NSC LM4674TL

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 external component count, board area consumption, system
cost, and simplifying design.
The LM4674 is designed to meet the demands of mobile
phones and other portable communication devices. Operating from a single 5V supply, the device is capable of delivering 2.5W/channel of continuous output power to a 4Ω load
with less than 10% THD+N. Flexible power supply requirements allow operation from 2.4V to 5.5V.
j Efficiency at 3.6V, 100mW into 8Ω
80% (typ)
j Efficiency at 3.6V, 500mW into 8Ω
85% (typ)
j Efficiency at 5V, 1W into 8Ω
85% (typ)
The LM4674 features high efficiency compared to conventional 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.
j Shutdown current
Output short circuit protection prevents the device from being damaged during fault conditions. Superior click and pop
suppression eliminates audible transients on power-up/down
and during shutdown. Independent left/right shutdown controls maximizes power savings in mixed mono/stereo applications.
j Quiescent Power Supply Current
at 3.6V supply
j Power Output at VDD = 5V,
RL = 4Ω, THD ≤ 10%
j Power Output at VDD = 5V,
RL = 8Ω, THD ≤ 10%
4mA
2.5W (typ)
1.5W (typ)
0.1µA (typ)
Features
n
n
n
n
n
n
n
n
n
Output Short Circuit Protection
Stereo Class D operation
No output filter required
Logic selectable gain
Independent shutdown control
Minimum external components
Click and Pop suppression
Micro-power shutdown
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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LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier
December 2005
LM4674
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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LM4674
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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LM4674
Absolute Maximum Ratings (Notes 1, 2)
Junction Temperature (TJMAX)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Thermal Resistance
Supply Voltage (Note 1)
Operating Ratings (Note 1) (Note 2)
θJA
6.0V
Storage Temperature
−65˚C to +150˚C
Power Dissipation (Note 3)
ESD Susceptibility, all other pins (Note 4)
ESD Susceptibility (Note 5)
45.7˚C/W
Temperature Range
–0.3V to VDD +0.3V
Input Voltage
150˚C
TMIN ≤ TA ≤ TMAX
Internally Limited
−40˚C ≤ TA ≤ 85˚C
2.4V ≤ VDD ≤ 5.5V
Supply Voltage
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
Symbol
VOS
IDD
Parameter
Differential Output Offset Voltage
Quiescent Power Supply Current
ISD
Shutdown Current
VSDIH
Shutdown Voltage Input High
VSDIL
Shutdown Voltage Input Low
TWU
Wake Up Time
AV
RIN
Gain
Input Resistance
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Conditions
Typical
Limit
(Note 6)
(Note 7)
VIN = 0, VDD = 2.4V to 5.0V
5
VIN = 0, RL = ∞,
Both channels active, VDD = 3.6V
4
6
VIN = 0, RL = ∞,
Both channels active, VDD = 5V
5
7.5
VSD1 = VSD2 = GND
VSHUTDOWN = 0.4V
mV
mA
0.03
1
µA
1.4
V (min)
0.4
V (max)
0.5
ms
GAIN0, GAIN1 = GND
6
6 ± 0.5
GAIN0 = VDD, GAIN1 = GND
12
12 ± 0.5
GAIN0 = GND, GAIN1 = VDD
18
18 ± 0.5
GAIN0, GAIN1 = VDD
24
24 ± 0.5
AV = 6dB
28
AV = 12dB
18.75
AV = 18dB
11.25
AV = 24dB
6.25
4
Units
(Limits)
dB
kΩ
LM4674
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Note 7)
Units
(Limits)
RL = 15µH + 4Ω + 15µH, THD = 10%
f = 1kHz, 22kHz BW
VDD = 5V
2.5
VDD = 3.6V
1.2
VDD = 2.5V
0.530
W
RL = 15µH + 8Ω + 15µH, THD = 10%
f = 1kHz, 22kHz BW
VDD = 5V
PO
Output Power
1.5
VDD = 3.6V
0.78
VDD = 2.5V
0.350
0.6
W
RL = 15µH + 4Ω + 15µH, THD = 1%
f = 1kHz, 22kHz BW
VDD = 5V
1.9
VDD = 3.6V
1
VDD = 2.5V
0.430
W
RL = 15µH + 8Ω + 15µH, THD = 1%
f = 1kHz, 22kHz BW
VDD = 5V
THD+N
PSRR
Total Harmonic Distortion
Power Supply Rejection Ratio
1.25
VDD = 3.6V
0.63
VDD = 2.5V
0.285
PO = 500mW, f = 1kHz, RL = 8Ω
0.07
PO = 300mW, f = 1kHz, RL = 8Ω
0.05
VRIPPLE = 200mVP-P Sine,
fRipple = 217Hz, Inputs AC GND, CI
= 1µF, input referred
75
VRIPPLE = 1VP-P Sine,
fRipple = 1kHz, Inputs AC GND, CI =
1µF, input referred
75
W
%
dB
CMRR
Common Mode Rejection Ratio
VRIPPLE = 1VP-P
fRIPPLE = 217Hz
67
dB
η
Efficiency
PO = 1W, f = 1kHz,
RL = 8Ω, VDD = 5V
85
%
Crosstalk
PO = 500mW, f = 1kHz
84
dB
SNR
Signal to Noise Ratio
VDD = 5V, PO = 1W
96
dB
eOS
Output Noise
Input referred, A-Weighted Filter
20
µV
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 TJMAX, θJA, and the ambient temperature, TA. The maximum
allowable power dissipation is PDMAX = (TJMAX – TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4674 see power derating
currents for more information.
