LM4915 - Octopart

LM4915 - Octopart
LM4915
LM4915 Pseudo-Differential Mono Headphone Amplifier with Fixed 6dB Gain
Literature Number: SNAS176
LM4915
Pseudo-Differential Mono Headphone Amplifier with
Fixed 6dB Gain
General Description
Key Specifications
The LM4915 is a pseudo-differential audio power amplifier
primarily designed for demanding applications in mobile
phones and other portable audio device applications with
mono headphones. It is capable of delivering 90 miliwatts of
continuous average power to a 32Ω BTL load with less than
1% distortion (THD+N) from a 3VDC power supply.
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Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4915 does not require output
coupling capacitors or bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement.
The LM4915 features a low-power consumption shutdown
mode. To facilitate this, Shutdown may be enabled by driving
the shutdown pin low. Additionally, the LM4915 features an
internal thermal shutdown protection mechanism.
The LM4915 contains advanced pop & click circuitry which
virtually eliminates noises which would otherwise occur during turn-on and turn-off transitions.
The LM4915 has an internally fixed gain of 6dB.
Improved PSRR at 217Hz and 1kHz
75dB (typ)
Power Output at 5.0V & 1% THD into 32Ω 280mW (typ)
Power Output at 3.0V & 1% THD into 32Ω 90mW (typ)
Output Noise, A-weighted
20µV (typ)
Features
Pseudo-differential amplification
Internal gain-setting resistors
Available in space-saving LLP package
Ultra low current shutdown mode
Can drive capacitive loads up to 500pF
Improved pop & click circuitry virtually eliminates noises
during turn-on and turn-off transitions
n 2.2 - 5.5V operation
n No output coupling capacitors, snubber networks,
bootstrap capacitors or gain-setting resistors required
n Ultra low noise
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n
n
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Applications
n Mobile phones
n PDAs
n Portable electronics devices
Typical Application
200482B4
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer ® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation
DS200482
www.national.com
LM4915 Pseudo-Differential Mono Headphone Amplifier with Fixed 6dB Gain
May 2003
LM4915
Connection Diagrams
LQ Package
200482B5
Top View
Order Number LM4915LQ
See NS Package Number LQB08A
8 Pin LQ Marking
200482E7
X - Date Code
TT - Die Traceability
G - Boomer
A5 - LM4915LQ
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2
Junction Temperature
(Note 2)
Thermal Resistance
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
150˚C
θJC (LQ)
57˚C/W
θJA (LQ)
140˚C/W
6.0V
Storage Temperature
−65˚C to +150˚C
Operating Ratings
-0.3V to VDD + 0.3V
Input Voltage
Temperature Range
Power Dissipation (Note 3)
Internally Limited
ESD Susceptibility (Note 4)
2000V
TMIN ≤ TA ≤ TMAX
200V
Supply Voltage (VDD)
ESD Susceptibility (Note 5)
−40˚C ≤ TA ≤ +85˚C
2.2V ≤ VCC ≤ 5.5V
Electrical Characteristics VDD = 5V (Notes 1, 2, 8)
The following specifications apply for VDD = 5V, RL = 16Ω unless otherwise specified. Limits apply to TA = 25˚C.
Symbol
Parameter
Conditions
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A
VSHUTDOWN = GND
LM4915
Units
(Limits)
Typ
(Note 6)
Limit
(Note 7)
2
3.5
mA (max)
0.1
Note 9
µA(max)
ISD
Shutdown Current
VSDIH
Shutdown Voltage Input High
1.8
V
VSDIL
Shutdown Voltage Input Low
0.4
V
PO
Output Power
THD = 1% (max); f = 1kHz
RL = 16
RL = 32
400
280
VNO
Output Noise Voltage
BW = 20Hz to 20kHz, A-weighted
20
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mV sine p-p
75
VOS
Output Offset Voltage
VIN = 0V
2
375
250
mW
µV
dB
20
mV (max)
Electrical Characteristics VDD = 3.0V (Notes 1, 2, 8)
The following specifications apply for VDD = 3.0V, RL = 16Ω unless otherwise specified. Limits apply to TA = 25˚C.
