NSC LM4863

LM4863
Dual 2.2W Audio Amplifier Plus Stereo Headphone
Function
General Description
Key Specifications
The LM4863 is a dual bridge-connected audio power amplifier which, when connected to a 5V supply, will deliver 2.2W
to a 4Ω load (Note 1) or 2.5W to a 3Ω load (Note 2) with less
than 1.0% THD+N. In addition, the headphone input pin
allows the amplifiers to operate in single-ended mode when
driving stereo headphones.
n PO at 1% THD+N
n
LM4863LQ, 3Ω, 4Ω loads
2.5W(typ), 2.2W(typ)
n
LM4863MTE, 3Ω, 4Ω loads
2.5W(typ), 2.2W(typ)
n
LM4863MTE, 8Ω load
1.1W(typ)
n
LM4863, 8Ω
1.1W(typ)
n Single-ended mode THD+N at 75mW into
32Ω
0.5%(max)
n Shutdown current
0.7µA(typ)
n Supply voltage range
2.0V to 5.5V
Boomer audio power amplifiers were designed specifically to
provide high quality output power from a surface mount
package while requiring few external components. To simplify audio system design, the LM4863 combines dual bridge
speaker amplifiers and stereo headphone amplifiers on one
chip.
The LM4863 features an externally controlled, low-power
consumption shutdown mode, a stereo headphone amplifier
mode, and thermal shutdown protection. It also utilizes circuitry to reduce “clicks and pops” during device turn-on.
Note 1: An LM4863MTE or LM4863LQ that has been properly mounted to
a circuit board will deliver 2.2W into 4Ω. The other package options for the
LM4863 will deliver 1.1W into 8Ω. See the Application Information sections
for further information concerning the LM4863MTE and LM4863LQ.
Note 2: An LM4863MTE or LM4863LQ that has been properly mounted to a
circuit board and forced-air cooled will deliver 2.5W into 3Ω.
Features
Stereo headphone amplifier mode
“Click and pop” suppression circuitry
Unity-gain stable
Thermal shutdown protection circuitry
SOIC, TSSOP, exposed-DAP TSSOP, and LLP
packages
* Not recommended for new designs. Contact NSC Audio
Marketing.
n
n
n
n
n
Applications
n Multimedia monitors
n Portable and desktop computers
n Portable televisions
Typical Application
01288101
Note: Pin out shown for SO package. Refer to the Connection Diagrams for the pinout of the TSSOP, Exposed-DAP TSSOP, and Exposed-DAP LLP
packages.
Boomer ® is a registered trademark of National Semiconductor Corporation.
© 2006 National Semiconductor Corporation
DS012881
www.national.com
LM4863 Dual 2.2W Audio Amplifier Plus Stereo Headphone Function
October 2006
LM4863
Connection Diagrams
01288128
Top View
Order Number LM4863M
See NS Package Number M16B for SO
01288129
Top View
Order Number LM4863MT
See NS Package Number MTC20 for TSSOP
01288102
Top View
Order Number LM4863MTE
See NS Package Number MXA20A for Exposed-DAP
TSSOP
01288130
Top View
Order Number LM4863LQ
See NS Package Number LQA24A for Exposed-DAP LLP
* Not recommended for new designs. Contact NSC Audio Marketing.
www.national.com
2
Thermal Resistance
θJC (typ) — M16B
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
6.0V
Storage Temperature
Input Voltage
20˚C/W
θJA (typ) — M16B
80˚C/W
θJC (typ) — MTC20
20˚C/W
θJA (typ) — MTC20
80˚C/W
−65˚C to +150˚C
θJC (typ) — MXA20A
2˚C/W
−0.3V to VDD
+0.3V
θJA (typ) — MXA20A
41˚C/W (Note 7)
θJA (typ) — MXA20A
51˚C/W (Note 8)
θJA (typ) — MXA20A
90˚C/W(Note 9)
Power Dissipation (Note 4)
Internally limited
ESD Susceptibility(Note 5)
2000V
θJC (typ) — LQ24A
3.0˚C/W
ESD Susceptibility (Note 6)
200V
θJA (typ) — LQ24A
42˚C/W (Note 10)
Junction Temperature
150˚C
* Not recommended for new designs. Contact NSC Audio
Marketing.
Solder Information
Small Outline Package
Vapor Phase (60 sec.)
215˚C
Infrared (15 sec.)
