used herein:
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(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.
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