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LM4836
Stereo 2W Audio Power Amplifiers
with DC Volume Control, Bass Boost, and Input Mux
General Description
Key Specifications
The LM4836 is a monolithic integrated circuit that provides
DC volume control, and stereo bridged audio power amplifiers capable of producing 2W into 4Ω (Note 1) with less than
1.0% THD+N, or 2.2W into 3Ω (Note 2) with less than 1.0%
THD+N.
Boomer ® audio integrated circuits were designed specifically
to provide high quality audio while requiring a minimum
amount of external components. The LM4836 incorporates a
DC volume control, stereo bridged audio power amplifiers,
selectable gain or bass boost, and an input mux making it
optimally suited for multimedia monitors, portable radios,
desktop, and portable computer applications.
The LM4836 features an externally controlled, low-power
consumption shutdown mode, and both a power amplifier
and headphone mute for maximum system flexibility and
performance.
PO at 1% THD+N
into 3Ω (LM4836LQ, LM4836MTE)
into 4Ω (LM4836LQ, LM4836MTE)
into 8Ω (LM4836)
Single-ended mode - THD+N at 85mW into
32Ω
n Shutdown current
Note 1: When properly mounted to the circuit board, the LM4836LQ and
LM4836MTE will deliver 2W into 4Ω. The LM4836MT will deliver 1.1W into
8Ω. See the Application Information section for LM4836LQ and LM4836MTE
usage information.
Note 2: An LM4836LQ and LM4836MTE that have been properly mounted
to the circuit board and forced-air cooled will deliver 2.2W into 3Ω.
n
n
n
n
n
2.2W(typ)
2.0W(typ)
1.1W(typ)
1.0%(typ)
0.2µA(typ)
Features
PC98 and PC99 Compliant
DC Volume Control Interface
Input mux
System Beep Detect
Stereo switchable bridged/single-ended power amplifiers
Selectable internal/external gain and bass boost
configurable
n “Click and pop” suppression circuitry
n Thermal shutdown protection circuitry
n
n
n
n
n
n
Applications
n Portable and Desktop Computers
n Multimedia Monitors
n Portable Radios, PDAs, and Portable TVs
Connection Diagrams
LLP Package
TSSOP Package
10108802
10108883
Top View
Order Number LM4836LQ
See NS Package LQA028AA for Exposed-DAP LLP
Top View
Order Number LM4836MT or LM4836MTE
See NS Package MTC28 for TSSOP or MXA28A for
Exposed-DAP TSSOP
Boomer ® is a registered trademark of NationalSemiconductor Corporation.
© 2004 National Semiconductor Corporation
DS101088
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LM4836 Stereo 2W Audio Power Amplifiers with DC Volume Control, Bass Boost, and Input Mux
June 2002
LM4836
Absolute Maximum Ratings (Note 12)
θJC (typ) — LQA028AA
3.0˚C/W
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
θJA (typ) — LQA028AA (Note 7)
42˚C/W
θJC (typ) — MTC28
20˚C/W
θJA (typ) — MTC28
80˚C/W
Supply Voltage
6.0V
Storage Temperature
θJC (typ) — MXA28A
2˚C/W
-65˚C to +150˚C
θJA (typ) — MXA28A (Note 4)
41˚C/W
−0.3V to VDD +0.3V
θJA (typ) — MXA28A (Note 3)
54˚C/W
Power Dissipation (Note 13)
Internally limited
θJA (typ) — MXA28A (Note 5)
59˚C/W
ESD Susceptibility (Note 14)
2500V
θJA (typ) — MXA28A (Note 6)
93˚C/W
ESD Susceptibility (Note 15)
250V
Input Voltage
Junction Temperature
150˚C
Soldering Information
Vapor Phase (60 sec.)
215˚C
Infrared (15 sec.)
Operating Ratings
220˚C
See AN-450 “Surface Mounting and their Effects on
Product Reliability” for other methods of soldering surface
mount devices.
Temperature Range
TMIN ≤ TA ≤TMAX
−40˚C ≤TA ≤ 85˚C
Supply Voltage
2.7V≤ VDD ≤ 5.5V
Electrical Characteristics for Entire IC
(Notes 8, 12) The following specifications apply for VDD = 5V and TA = 25˚C unless otherwise noted.