220˚C
Operating Ratings
Temperature Range
See AN-450 “Surface Mounting and their Effects on
Product Reliablilty” for other methods of soldering
surface mount devices.
TMIN ≤ TA ≤ TMAX
−40˚C ≤ TA ≤ 85˚C
2.0V ≤ VDD ≤ 5.5V
Supply Voltage
Electrical Characteristics for Entire IC (Notes 3, 11)
The following specifications apply for VDD= 5V unless otherwise noted. Limits apply for TA= 25˚C.
Symbol
Parameter
VDD
Supply Voltage
IDD
Quiescent Power Supply Current
Conditions
LM4863
Typical
Limit
(Note 12)
(Note 13)
2
VIN = 0V, IO = 0A (Note 14), HP-IN = 0V
11.5
VIN = 0V, IO = 0A (Note 14), HP-IN = 4V
5.8
VDD applied to the SHUTDOWN pin
0.7
Units
(Limits)
V (min)
5.5
V (max)
20
mA (max)
6
mA (min)
mA
ISD
Shutdown Current
VIH
Headphone High Input Voltage
4
V (min)
VIL
Headphone Low Input Voltage
0.8
V (max)
2
µA (max)
Electrical Characteristics for Bridged-Mode Operation (Notes 3, 11)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25˚C.
Symbol
Parameter
Conditions
VOS
Output Offset Voltage
VIN = 0V
PO
Output Power (Note 15)
THD+N = 1%, f = 1kHz (Note 16)
LM4863MTE, RL = 3Ω
LM4863LQ, RL = 3Ω
LM4863
Typical
(Note 12)
Limit
(Note 13)
5
50
Units
(Limits)
mV (max)
2.5
2.5
W
W
LM4863MTE, RL = 4Ω
LM4863LQ, RL = 4Ω
2.2
2.2
W
W
LM4863, RL = 8Ω
1.1
1.0
W (min)
THD+N = 10%, f = 1kHz (Note 16)
LM4863MTE, RL = 3Ω
LM4863LQ, RL = 3Ω
3.2
3.2
W
W
LM4863MTE, RL = 4Ω
LM4863LQ, RL = 4Ω
2.7
2.7
W
W
3
www.national.com
LM4863
Absolute Maximum Ratings (Note 3)
LM4863
Electrical Characteristics for Bridged-Mode Operation (Notes 3, 11)
(Continued)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25˚C.
Symbol
Parameter
Conditions
LM4863
Typical
(Note 12)
LM4863, RL = 8Ω
THD+N = 1%, f = 1kHz, RL = 32Ω
THD+N
PSRR
Total Harmonic Distortion+Noise
Power Supply Rejection Ratio
Limit
(Note 13)
Units
(Limits)
1.5
W
0.34
W
20Hz ≤ f ≤ 20kHz, AVD = 2
LM4863MTE, RL = 4Ω, PO = 2W
LM4863LQ, RL = 4Ω, PO = 2W
0.3 0.3
%
LM4863, RL = 8Ω, PO = 1W
0.3
%
VDD = 5V, VRIPPLE = 200mVRMS, RL = 8Ω,
CB = 1.0µF
67
dB
XTALK
Channel Separation
f = 1kHz, CB = 1.0µF
90
dB
SNR
Signal To Noise Ratio
VDD = 5V, PO = 1.1W, RL = 8Ω
98
dB
Electrical Characteristics for Single-Ended Operation (Notes 3, 4)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25˚C.
Symbol
Parameter
Conditions
LM4863
Typical
(Note 12)
Limit
(Note 13)
Units
(Limits)
VOS
Output Offset Voltage
VIN = 0V
5
50
mV (max)
PO
Output Power
THD+N = 0.5%, f = 1kHz, RL = 32Ω
85
75
mW (min)
THD+N = 1%, f = 1kHz, RL = 8Ω
340
mW
THD+N = 10%, f = 1kHz, RL = 8Ω
440
mW
THD+N
Total Harmonic Distortion+Noise
AV = −1, PO = 75mW, 20Hz ≤ f ≤ 20kHz,
RL = 32Ω
0.2
%
PSRR
Power Supply Rejection Ratio
CB = 1.0µF, VRIPPLE = 200mV
f = 1kHz
52
dB
RMS,
XTALK
Channel Separation
f = 1kHz, CB = 1.0µF
60
dB
SNR
Signal To Noise Ratio
VDD = 5V, PO = 340mW, RL = 8Ω
95
dB
Note 3: 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 4: The maximum power dissipation is dictated by TJMAX, θ JA, and the ambient temperature TA and must be derated at elevated temperatures. The maximum
allowable power dissipation is PDMAX = (TJMAX − T A)/θJA. For the LM4863, TJMAX = 150˚C. For the θJAs for different packages, please see the Application
Information section or the Absolute Maximum Ratings section.