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 5: Machine Model, 220pF–240pF discharged through all pins.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
5
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LM4674
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
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.
2.
CI
Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals.
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LM4674
Block Diagrams
20167437
7
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LM4674
Block Diagrams
(Continued)
20167438
Differential Input Configuration
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LM4674
Typical Performance Characteristics
THD+N vs Output Power
f = 1kHz, AV = 6dB, RL = 8Ω
THD+N vs Output Power
f = 1kHz, AV = 24dB, RL = 8Ω
20167439
20167440
THD+N vs Output Power
f = 1kHz, AV = 6dB, RL = 4Ω
THD+N vs Output Power
f= 1kHz, AV = 24dB, RL = 4Ω
20167441
20167442
THD+N vs Frequency
VDD = 3.6V, POUT = 250mW, RL = 8Ω
THD+N vs Frequency
VDD = 2.5V, POUT = 100mW, RL = 8Ω
20167443
20167444
9
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LM4674
Typical Performance Characteristics
(Continued)
THD+N vs Frequency
VDD = 5V, POUT = 375mW, RL = 8Ω
THD+N vs Frequency
VDD = 2. 5V, POUT = 100mW, RL = 4Ω
20167445
20167446
THD+N vs Frequency
VDD = 5V, POUT = 375mW, RL = 4Ω
THD+N vs Frequency
VDD = 3.6V, POUT = 250mW, RL = 4Ω
20167447
20167448
Efficiency vs. Output Power
RL = 8Ω, f = 1kHz
Efficiency vs. Output Power
RL = 4Ω, f = 1kHz
20167449
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20167450
10
(Continued)
Power Dissipation vs. Output Power
RL = 4Ω, f = 1kHz
Power Dissipation vs. Output Power
RL = 8Ω, f = 1kHz
20167451
20167452
Output Power vs. Supply Voltage
RL = 8Ω, f = 1kHz
Output Power vs. Supply Voltage
RL = 4Ω, f = 1kHz
20167453
20167454
Crosstalk vs. Frequency
VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω
PSRR vs. Frequency
VDD = 3.6V, VRIPPLE= 200mVP-P, RL = 8Ω
20167422
20167455
11
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LM4674
Typical Performance Characteristics
LM4674
Typical Performance Characteristics
(Continued)
CMRR vs. Frequency
VDD = 3.6V, VCM = 1VP-P, RL = 8Ω
Supply Current vs. Supply Voltage
No Load
20167457
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20167458
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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.
GENERAL AMPLIFIER FUNCTION
The LM4674 stereo Class D audio power amplifier features a
filterless modulation scheme that reduces external component 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 converse 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 performance and high PSRR. Place the supply bypass capacitor 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 differential amplifier amplifies the difference between the two
input signals. Traditional audio power amplifiers have typically 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 eliminates 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.
(1)
f = 1 / 2πRINCIN
The values for RI can be found in the EC table for each gain
setting.
The input capacitors can also be used to remove low frequency content from the audio signal. Small speakers cannot reproduce, and may even be damaged by low frequencies. 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 efficiency 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
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.
It is best to switch between ground and VDD for minimum
current consumption while in shutdown. The LM4674 may be
disabled with shutdown voltages in between GND and VDD,
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.
The LM4674 shutdown inputs have internal pulldown resistors. The purpose of these resistors is to eliminate any
AUDIO AMPLIFIER GAIN SETTING
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
13
G0
GAIN
V/V
dB
0
0
2
6
0
1
4
12
1
0
8
18
1
1
16
24
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LM4674
Application Information
LM4674
Application Information
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 standpoint, this is an aggressive waveform that can radiate or
conduct to other components in the system and cause interference. 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.
(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 resistance 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 increases due to higher output power, decreased load impedance 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 resistance, the use of power planes creates parasitic capacitors
that help to filter the power supply line.
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LM4674
Application Information
(Continued)
20167426
Differential Input Configuration
FIGURE 2.
15
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LM4674
Application Information
(Continued)
20167438
Single-Ended Input Configuration
FIGURE 3.
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LM4674
Revision Table
Rev
Date
Description
1.0
10/4/05
1st PDF edited after copied LM4671.
1.1
12/15/05
Added graphics 22, 23, and 24. Also did
some texts edits.
1.2
12/16/05
Edited 201674 23, then released D/S to
the WEB.
17
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LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier
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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device or system whose failure to perform can be reasonably
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