LM4836
Symbol
Parameter
Conditions
Typical
(Note 16)
Limit
(Note 17)
Units
(Limits)
VDD
Supply Voltage
5.5
V (max)
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A
15
30
mA (max)
ISD
Shutdown Current
Vpin
0.2
2.0
µA (max)
VIH
Headphone Sense High Input Voltage
4
V (min)
VIL
Headphone Sense Low Input Voltage
0.8
V (max)
2.7
24
= VDD
V (min)
Electrical Characteristics for Volume Attenuators
(Notes 8, 12) The following specifications apply for VDD = 5V and TA = 25˚C unless otherwise noted.
LM4836
Symbol
Parameter
Conditions
Typical
(Note 16)
Limit
(Note 17)
≥ 4.5V
0
± 0.5
CRANGE
Attenuator Range
Gain with Vpin
CRANGE
Attenuator Range
Attenuation with Vpin
AM
Mute Attenuation
Vpin
3
Vpin
3
5
Units
(Limits)
dB (max)
0
−1.0
dB (min)
-73
-70
dB (min)
= 5V, Bridged Mode
-88
-80
dB (min)
= 5V, Single-Ended Mode
-80
-70
dB (min)
5
= 0V
Electrical Characteristics for Single-Ended Mode Operation
(Notes 8, 12) The following specifications apply for VDD = 5V and TA = 25˚C unless otherwise noted.
LM4836
Symbol
Parameter
Units
(Limits)
Conditions
Typical
(Note 16)
85
mW
Limit
(Note 17)
PO
Output Power
THD+N = 1.0%; f = 1kHz; RL = 32Ω
THD+N = 10%; f = 1 kHz; RL = 32Ω
95
mW
THD+N
Total Harmonic Distortion+Noise
VOUT = 1VRMS, f=1kHz, RL = 10kΩ,
AVD = 1
0.065
%
PSRR
Power Supply Rejection Ratio
CB = 1.0 µF, f =120 Hz,
VRIPPLE = 200 mVrms
58
dB
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LM4836
Electrical Characteristics for Single-Ended Mode Operation
(Continued)
(Notes 8, 12) The following specifications apply for VDD = 5V and TA = 25˚C unless otherwise noted.
LM4836
Symbol
Parameter
Conditions
SNR
Signal to Noise Ratio
POUT =75 mW, R
Filter
Xtalk
Channel Separation
f=1kHz, CB = 1.0 µF
L
Typical
(Note 16)
= 32Ω, A-Wtd
Units
(Limits)
Limit
(Note 17)
102
dB
65
dB
Electrical Characteristics for Bridged Mode Operation
(Notes 8, 12) The following specifications apply for VDD = 5V and TA = 25˚C unless otherwise noted.
LM4836
Symbol
Parameter
Conditions
Typical
(Note 16)
Limit
(Note 17)
50
Units
(Limits)
VOS
Output Offset Voltage
VIN = 0V
10
PO
Output Power
THD + N = 1.0%; f=1kHz; RL = 3Ω
(Notes 9, 11)
2.2
W
THD + N = 1.0%; f=1kHz; RL = 4Ω
(Notes 10, 11)
2
W
THD+N
Total Harmonic Distortion+Noise
mV (max)
THD = 1.5% (max);f = 1 kHz;
RL = 8Ω
1.1
1.0
W (min)
THD+N = 10%;f = 1 kHz; RL = 8Ω
1.5
W
PO = 1W, 20 Hz < f < 20 kHz,
0.3
%
RL = 8Ω, AVD = 2
PO = 340 mW, RL = 32Ω
1.0
%
PSRR
Power Supply Rejection Ratio
CB = 1.0 µF, f = 120 Hz,
VRIPPLE = 200 mVrms; RL = 8Ω
74
dB
SNR
Signal to Noise Ratio
VDD = 5V, POUT = 1.1W, RL = 8Ω,
A-Wtd Filter
93
dB
Xtalk
Channel Separation
f=1kHz, CB = 1.0 µF
70
dB
Note 3: The θJA given is for an MXA28A package whose exposed-DAP is soldered to an exposed 2in
2
piece of 1 ounce printed circuit board copper.