Note 5: Human body model, 100 pF discharged through a 1.5kΩ resistor.
Note 6: Machine model, 220pF – 240pF discharged through all pins.
Note 7: The given θJA is for an LM4863 packaged in an MXA20A with the exposed−DAP soldered to an exposed 2in2 area of 1oz printed circuit board copper.
Note 8: The given θJA is for an LM4863 packaged in an MXA20A with the exposed−DAP soldered to an exposed 1in2 area of 1oz printed circuit board copper.
Note 9: The given θJA is for an LM4863 packaged in an MXA20A with the exposed-DAP not soldered to printed circuit board copper.
Note 10: The given θJA is for an LM4863 packaged in an LQA24A with the exposed−DAP soldered to an exposed 2in2 area of 1oz printed circuit board copper.
Note 11: All voltages are measured with respect to the ground (GND) pins unless otherwise specified.
Note 12: Typicals are measured at 25˚C and represent the parametric norm.
Note 13: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 14: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
Note 15: Output power is measured at the device terminals.
Note 16: When driving 3Ω or 4Ω and operating on a 5V supply, the LM4863LQ and LM4863MTE must be mounted to the circuit board that has a minimum of 2.5in2
of exposed, uninterrupted copper area connected to the LLP package’s exposed DAP.
www.national.com
4
LM4863
Typical Performance Characteristics
MTE Specific Characteristics
LM4863MTE
THD+N vs Output Power
LM4863MTE
THD+N vs Frequency
01288199
01288197
LM4863MTE
THD+N vs Output Power
LM4863MTE
THD+N vs Frequency
01288198
01288196
LM4863MTE
Power Dissipation vs Power Output
LM4863MTE
Power Derating Curve
01288190
01288195
5
www.national.com
LM4863
Typical Performance Characteristics
MTE Specific Characteristics (Continued)
LM4863MTE (Note 17)
Power Derating Curve
01288137
Note 17: This curve shows the LM4863MTE’s thermal dissipation ability at different ambient temperatures given these conditions:
500LFPM + JEDEC board: The part is soldered to a 1S2P 20-lead exposed-DAP TSSOP test board with 500 linear feet per minute of forced-air flow across it.
Board information - copper dimensions: 74x74mm, copper coverage: 100% (buried layer) and 12% (top/bottom layers), 16 vias under the exposed-DAP.
500LFPM + 2.5in2: The part is soldered to a 2.5in2, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it.
2.5in2: The part is soldered to a 2.5in2, 1oz. copper plane.
Not Attached: The part is not soldered down and is not forced-air cooled.
Non-MTE Specific Characteristics
THD+N vs Frequency
THD+N vs Frequency
01288103
01288104
THD+N vs Frequency
THD+N vs Output Power
01288105
www.national.com
01288106
6
LM4863
Non-MTE Specific Characteristics
(Continued)
THD+N vs Output Power
THD+N vs Output Power
01288107
01288108
THD+N vs Output Power
THD+N vs Frequency
01288187
01288189
THD+N vs Output Power
THD+N vs Frequency
01288186
01288188
7
www.national.com
LM4863
Non-MTE Specific Characteristics
(Continued)
Output Power vs
Load Resistance
Power Dissipation vs
Supply Voltage
01288184
01288185
Output Power vs
Supply Voltage
Output Power vs
Supply Voltage
01288109
01288110
Output Power vs
Supply Voltage
Output Power vs
Load Resistance
01288112
01288111
www.national.com
8
LM4863
Non-MTE Specific Characteristics
(Continued)
Output Power vs
Load Resistance
Power Dissipation vs
Output Power
01288113
01288114
Dropout Voltage vs
Supply Voltage
Power Derating Curve
01288116
01288115
Power Dissipation vs
Output Power
Noise Floor
01288117
01288118
9
www.national.com
LM4863
Non-MTE Specific Characteristics
(Continued)
Channel Separation
Channel Separation
01288119
01288120
Power Supply
Rejection Ratio
Open Loop
Frequency Response
01288121
01288122
Supply Current vs
Supply Voltage
01288123
www.national.com
10
LM4863
External Components Description
(Refer to Figure 1.)
