National Semiconductor LM4674 Technical data

July 2, 2008
LM4674  Filterless 2.5W Stereo Class D Audio Power Amplifier
LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier

General Description

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.
2.5W/channel of continuous output power to a 4 load with less than 10% THD+N. Flexible power supply requirements allow operation from 2.4V to 5.5V.
The LM4674 features high efficiency compared to conven­tional Class AB amplifiers. When driving an 8 speaker from a 3.6V supply, the device features 85% efficiency at PO = 500mW. Four gain options are pin selectable through the G0 and G1 pins.
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 control maximizes power savings in mixed mono/stereo applications.

Key Specifications

■ Efficiency at 3.6V, 100mW into 8Ω 80% (typ)
■ Efficiency at 3.6V, 500mW into 8Ω 85% (typ)
■ Efficiency at 5V, 1W into 8Ω 85% (typ)
■ Quiescent Power Supply Current
at 3.6V supply 4mA
■ Power Output at V
RL = 4Ω, THD 10%
■ Power Output at V
RL = 8Ω, THD 10%
■ Shutdown current
DD
DD
= 5V,
= 5V,
2.5W (typ)
1.5W (typ)
0.03μA (typ)

Features

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, and 4mm x 4mm x 0.8mm LLP packages

Applications

Mobile phones
PDAs
Laptops
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation 201674 www.national.com

Typical Application

LM4674
20167463
Ci = 1 μF CS1 = 1 μF CS2 = 0.1 μF

FIGURE 1. Typical Audio Amplifier Application Circuit

External Components Description

(Figure 1)
Components Functional Description
1. CSSupply 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. CiInput AC coupling capacitor which blocks the DC voltage at the amplifier's input terminals.
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Connection Diagrams

LM4674
TL Package (2mm x 2mm x 0.6mm)
Top View
20167461
Order Number LM4674TL
See NS Package Number TL1611A
LLP Package (4mm x 4mm x 0.8mm)
LM4674TL Markings
Top View
XY = 2 Digit date code
TT = Lot traceability
G = Boomer Family
G2 = LM4674TL
LM4674SQ Markings
20167462
Order Number LM4674SQ
Top View
See NS Package Number SQA16A
20167466
Top View
20167465
U = Wafer Fab Code
Z = Assembly Plant
XY = 2 Digit date code
TT = Lot traceability
L4674SQ = LM4674SQ
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LM4674
BUMP PIN NAME FUNCTION
A1 4 INL+ Non-inverting left channel input
A2 6 PV
DD
Power V
DD
A3 7 OUTLA Left channel output A
A4 8 OUTLB Left channel output B
B1 3 INL- Inverting left channel input
B2 5 G1 Gain setting input 1
B3 10 SDR Right channel shutdown input
B4 9 SDL Left channel shutdown input
C1 2 INR- Inverting right channel input
C2 16 G0 Gain setting input 0
C3 12 GND Ground
C4 11 PGND Power Ground
D1 1 INR+ Non-inverting right channel input
D2 15 V
DD
Power Supply
D3 14 OUTRA Right channel output A
D4 13 OUTRB Right channel output B
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LM4674

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 (T
Thermal Resistance
 θJA (μSMD)
 θJA (LLP)
JMAX
)
45.7°C/W
38.9°C/W
Supply Voltage (Note 1) 6.0V Storage Temperature −65°C to +150°C Input Voltage –0.3V to VDD +0.3V
Power Dissipation (Note 3) Internally Limited ESD Susceptibility, all other pins (Note 4) 2000V ESD Susceptibility (Note 5) 200V

Operating Ratings (Notes 1, 2)