Note 4: The θJA given is for an MXA28A package whose exposed-DAP is soldered to a 2in2 piece of 1 ounce printed circuit board copper on a bottom side layer
through 21 8mil vias.
Note 5: The θJA given is for an MXA28A package whose exposed-DAP is soldered to an exposed 1in 2 piece of 1 ounce printed circuit board copper.
Note 6: The θJA given is for an MXA28A package whose exposed-DAP is not soldered to any copper.
Note 7: The given θJA is for an LM4836 packaged in an LQA24A with the exposed-DAP soldered to an exposed 2in2 area of 1oz printed circuit board copper.
Note 8: All voltages are measured with respect to the ground pins, unless otherwise specified. All specifications are tested using the typical application as shown
in Figure 2.
Note 9: When driving 3Ω loads and operating on a 5V supply the LM4836MTE exposed DAP must be soldered to the circuit board and forced-air cooled.
Note 10: When driving 4Ω loads and operating on a 5V supply the LM4836MTE exposed DAP must be soldered to the circuit board.
Note 11: When driving 3Ω or 4Ω loads and operating on a 5V supply, the LM4836LQ 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.
Note 12: 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 13: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θ JA, and the ambient temperature TA. The maximum
allowable power dissipation is PDMAX = (TJMAX − TA )/θJA. For the LM4836, TJMAX = 150˚C. The typical junction-to-ambient thermal resistance, when board mounted,
is 80˚C/W for the MTC28 package, 41˚C/W for the MXA28A package, and 42˚C/W for the LQA028AA package.
Note 14: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 15: Machine Model, 220 pF–240 pF discharged through all pins.
Note 16: Typicals are measured at 25˚C and represent the parametric norm.
Note 17: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
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Typical Application
FIGURE 1. Typical Application Circuit
10108803
LM4836
(Note 18)
Mute
Mux Control
HP Sense
Inputs Selected
Bridged Output
Single-Ended
Output
0
0
0
Left In 1, Right In 1
Vol. Adjustable
-
0
0
1
Left In 1, Right In 1
Muted
Vol. Adjustable
0
1
0
Left In 2, Right In 2
Vol. Adjustable
-
0
1
1
Left In 2, Right In 2
Muted
Vol. Adjustable
1
X
X
-
Muted
Muted
Note 18: If system beep is detected on the Beep in pin (pin 11) and beep is fed to inputs, the system beep will be passed through the bridged amplifier regardless
of the logic of the Mute, HP sense, or DC Volume Control pins.
Typical Performance Characteristics
MTE Specific Characteristics
LM4836MTE
THD+N vs Output Power
LM4836MTE
THD+N vs Frequency
10108871
10108870
LM4836MTE
THD+N vs Output Power
LM4836MTE
THD+N vs Frequency
10108872
10108873
5
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LM4836
Truth Table for Logic Inputs
LM4836
Typical Performance Characteristics
MTE Specific Characteristics (Continued)
LM4836MTE
Power Dissipation vs Output Power
LM4836LQ
Power Derating Curve
10108865
10108884
LM4836MTE (Note 19)
Power Derating Curve
10108864
Note 19: These curves show the thermal dissipation ability of the LM4836MTE at different ambient temperatures given these conditions:
500LFPM + 2in2: The part is soldered to a 2in2, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it.
2in2on bottom: The part is soldered to a 2in2, 1oz. copper plane that is on the bottom side of the PC board through 21 8 mil vias.
2in2: The part is soldered to a 2in2, 1oz. copper plane.
1in2: The part is soldered to a 1in2, 1oz. copper plane.
Not Attached: The part is not soldered down and is not forced-air cooled.