Components
Functional Description
1.
Ri
The Inverting input resistance, along with Rf, set the closed-loop gain. Ri, along with Ci, form a high pass
filter with fc = 1/(2πRiCi).
2.
Ci
The input coupling capacitor blocks DC voltage at the amplifier’s input terminals. Ci, along with Ri, create a
highpass filter with fc = 1/(2πRiCi). Refer to the section, SELECTING PROPER EXTERNAL
COMPONENTS, for an explanation of determining the value of Ci.
3.
Rf
The feedback resistance, along with Ri, set the closed-loop gain.
4.
Cs
The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING section for information about
properly placing, and selecting the value of, this capacitor.
5.
CB
The capacitor, CB, filters the half-supply voltage present on the BYPASS pin. Refer to the SELECTING
PROPER EXTERNAL COMPONENTS section for information concerning proper placement and selecting
CB’s value.
level without forced air cooling. In all circumstances and
conditions, the junction temperature must be held below
150˚C to prevent activating the LM4863’s thermal shutdown
protection. The LM4863’s power de-rating curve in the Typical Performance Characteristics shows the maximum
power dissipation versus temperature. Example PCB layouts
for the exposed-DAP TSSOP and LLP packages are shown
in the Demonstration Board Layout section. Further detailed and specific information concerning PCB layout, fabrication, and mounting an LLP package is available from
National Semiconductor’s package Engineering Group.
When contacting them, ask for "Preliminary Application Note
for the Assembly of the LLP Package on a Printed Circuit
Board, Revision A dated 7/14/00."
Application Information
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4863’s exposed-DAP (die attach paddle) packages
(MTE and LQ) provide a low thermal resistance between the
die and the PCB to which the part is mounted and soldered.
This allows rapid heat transfer from the die to the surrounding PCB copper traces, ground plane and, finally, surrounding air. The result is a low voltage audio power amplifier that
produces 2.2W at ≤ 1% THD with a 4Ω load. This high power
is achieved through careful consideration of necessary thermal design. Failing to optimize thermal design may compromise the LM4863’s high power performance and activate
unwanted, though necessary, thermal shutdown protection.
The MTE and LQ packages must have their DAPs soldered
to a copper pad on the PCB. The DAP’s PCB copper pad is
connected to a large plane of continuous unbroken copper.
This plane forms a thermal mass and heat sink and radiation
area. Place the heat sink area on either outside plane in the
case of a two-sided PCB, or on an inner layer of a board with
more than two layers. Connect the DAP copper pad to the
inner layer or backside copper heat sink area with 32(4x8)
(MTE) or 6(3x2) (LQ) vias. The via diameter should be
0.012in - 0.013in with a 1.27mm pitch. Ensure efficient thermal conductivity by plating-through and solder-filling the
vias.
Best thermal performance is achieved with the largest practical copper heat sink area. If the heatsink and amplifier
share the same PCB layer, a nominal 2.5in2 (min) area is
necessary for 5V operation with a 4Ω load. Heatsink areas
not placed on the same PCB layer as the LM4863 should be
5in2 (min) for the same supply voltage and load resistance.
The last two area recommendations apply for 25˚c ambient
temperature. Increase the area to compensate for ambient
temperatures above 25˚c. In systems using cooling fans, the
LM4863MTE can take advantage of forced air cooling. With
an air flow rate of 450 linear-feet per minute and a 2.5in2
exposed copper or 5.0in2 inner layer copper plane heatsink,
the LM4863MTE can continuously drive a 3Ω load to full
power. The LM4863LQ achieves the same output power
PCB LAYOUT AND SUPPLY REGULATION
CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω LOADS
Power dissipated by a load is a function of the voltage swing
across the load and the load’s impedance. As load impedance decreases, load dissipation becomes increasingly dependent on the interconnect (PCB trace and wire) resistance
between the amplifier output pins and the load’s connections. Residual trace resistance causes a voltage drop,
which results in power dissipated in the trace and not in the
load as desired. For example, 0.1Ω trace resistance reduces
the output power dissipated by a 4Ω load from 2.1W to 2.0W.
This problem of decreased load dissipation is exacerbated
as load impedance decreases. Therefore, to maintain the
highest load dissipation and widest output voltage swing,
PCB traces that connect the output pins to a load must be as
wide as possible.