Temperature Range
T
TA T
MIN
Supply Voltage
MAX
−40°C TA 85°C
2.4V VDD 5.5V

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 T = 25°C.
Symbol Parameter Conditions
V
OS
Differential Output Offset Voltage
VIN = 0, VDD = 2.4V to 5.0V
VIN = 0, RL = ,
I
DD
Quiescent Power Supply Current
Both channels active, VDD = 3.6V
VIN = 0, RL = , Both channels active, VDD = 5V
I
V
V
T
SD
SDIH
SDIL
WU
Shutdown Current
Shutdown Voltage Input High 1.4 V (min)
Shutdown Voltage Input Low 0.4 V (max)
Wake Up Time V
V
SDR
SDR/SDL
= V
= GND
SDL
= 0.4V 0.5 ms
G0, G1 = GND
RL =
G0 = VDD, G1 = GND
A
V
Gain
RL =
G0 = GND, G1 = V
DD
RL =
G0, G1 = V
DD
RL =
AV = 6dB
R
IN
Input Resistance
AV = 12dB
AV = 18dB
AV = 24dB
LM4674
Typical Limit
(Note 6) (Notes 7, 8)
5 mV
4 6 mA
5 7.5 mA
0.03 1
6 6 ± 0.5 dB
12 12 ± 0.5 dB
18 18 ± 0.5 dB
24 24 ± 0.5 dB
28
18.75
11.25
6.25
Units
(Limits)
150°C
A
μA
k
k
k
k
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LM4674
Symbol Parameter Conditions
LM4674
Typical Limit
(Note 6) (Notes 7, 8)
RL = 15μH + 4Ω + 15μH, THD 10% f = 1kHz, 22kHz BW
VDD = 5V 2.5
W
VDD = 3.6V 1.2 W
VDD = 2.5V 0.530 W
RL = 15μH + 8Ω + 15μH, THD 10% f = 1kHz, 22kHz BW
VDD = 5V
1.5 W
VDD = 3.6V 0.78 0.6 W
P
O
Output Power
VDD = 2.5V
RL = 15μH + 4Ω + 15μH, THD 1%
0.350
W
f = 1kHz, 22kHz BW
VDD = 5V
VDD = 3.6V
1.9 W
1
VDD = 2.5V 0.430 W
RL = 15μH + 8Ω + 15μH, THD = 1% f = 1kHz, 22kHz BW
THD+N Total Harmonic Distortion
PSRR Power Supply Rejection Ratio
VDD = 5V 1.25
VDD = 3.6V
0.63
VDD = 2.5V 0.285
PO = 500mW, f = 1kHz, RL = 8
PO = 300mW, f = 1kHz, RL = 8
V
= 200mV
RIPPLE
f
= 217Hz, Inputs AC GND,
RIPPLE
P-P
Sine,
0.07 %
0.05 %
75
Ci = 1μF, input referred
V
= 1V
RIPPLE
f
= 1kHz, Inputs AC GND,
RIPPLE
P-P
Sine,
75
W
Ci = 1μF, input referred
V
= 1V
CMRR Common Mode Rejection Ratio
η
Efficiency
Xtalk Crosstalk
SNR Signal to Noise Ratio
ε
OS
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 allowable power dissipation is P derating currents for more information.
Note 4: Human body model, 100pF discharged through a 1.5k 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.
Output Noise
DMAX
= (T
– TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4674 see power
JMAX
RIPPLE
f
RIPPLE
PO = 1W, f = 1kHz,
RL = 8Ω, VDD = 5V
PO = 500mW, f = 1kHz
VDD = 5V, PO = 1W
Input referred, A-Weighted Filter
P-P
= 217Hz
67
85
84
96
20
, θJA, and the ambient temperature, TA. The maximum
JMAX
Units
(Limits)
W
W
W
dB
dB
dB
%
dB
dB
μV
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Block Diagrams

LM4674

FIGURE 2. Differential Input Configuration

20167426
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LM4674
20167464

FIGURE 3. Single-Ended Input Configuration

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Typical Performance Characteristics