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LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics
THD+N vs Frequency
THD+N vs Frequency
10108857
10108858
THD+N vs Frequency
THD+N vs Frequency
10108814
10108815
THD+N vs Frequency
THD+N vs Frequency
10108816
10108817
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LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics (Continued)
THD+N vs Frequency
THD+N vs Frequency
10108818
10108819
THD+N vs Frequency
THD+N vs Frequency
10108820
10108821
THD+N vs Frequency
THD+N vs Output Power
10108824
10108822
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LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics (Continued)
THD+N vs Output Power
THD+N vs Output Power
10108825
10108826
THD+N vs Output Power
THD+N vs Output Power
10108827
10108828
THD+N vs Output Power
THD+N vs Output Power
10108830
10108829
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LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics (Continued)
THD+N vs Output Power
THD+N vs Output Power
10108831
10108832
THD+N vs Output Power
THD+N vs Output Power
10108834
10108833
THD+N vs Output Voltage
Docking Station Pins
THD+N vs Output Voltage
Docking Station Pins
10108860
10108859
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LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics (Continued)
Output Power vs
Load Resistance
Output Power vs
Load Resistance
10108862
10108806
Output Power vs
Load Resistance
Power Supply
Rejection Ratio
10108838
10108807
Output Power vs
Load Resistance
Dropout Voltage
10108853
10108808
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LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics (Continued)
Noise Floor
Noise Floor
10108842
10108841
Volume Control
Characteristics
Power Dissipation vs
Output Power
10108851
10108810
External Gain/
Bass Boost
Characteristics
Power Dissipation vs
Output Power
10108852
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10108861
12
LM4836
Typical Performance Characteristics
Non-MTE Specific Characteristics (Continued)
Power Derating Curve
Crosstalk
10108849
10108863
Output Power
vs Supply voltage
Crosstalk
10108850
10108854
Output Power
vs Supply Voltage
Supply Current
vs Supply Voltage
10108856
10108809
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LM4836
Typical Performance Characteristics
Output Power vs
Load Resistance
Output Power vs
Load Resistance
10108862
10108806
Output Power vs
Load Resistance
Power Supply
Rejection Ratio
10108838
10108807
Output Power vs
Load Resistance
Dropout Voltage
10108853
10108808
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LM4836
Typical Performance Characteristics
(Continued)
Noise Floor
Noise Floor
10108842
10108841
Volume Control
Characteristics
Power Dissipation vs
Output Power
10108851
10108810
External Gain/
Bass Boost
Characteristics
Power Dissipation vs
Output Power
10108852
10108861
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LM4836
Typical Performance Characteristics
(Continued)
Power Derating Curve
Crosstalk
10108849
10108863
Output Power
vs Supply voltage
Crosstalk
10108850
10108854
Output Power
vs Supply Voltage
Supply Current
vs Supply Voltage
10108856
10108809
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EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
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.
The LM4836’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 2.1W 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 LM4836’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 LM4836 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
LM4836MTE 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 LM4836MTE can continuously drive a 3Ω load to full
power. The LM4836LQ achieves the same output power
level without forced air cooling. In all circumstances and
conditions, the junction temperature must be held below
150˚C to prevent activating the LM4836’s thermal shutdown
protection. The LM4836’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 LQ packages are shown in
the Demonstration Board Layout section. Further detailed
and specific information concerning PCB layout, fabrication,
and mounting an LQ (LLP) package is available in National
Semiconductor’s AN1187.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4836 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 LM4836
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
AVD = 2 * (Rf/R i)
(1)
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.
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.
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
POWER DISSIPATION
Power dissipation is a major concern when
successful single-ended or bridged amplifier.
states the maximum power dissipation point
ended amplifier operating at a given supply
driving a specified output load.
PDMAX = (VDD)2/(2π2RL)
17
designing a
Equation (2)
for a singlevoltage and
Single-Ended
(2)
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LM4836
Application Information
LM4836
Application Information
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, θCS is the case-to-sink
thermal impedance, and θSA is the sink-to-ambient thermal
impedance.) Refer to the Typical Performance Characteristics curves for power dissipation information at lower output power levels.
(Continued)
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 LM4836 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 a
4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
PDMAX = 4 * (VDD)2/(2π2RL)
Bridge Mode
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 10 µF in parallel with a 0.1 µF 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 1.0 µF
tantalum bypass capacitance connected between the
LM4836’s supply pins and ground. Do not substitute a ceramic capacitor for the tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect
capacitors between the LM4836’s power supply pin and
ground as short as possible. Connecting a 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.
(3)
The LM4836’s power dissipation is twice that given by Equation (2) or Equation (3) when operating in the single-ended
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):
PDMAX' = (TJMAX − TA)/θJA
(4)
The LM4836’s TJMAX = 150˚C. In the LQ package soldered
to a DAP pad that expands to a copper area of 5in2 on a
PCB, the LM4836’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 LM4836’s θJA is 41˚C/W. At any given ambient
temperature TA, 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 LM4836’s maximum junction
temperature.