Poor power supply regulation adversely affects maximum
output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply
voltage causes decreased headroom, output signal clipping,
and reduced output power. Even with tightly regulated supplies, trace resistance creates the same effects as poor
supply regulation. Therefore, making the power supply
traces as wide as possible helps maintain full output voltage
swing.
11
www.national.com
LM4863
Application Information
(Continued)
01288101
* Refer to the section Proper Selection of External Components, for a detailed discussion of CB size.
FIGURE 1. Typical Audio Amplifier Application Circuit
Pin out shown for the SO package. Refer to the Connection Diagrams for the pinout of the TSSOP, Exposed-DAP
TSSOP, and Exposed-DAP LLP packages.
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply, singleended amplifiers require. Eliminating an output coupling capacitor in a single-ended configuration forces a single-supply
amplifier’s half-supply bias voltage across the load. This
increases internal IC power dissipation and may permanently damage loads such as speakers.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4863 consists of two pairs of
operational amplifiers, forming a two-channel (channel A and
channel B) stereo amplifier. (Though the following discusses
channel A, it applies equally to channel B.) External resistors
Rf and Ri set the closed-loop gain of Amp1A, whereas two
internal 20kΩ resistors set Amp2A’s gain at -1. The LM4863
drives a load, such as a speaker, connected between the two
amplifier outputs, -OUTA and +OUTA.
Figure 1 shows that Amp1A’s output serves as Amp2A’s
input. This results in both amplifiers producing signals identical in magnitude, but 180˚ out of phase. Taking advantage
of this phase difference, a load is placed between -OUTA
and +OUTA and driven differentially (commonly referred to
as "bridge mode"). This results in a differential gain of
(1)
AVD = 2 x (Rf / Ri)
Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a single amplifier’s output and ground. For a given supply voltage, bridge
mode has a distinct advantage over the single-ended configuration: its differential output doubles the voltage swing
across the load. This produces four times the output power
when compared to a single-ended amplifier under the same
conditions. This increase in attainable output power assumes that the amplifier is not current limited or that the
output signal is not clipped. To ensure minimum output signal clipping when choosing an amplifier’s closed-loop gain,
refer to the Audio Power Amplifier Design section.
www.national.com
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. Equation (2)
states the maximum power dissipation point for a singleended amplifier operating at a given supply voltage and
driving a specified output load
(2)
PDMAX = (VDD)2 / (2π2 RL) Single-Ended
However, a direct consequence of the increased power delivered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.
The LM4863 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended amplifier. From Equation (3), assuming a 5V power supply and an
4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
(3)
PDMAX = 4 x (VDD)2 / (2π2 RL) Bridge Mode
The LM4973’s power dissipation is twice that given by Equation (2) or Equation (3) when operating in the single-ended
12
1µF capacitor, CB, between the BYPASS pin and ground
improves the internal bias voltage’s stability and improves
the amplifier’s PSRR. The PSRR improvements increase as
the bypass pin capacitor value increases. Too large, however, increases turn-on time and can compromise amplifier’s
click and pop performance. The selection of bypass capacitor values, especially CB, depends on desired PSRR requirements, click and pop performance (as explained in the section, Proper Selection of External Components), system
cost, and size constraints.
(Continued)
mode or bridge mode, respectively. Twice the maximum
power dissipation point given by Equation (3) must not exceed the power dissipation given by Equation (4):
(4)
PDMAX’ = (TJMAX − TA) / θJA
The LM4863’s TJMAX = 150˚C. In the LQ (LLP) package
soldered to a DAP pad that expands to a copper area of 5in2
on a PCB, the LM4863’s θJA is 20˚C/W. In the MTE package
soldered to a DAP pad that expands to a copper area of 2in2
on a PCB , the LM4863’s θJA is 41˚C/W. At any given
ambient temperature TJ\A, use Equation (4) to find the maximum internal power dissipation supported by the IC packaging. Rearranging Equation (4) and substituting PDMAX for
PDMAX’ results in Equation (5). This equation gives the
maximum ambient temperature that still allows maximum
stereo power dissipation without violating the LM4863’s
maximum junction temperature.
(5)
TA = TJMAX − 2 x PDMAX θJA
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4863’s shutdown function. Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active,
the LM4863’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically VDD/2. The low 0.7µA typical
shutdown current is achieved by applying a voltage that is as
near as VDD as possible to the SHUTDOWN pin. A voltage
thrat is less than VDD may increase the shutdown current.