LM4674
THD+N vs Output Power
f = 1kHz, AV = 24dB, RL = 8Ω
THD+N vs Output Power
f= 1kHz, AV = 24dB, RL = 4Ω
20167439
THD+N vs Output Power
f = 1kHz, AV = 6dB, RL = 8Ω
20167440
THD+N vs Output Power
f = 1kHz, AV = 6dB, RL = 4Ω
VDD = 2.5V, P
THD+N vs Frequency
= 100mW/ch, RL = 8Ω
OUT
20167441
20167443
20167442
THD+N vs Frequency
VDD = 3.6V, P
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= 250mW/ch, RL = 8Ω
OUT
20167444
LM4674
THD+N vs Frequency
VDD = 5V, P
OUT
= 375mW/ch, RL = 8Ω
VDD = 2.5V, P
THD+N vs Frequency
= 100mW/ch, RL = 4Ω
OUT
VDD = 3.6V, P
= 250mW/ch, RL = 4Ω
OUT
Efficiency vs Output Power/channel
RL = 4Ω, f = 1kHz
THD+N vs Frequency
20167445
20167447
THD+N vs Frequency
VDD = 5V, P
= 375mW/ch, RL = 4Ω
OUT
Efficiency vs Output Power/channel
RL = 8Ω, f = 1kHz
20167446
20167448
20167449
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20167450
LM4674
Power Dissipation vs Output Power
RL = 4Ω, f = 1kHz
20167451
Output Power/channel vs Supply Voltage
RL = 4Ω, f = 1kHz
Power Dissipation vs Output Power
RL = 8Ω, f = 1kHz
20167452
Output Power/channel vs Supply Voltage
RL = 8Ω, f = 1kHz
VDD = 3.6V, V
PSRR vs Frequency
RIPPLE
= 200mV
, RL = 8Ω
P-P
20167453
20167455
20167454
Crosstalk vs Frequency
VDD = 3.6V, V
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RIPPLE
= 1V
, RL = 8Ω
P-P
20167422
LM4674
CMRR vs Frequency
VDD = 3.6V, VCM = 1V
, RL = 8Ω
P-P
Supply Current vs Supply Voltage
RL =
20167457
20167458
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Application Information

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 for each channel 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.
With the input signal applied, the duty cycle (pulse width) of the LM4674 outputs changes. For increasing output voltage, the duty cycle of the A output increases, while the duty cycle of the B output decreases for each channel. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage.

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.

POWER DISSIPATION AND EFFICIENCY

The major benefit of a Class D amplifier is increased efficiency versus a class AB amplifier. 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 (R 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.
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. For logic levels between GND and VDD bypass SD_ with a
0.1μF capacitor. The LM4674 shutdown inputs have internal pulldown resis-
tors. The purpose of these resistors is to eliminate any un-
), along with switching losses
DS(ON)
wanted 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.

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 any DC component at the input of the device. Figure 3 shows the typical single-ended applications circuit.

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.

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 high­pass filter with the input resistance Ri. The -3dB point of the high pass filter is found using Equation 1 below.
f = 1 / 2πRiC
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, 217 Hz 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.

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.
LOGIC INPUT GAIN
G1 G0 V/V dB
0 0 2 6
0 1 4 12
1 0 8 18
1 1 16 24
i
(1)
LM4674
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PCB LAYOUT GUIDELINES

As output power increases, interconnect resistance (PCB
LM4674
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.
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.
The inductive nature of the transducer load can also result in overshoot on one or 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.
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.
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LM4674TL Demo Board Schematic

LM4674
LM4674TL Demo Board Schematic
20167474
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LM4674TL Demonstration Board Layout

LM4674
Layer 1
Layer 2
20167476
20167477
Layer 3
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20167478
LM4674
Layer 4
Top Silkscreen
20167479
20167480
Bottom Silkscreen
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20167475

LM4674SQ Demo Board Schematic

LM4674
LM4674SQ Demo Board Schematic
20167481
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LM4674SQ Demonstration Board Layout

LM4674
Layer 1
Layer 2
20167485
20167483
Layer 3
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20167484
LM4674
Top Silkscreen
Bottom Layer
20167486
20167487
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Revision Table

Rev Date Description
1.0 12/16/06 Initial release.
1.1 05/17/06 Added the LLP package.
1.2 05/31/06 Added the LLP markings.
1.3 09/05/06 Added “No Load” in the Conditions on Av (3.6V table).
1.4 09/21/06 Edited graphics (26, 38, 60) and input some text edits.
1.5 09/27/06 Edited Figure 1 (page 2), TL and LLP pkg/marking drawings (page 3).
1.6 07/13/07 Added the TL and SQ demo boards and schematics diagrams.
1.7 10/30/07 Updated the SQ schematic diagram and replaced the demo boards.
1.8 07/02/08 Text edits (under SHUTDOWN FUNCTION).
LM4674
Input text edits.
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Physical Dimensions inches (millimeters) unless otherwise noted

LM4674
16 Bump micro SMD
Order Number LM4674TL
NS Package Number TLA1611A
X1 = 2mm X2 = 2mm X3 = 0.6mm
LLP Package
Order Number LM4674SQ
NS Package Number SQA16A
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Notes
LM4674
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Notes
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LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier
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