TA = TJMAX – 2*PDMAX θJA
PROPER SELECTION OF EXTERNAL COMPONENTS
Optimizing the LM4836’s performance requires properly selecting external components. Though the LM4836 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component values.
The LM4836 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.
(5)
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 LQ
package and 45˚C for the MTE package.
TJMAX = PDMAX θJA + TA
(6)
Equation (6) gives the maximum junction temperature
TJMAX. If the result violates the LM4836’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.
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
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Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (0.33µF 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, the input coupling
capacitor has an affect on the LM4835’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
18
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.
(Continued)
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 (20kΩ) and the input
capacitor produce a −3dB high pass filter cutoff frequency
that is found using Equation (7).
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, the input coupling capacitor using Equation
(7), is 0.063µF. The 0.33µF input coupling capacitor shown
in Figure 1 allows the LM4835 to drive high efficiency, full
range speaker whose response extends below 30Hz.
10108805
FIGURE 2. Resistor for Varying Output Loads
DOCKING STATION
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4836 contains circuitry that minimizes 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 LM4836’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
presents 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:
Applications such as notebook computers can take advantage of a docking station to connect to external devices such
as monitors or audio/visual equipment that sends or receives
line level signals. The LM4836 has two outputs, Pin 9 and
Pin 13, which connect to outputs of the internal input amplifiers that drive the volume control inputs. These input amplifiers can drive loads of > 1kΩ (such as powered speakers)
with a rail-to-rail signal. Since the output signal present on
the RIGHT DOCK and LEFT DOCK pins is biased to VDD/2,
coupling capacitors should be connected in series with the
load. Typical values for the coupling capacitors are 0.33µF to
1.0µF. If polarized coupling capacitors are used, connect
their "+" terminals to the respective output pin.
Since the DOCK outputs precede the internal volume control, the signal amplitude will be equal to the input signal’s
magnitude and cannot be adjusted. However, the input amplifier’s closed-loop gain can be adjusted using external
resistors. These resistors are shown in Figure 2 as 20kΩ
devices that set each input amplifier’s gain to -1. Use Equation 8 to determine the input and feedback resistor values for
a desired gain.
- A v = RF / R i
CB
(8)
TON
0.01µF
2ms
0.1µF
20ms
0.22µF
44ms
0.47µF
94ms
1.0µF
200ms
Adjusting the input amplifier’s gain sets the minimum gain for
that channel. The DOCK outputs adds circuit and functional
flexibility because their use supercedes using the inverting
outputs of each bridged output amplifier as line-level outputs.
STEREO-INPUT MULTIPLEXER (STEREO MUX)
The LM4836 has two stereo inputs. The MUX CONTROL pin
controls which stereo input is active. Applying 0V to the MUX
CONTROL pin selects stereo input 1. Applying VDD to the
MUX CONTROL pin selects stereo input 2.
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
BEEP DETECT FUNCTION
Computers and notebooks produce a system "beep" signal
that drives a small speaker. The speaker’s auditory output
signifies that the system requires user attention or input. To
19
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LM4836
Application Information
LM4836
Application Information
the LM4836’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 0.7 µA typical
shutdown current is achieved by applying a voltage that is as
near as VDD as possible to the SHUTDOWN pin. A voltage
that is less than VDD may increase the shutdown current.
Logic Level Truth Table shows the logic signal levels that
activate and deactivate micro-power shutdown and headphone amplifier operation.
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.
(Continued)
accommodate this system alert signal, the LM4836’s pin 11
is a mono input that accepts the beep signal. Internal level
detection circuitry at this input monitors the beep signal’s
magnitude. When a signal level greater than VDD/2 is detected on pin 11, the bridge output amplifiers are enabled.
The beep signal is amplified and applied to the load connected to the output amplifiers. A valid beep signal will be
applied to the load even when MUTE is active. Use the input
resistors connected between the BEEP IN pin and the stereo
input pins to accommodate different beep signal amplitudes.
These resistors are shown as 200kΩ devices in Figure 2.