For a typical application with a 5V power supply and an 4Ω
load, the maximum ambient temperature that allows maximum stereo power dissipation without exceeding the maximum junction temperature is approximately 99˚C for the LLP
package and 45˚C for the MTE package.
(6)
TJMAX = PDMAX θJA + TA
Equation (6) gives the maximum junction temperature TJMAX. If the result violates the LM4863’s 150˚C, reduce the
maximum junction temperature by reducing the power supply voltage or increasing the load resistance. Further allowance should be made for increased ambient temperatures.
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 10kΩ pull-up resistor between the
SHUTDOWN pin and VDD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier operation by closing the switch. Opening the switch connects the
SHUTDOWN pin to VDD through the pull-up resistor, activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN pin will not float. This prevents
unwanted state changes. In a system with a microprocessor
or a 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.
The above examples assume that a device is a surface
mount part operating around the maximum power dissipation
point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of Equation (2) is greater than that of Equation
(3), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to
reduce θJA. The heat sink can be created using additional
copper area around the package, with connections to the
ground pin(s), supply pin and amplifier output pins. External,
solder attached SMT heatsinks such as the Thermalloy
7106D can also improve power dissipation. When adding a
heat sink, the θJA is the sum of θJC, θCS, and θSA. (θJC is the
junction−to−case thermal impedance, CS is the case−to−sink
thermal impedance, and θSAis the sink−to−ambient thermal
impedance.) Refer to the Typical Performance Characteristics curves for power dissipation information at lower output
power levels.
TABLE 1. Logic level truth table for SHUTDOWN and
HP-IN Operation
SHUTDOWN
HP-IN PIN
Low
logic Low
OPERATIONAL MODE
Bridged amplifiers
Low
logic High
Single-Ended amplifiers
High
logic Low
Micro-power Shutdown
High
logic High
Micro-power Shutdown
HP-IN FUNCTION
Applying a voltage between 4V and VDD to the LM4863’s
HP-IN headphone control pin turns off Amp2A and Amp2B,
muting a bridged-connected load. Quiescent current consumption is reduced when the IC is in this single-ended
mode.
Figure 2 shows the implementation of the LM4863’s headphone control function. With no headphones connected to
the headphone jack, the R1-R2 voltage divider sets the
voltage applied to the HP-IN pin (pin 16) at approximately
50mV. This 50mV enables Amp1B and Amp2B, placing the
LM4863’s in bridged mode operation. The output coupling
capacitor blocks the amplifier’s half-supply DC voltage, protecting the headphones.
While the LM4863 operates in bridged mode, the DC potential across the load is essentially 0V. The HP-IN threshold is
set at 4V. Therefore, even in an ideal situation, the output
swing cannot cause a false single-ended trigger. Connecting
headphones to the headphone jack disconnects the head-
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 5V regulator typically
use a 10µF in parallel with a 0.1µF filter capacitors to stabilize the regulator’s output, reduce noise on the supply line,
and improve the supply’s transient response. However, their
presence does not eliminate the need for a local 1.0µF
tantalum bypass capacitance connected between the
LM4863’s supply pins and ground. Do not substitute a ceramic capacitor for the tantalum. Doing so may cause oscillation in the output signal. Keep the length of leads and
traces that connect capacitors between the LM4863’s power
supply pin and ground as short as possible. Connecting a
13
www.national.com
LM4863
Application Information
LM4863
Application Information
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (Ci in Figure 1). A high value capacitor can be expensive and may compromise space efficiency
in portable designs. In many cases, however, the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with this limited frequency response reap
little improvement by using large input capacitor.
Besides effecting system cost and size, Ci has an affect on
the LM4863’s click and pop performance. When the supply
voltage is first applied, a transient (pop) is created as the
charge on the input capacitor changes from zero to a quiescent state. The magnitude of the pop is directly proportional
to the input capacitor’s size. Higher value capacitors need
more time to reach a quiescent DC voltage (usually VDD/2)
when charged with a fixed current. The amplifier’s output
charges the input capacitor through the feedback resistor,
Rf. Thus, pops can be minimized by selecting an input
capacitor value that is no higher than necessary to meet the
desired -3dB frequency.
A shown in Figure 1, the input resistor (RI) and the input
capacitor, CI produce a −3dB high pass filter cutoff frequency
that is found using Equation (7).