Use higher value resistors to reduce the gain applied to the
beep signal. The resistors must be used to pass the beep
signal to the stereo inputs. The BEEP IN pin is used only to
detect the beep signal’s magnitude: it does not pass the
signal to the output amplifiers. The LM4836’s shutdown
mode must be deactivated before a system alert signal is
applied to BEEP IN pin.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4836’s shutdown function. Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active,
TABLE 1. Logic Level Truth Table for SHUTDOWN, HP-IN, and MUX Operation
SHUTDOWN
PIN
HP-IN PIN
MUX CHANNEL
SELECT PIN
OPERATIONAL MODE
(MUX INPUT CHANNEL #)
Logic Low
Logic Low
Logic Low
Bridged Amplifiers (1)
Logic Low
Logic Low
Logic High
Bridged Amplifiers (2)
Logic Low
Logic High
Logic Low
Single-Ended Amplifiers (1)
Logic Low
Logic High
Logic High
Single-Ended Amplifiers (2)
Logic High
X
X
Micro-Power Shutdown
MUTE FUNCTION
The LM4836 mutes the amplifier and DOCK outputs when
VDD is applied to pin 5, the MUTE pin. Even while muted, the
LM4836 will amplify a system alert (beep) signal whose
magnitude satisfies the BEEP DETECT circuitry. Applying
0V to the MUTE pin returns the LM4836 to normal, unmated
operation. Prevent unanticipated mute behavior by connecting the MUTE pin to VDD or ground. Do not let pin 5 float.
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 LM4836’s output drive
capability since the typical impedance of headphones is
32Ω.
Figure 3 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.
HP SENSE FUNCTION
Applying a voltage between 4V and VDD to the LM4836’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 3 shows the implementation of the LM4836’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
LM4836 in bridged mode operation. The output coupling
capacitor blocks the amplifier’s half supply DC voltage, protecting the headphones.
The HP-IN threshold is set at 4V. While the LM4836 operates
in bridged mode, the DC potential across the load is essentially 0V. Therefore, even in an ideal situation, the output
swing cannot cause a false single-ended trigger. Connecting
headphones to the headphone jack disconnects the headphone jack contact pin from −OUTA and allows R1 to pull the
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20
DC VOLUME CONTROL
(Continued)
The LM4836 has an internal stereo volume control whose
setting is a function of the DC voltage applied to the DC VOL
CONTROL pin. The volume control’s voltage input range is
0V to VDD. The volume range is from 0dB (DC control
voltage = 80%VDD) to -80dB (DC control voltage = 0V). The
volume remains at 0dB for DC control voltages greater than
80%VDD. When the MODE input is 0V, the LM4836 operates
at unity gain, bypassing the volume control. A graph showing
a typical volume response versus DC control voltage is
shown in the Typical Performance Characteristics section.
Like all volume controls, the LM4836’s internal volume control is set while listening to an amplified signal that is applied
to an external speaker. The actual voltage applied to the DC
VOL CONTROL pin is a result of the volume a listener
desires. As such, the volume control is designed for use in a
feedback system that includes human ears and preferences.
This feedback system operates quite well without the need
for accurate gain. The user simply sets the volume to the
desired level as determined by their ear, without regard to
the actual DC voltage that produces the volume. Therefore,
the accuracy of the volume control is not critical, as long as
the volume changes monotonically, matches well between
stereo channels, and the step size is small enough to reach
a desired volume that is not too loud or too soft. Since gain
accuracy is not critical, there will be volume variation from
part-to-part even with the same applied DC control voltage.
The gain of a given LM4836 can be set with a fixed external
voltage, but another LM4836 may require a different control
voltage to achieve the same gain. The typical part-to-part
variation can be as large as 8dB for the same control voltage.
10108804
FIGURE 3. Headphone Sensing Circuit
BASS BOOST FUNCTION
The LM4836 has a bass-boost feature that enhances the low
frequency response in applications using small speakers.
The voltage level applied to the BASS BOOST SELECT pin
controls the bass-boost function. Applying GND activates the
bass-boost mode. In bass-boost mode, the LM4836’s gain is
increased at low frequencies, with a corner frequency set by
the external capacitor, CBASS. Applying VDD defeats the
bass-boost mode and selects unity gain. Tying the BASS
BOOST SELECT pin to VDD permanently defeats the bassboost function.
Enabling bass-boost forces the output amplifiers to operate
with an internally set low frequency gain of 2 (gain of 4 in
bridged mode). The capacitor CBASS shown in Figure 1 sets
the bass-boost corner frequency. At low frequencies, the
capacitor is a virtual open circuit and the feedback resistance consists of two 10kΩ resistors. At high frequencies,
the capacitor is a virtual short circuit, which shorts one of the
two 10kΩ feedback resistors. The results is bridge amplifier
gain that increases at low frequencies. A first-order pole is
formed with a corner frequency at
fC = 1/(2π10kΩCBASS)
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8Ω Load
The following are the desired operational parameters:
Power Output:
8Ω
Input Level:
1 VRMS
Input Impedance:
Bandwidth:
20 kΩ
100 Hz−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 (11), 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 (11). The result is
Equation (12).
(9)
At f << fC, the differential gain of this bridged amplifier is
2(10kΩ + 10kΩ) /10kΩ = 4
1 WRMS
Load Impedance:
(10)
With CBASS = 0.1µF, the first-order pole has a corner frequency of 160Hz. It is assumed when using Equation 9 that
CO, Ci, fIC, and fOC, are chosen for the desired low frequency
response as explained in the Proper Selection of External
Components section. See the Typical Performance Characteristics section for a graph that includes bass-boost
performance with various values of CBASS.
(11)
VDD ≥ (VOUTPEAK+ (VODTOP + VODBOT))
21
(12)
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LM4836
Application Information
LM4836
Application Information
(Continued)
fL = 100Hz/5 = 20Hz
(15)
fH = 20kHz x 5 = 100kHz
(16)
and an
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
LM4836 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
of maximum power dissipation as explained above in the
Power Dissipation section.
As mentioned in the Selecting Proper 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 (17).
After satisfying the LM4836’s power dissipation requirements, the minimum differential gain needed to achieve 1W
dissipation in an 8Ω load is found using Equation (13).
Ci≥ 1/(2πR ifL)
(17)
The result is
1/(2π*20kΩ*20Hz) = 0.397µF
(18)
(13)
Use a 0.39µF capacitor, the closest standard value.
Thus, a minimum gain of 2.83 allows the LM4836’s to reach
full output swing and maintain low noise and THD+N performance. For this example, let AVD = 3.
The amplifier’s overall gain is set using the input (Ri) and
feedback (Ri) resistors. With the desired input impedance
set at 20kΩ, the feedback resistor is found using Equation
(14).
Rf/Ri = AVD/2
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 LM4836’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance,restricting
bandwidth limitations.
(14)
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figures 4 through 8 show the recommended four-layer PC
board layout that is optimized for the 8-pin LQ-packaged
LM4836 and associated external components. This circuit is
designed for use with an external 5V supply and 4Ω speakers.
This circuit board is 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.
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
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22
LM4836
Application Information
(Continued)
10108878
FIGURE 4. Recommended LQ PC Board Layout:
Component-Side Silkscreen
10108879
FIGURE 5. Recommended LQ PC Board Layout:
Component-Side Layout
23
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LM4836
Application Information
(Continued)
10108880
FIGURE 6. Recommended LQ PC Board Layout:
Upper Inner-Layer Layout
10108881
FIGURE 7. Recommended LQ PC Board Layout:
Lower Inner-Layer Layout
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24
LM4836
Application Information
(Continued)
10108882
FIGURE 8. Recommended LQ PC Board Layout:
Bottom-Side Layout
25
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LM4836
Physical Dimensions
inches (millimeters) unless otherwise noted
LLP Package
Order Number LM4836LQ
NS Package Number LQA028A for Exposed-DAP LLP
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26
LM4836
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
TSSOP Package
Order Number LM4836MT
NS Package Number MTC28 for TSSOP
Exposed-DAP TSSOP Package
Order Number LM4836MTE
NS Package Number MXA28A for Exposed-DAP TSSOP
27
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LM4836 Stereo 2W Audio Power Amplifiers with DC Volume Control, Bass Boost, and Input Mux
Notes
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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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
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.
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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National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship
Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned
Substances’’ as defined in CSP-9-111S2.
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