(Continued)
phone jack contact pin from -OUTA and allows R1 to pull the
HP Sense pin up to VDD. This enables the headphone function, turns off Amp2A and Amp2B, and mutes the bridged
speaker. The amplifier then drives the headphones, whose
impedance is in parallel with resistor R2 and R3. These
resistors have negligible effect on the LM4863’s output drive
capability since the typical impedance of headphones is
32Ω.
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, CI, using Equation (4), is 0.063µF. The 1.0µF
CI shown in Figure 1 allows the LM4863 to drive high efficiency, full range speaker whose response extends below
30Hz.
01288124
FIGURE 2. Headphone Circuit
Figure 2 also shows the suggested headphone jack electrical connections. The jack is designed to mate with a threewire plug. The plug’s tip and ring should each carry one of
the two stereo output signals, whereas the sleeve should
carry the ground return. A headphone jack with one control
pin contact is sufficient to drive the HP-IN pin when connecting headphones.
A microprocessor or a switch can replace the headphone
jack contact pin. When a microprocessor or switch applies a
voltage greater than 4V to the HP-IN pin, a bridge-connected
speaker is muted and Amp1A and Amp2A drive a pair of
headphones.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consideration should be paid to value of CB, the capacitor connected to the BYPASS pin. Since CB determines how fast
the LM4863 settles to quiescent operation, its value is critical
when minimizing turn−on pops. The slower the LM4863’s
outputs ramp to their quiescent DC voltage (nominally 1/2
VDD), the smaller the turn−on pop. Choosing CB equal to
1.0µF along with a small value of Ci (in the range of 0.1µF to
0.39µF), 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.
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4863’s performance requires properly selecting external components. Though the LM4863 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component values.
The LM4863 is unity-gain stable, giving a designer maximum
design flexibility. The gain should be set to no more than a
given application requires. This allows the amplifier to
achieve minimum THD+N and maximum signal-to-noise ratio. These parameters are compromised as the closed-loop
gain increases. However, low gain demands input signals
with greater voltage swings to achieve maximum output
power. Fortunately, many signal sources such as audio CODECs have outputs of 1VRMS (2.83VP-P). Please refer to the
Audio Power Amplifier Design section for more information on selecting the proper gain.
www.national.com
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4863 contains circuitry to minimize turn-on and shutdown transients or "clicks and pop". For this discussion,
turn-on refers to either applying the power supply voltage or
when the shutdown mode is deactivated. While the power
supply is ramping to its final value, the LM4863’s internal
amplifiers are configured as unity gain buffers. An internal
current source changes the voltage of the BYPASS pin 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 1/2 VDD. As soon as the voltage on the
BYPASS pin is stable, the device becomes fully operational.
Although the bypass pin current cannot be modified, changing the size of CB alters the device’s turn-on time and the
magnitude of "clicks and pops". Increasing the value of CB
reduces the magnitude of turn-on pops. However, this pre14
LM4863 to produce peak output power in excess of 1W
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
maximum power dissipation as explained above in the
Power Dissipation section.
After satisfying the LM4863’s power dissipation requirements, the minimum differential gain is found using Equation
(10).
(Continued)
sents a tradeoff: as the size of CB increases, the turn-on time
increases. There is a linear relationship between the size of
CB and the turn-on time. Here are some typical turn-on times
for various values of CB:
CB
TON
0.01µF
20 ms
0.1µF
200 ms
0.22µF
440 ms
(10)
0.47µF
940 ms
1.0µF
2 Sec
Thus, a minimum gain of 2.83 allows the LM4863’s to reach
full output swing and maintain low noise and THD+N performance. For this example, let AVD = 3.
In order eliminate "clicks and pops", all capacitors must be
discharged before turn-on. Rapidly switching VDD may not
allow the capacitors to fully discharge, which may cause
"clicks and pops". In a single-ended configuration, the output
is coupled to the load by COUT. This capacitor usually has a
high value. COUT discharges through internal 20kΩ resistors.
Depending on the size of COUT, the discharge time constant
can be relatively large. To reduce transients in single-ended
mode, an external 1kΩ - 5kΩ resistor can be placed in
parallel with the internal 20kΩ resistor. The tradeoff for using
this resistor is increased quiescent current.
The amplifier’s overall gain is set using the input (Ri) and
feedback (Rf) resistors. With the desired input impedance
set at 20kΩ, the feedback resistor is found using Equation
(11).
(11)
Rf/Ri = AVD/2
The value of Rf is 30kΩ.
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
(12)
fL = 100Hz/5 = 20Hz
and an
FH = 20kHzx5 = 100kHz
(13)
NO LOAD STABILITY
The LM4863 may exhibit low level oscillation when the load
resistance is greater than 10kΩ. This oscillation only occurs
as the output signal swings near the supply voltages. Prevent this oscillation by connecting a 5kΩ between the output
pins and ground.
As mentioned in the 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 (12).
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8Ω Load
The following are the desired operational parameters:
Power Output:
Load Impedance:
Input Level:
Input Impedance:
Bandwidth:
1Wrms
8Ω
1Vrms
the result is
20kΩ
1/(2π*20kΩ*20Hz) = 0.398µF
(14)
Use a 0.39µF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain, AVD, determines the
upper passband response limit. With AVD = 3 and fH =
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4863’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance-lrestricting
bandwidth limitations.
100Hz−20 kHz ± 0.25 dB
The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the Typical Performance Characteristics section. Another way, using Equation (4), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To account for the amplifier’s dropout voltage, two additional voltages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics curves, must be
added to the result obtained by Equation (8). The result in
Equation (9).
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figures 3 through 6 show the recommended two-layer PC
board layout that is optimized for the 20-pin MTE-packaged
LM4863 and associated external components. Figures 7
through 11 show the recommended four-layer PC board
layout that is optimized for the 24-pin LQ-packaged LM4863
and associated external components. These circuits are designed for use with an external 5V supply and 4Ω speakers.
These circuit boards are easy to use. Apply 5V and ground to
the board’s VDD and GND pads, respectively. Connect 4Ω
speakers between the board’s -OUTA and +OUTA and
OUTB and +OUTB pads.
(8)
(9)
VDD ≥ (VOUTPEAK + (VODTOP + VODBOT))
The Output Power vs Supply Voltage graph for an 8Ω load
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
15
www.national.com
LM4863
Application Information
LM4863
Application Information
(Continued)
01288192
01288194
FIGURE 6. Recommended MTE PC board layout:
bottom-side layout
FIGURE 3. MTE PC board layout:
all layers superimposed
01288193
01288131
FIGURE 4. MTE PC board layout:
Component-side Silkscreen
FIGURE 7. Recommended LQ PC board layout:
Component-side Silkscreen
01288191
FIGURE 5. Recommended MTE PC board layout:
Component-side layout
www.national.com
16
LM4863
Application Information
(Continued)
01288134
01288132
FIGURE 10. Recommended LQ PC board layout:
lower inner-layer layout
FIGURE 8. Recommended LQ PC board layout:
Component-side layout
01288135
01288133
FIGURE 11. Recommended LQ PC board layout:
bottom-side layout
FIGURE 9. Recommended LQ PC board layout:
upper inner-layer layout
17
www.national.com
LM4863
Revision History
Rev
1.1
www.national.com
Date
Description
10/30/06
Removed all references to the 16–lead plastic-DIP
package.
18
LM4863
Physical Dimensions
inches (millimeters) unless otherwise noted
16-Lead (0.300" Wide) Molded Small Outline Package, JEDEC
Order Number LM4863M
NS Package Number M16B
20-Lead Molded PKG, TSSOP, JEDEC, 4.4mm BODY WIDTH
Order Number LM4863MT
NS Package Number MTC20
19
www.national.com
LM4863
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
20-Lead Molded TSSOP, Exposed Pad, 6.5x4.4x0.9mm
Order Number LM4863MTE
NS Package Number MXA20A
24-Lead Molded pkg, Leadframe Package LLP
Order Number LM4863LQ
NS Package Number LQA24A
www.national.com
20
THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION
(″NATIONAL″) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR
COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO
SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED,
ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT.
TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT
NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL
PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS
ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING
NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS,
BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS.
EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO
LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND/OR
USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE,
MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR
SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL
OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
Life support devices or systems are devices 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. A critical component is any component in 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 and the National Semiconductor logo are trademarks or registered trademarks of National Semiconductor
Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders.
Copyright © 2006 National Semiconductor Corporation.
For the most current product information visit us at www.national.com.
National Semiconductor
Americas Customer
Support Center
Email: new.[email protected]
Tel: 1-800-272-9959
www.national.com
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Email: [email protected]
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: [email protected]
Tel: 81-3-5639-7560
LM4863 Dual 2.2W Audio Amplifier Plus Stereo Headphone Function
Notes