Symbol
Parameter
Conditions
LM4915
Typ
(Note 6)
Limit
(Note 7)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A
1.5
2.5
mA (max)
ISD
Shutdown Current
VSHUTDOWN = GND
0.1
Note 9
µA(max)
VSDIH
Shutdown Voltage Input High
VSDIL
Shutdown Voltage Input Low
PO
Output Power
1.8
V
0.4
V
THD = 1% (max); f = 1kHz
RL = 16
RL = 32
125
90
VNO
Output Noise Voltage
BW = 20Hz to 20kHz, A-weighted
20
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mV sine p-p
70
VOS
Output Offset Voltage
VIN = 0V
2
100
80
mW (min)
µV
dB
20
mV (max)
Note 1: All voltages are measured with respect to the GND pin unless otherwise specified.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature, TA. The maximum
allowable power dissipation is PDMAX = (TJMAX - TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4915, see power derating
curves for more information.
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 5: Machine Model, 220pF-240pF discharged through all pins.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Datasheet min/max specifications are guaranteed by design, test, or statistical analysis.
3
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LM4915
Absolute Maximum Ratings
LM4915
Electrical Characteristics VDD = 3.0V (Notes 1, 2, 8)
(Continued)
Note 9: See ISD distribution values shown in the ISD Distribution curve, VDD = 5V and V = 3V, shown in the Typical Performance Characteristics section.
External Components Description
Components
(Figure 1)
Functional Description
1.
CB
Bypass pin capacitor that provides half-supply filtering. Refer to the section Proper Selection of External
Components for information concerning proper placement and selection of CB.
2.
Ci
Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a
high-pass filter with the internal input resistance Ri. For the LM4915, Ri = 20kΩ, thus creating a high-pass
filter fc = 1/(2πRiCi). Refer to the section Proper Selection of External Components for an explanantion of
how to determine the value of Ci.
Typical Performance Characteristics
THD+N vs Frequency
VDD = 5V, RL = 32Ω
THD+N vs Frequency
VDD = 5V, RL = 16Ω
200482C6
200482C7
THD+N vs Frequency
VDD = 3V, RL = 32Ω, PO = 80mW
THD+N vs Frequency
VDD = 3V, RL = 16Ω, PO = 100mW
200482C4
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200482C5
4
LM4915
Typical Performance Characteristics
(Continued)
THD+N vs Frequency
VDD = 2.6V, RL = 16Ω, PO = 50mW
THD+N vs Frequency
VDD = 2.6V, RL = 32Ω, PO = 40mW
200482C2
200482C3
THD+N vs Output Power
VDD = 5V, RL = 32Ω
THD+N vs Output Power
VDD = 5V, RL = 16Ω
200482D2
200482D3
THD+N vs Output Power
VDD = 3V, RL = 32Ω
THD+N vs Output Power
VDD = 3V, RL = 16Ω
200482D0
200482D1
5
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LM4915
Typical Performance Characteristics
(Continued)
THD+N vs Output Power
VDD = 2.6V, RL = 16Ω
THD+N vs Output Power
VDD = 2.6V, RL = 32Ω
200482C8
200482C9
PSRR vs Frequency
VDD = 5V, RL = 32Ω, PO = 250mW
Input 10Ω Terminated
PSRR vs Frequency
VDD = 5V, RL = 16Ω, PO = 375mW
Input 10Ω Terminated
200482C0
200482C1
PSRR vs Frequency
VDD = 3V, RL = 32Ω
Input 10Ω Terminated
PSRR vs Frequency
VDD = 3V, RL = 16Ω
Input 10Ω Terminated
200482B8
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200482B9
6
LM4915
Typical Performance Characteristics
(Continued)
PSRR vs Frequency
VDD = 2.6V, RL = 16Ω
Input 10Ω Terminated
PSRR vs Frequency
VDD = 2.6V, RL = 32Ω
Input 10Ω Terminated
200482B6
200482B7
Output Power vs Supply Voltage
RL = 16Ω
Output Power vs Load Resistance
VDD = 2.6V, RL = 32Ω
200482D9
200482E5
Power Dissipation vs Output Power
VDD = 5V
Output Power vs Supply Voltage
RL = 32Ω
200482E4
200482E1
7
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LM4915
Typical Performance Characteristics
(Continued)
Power Dissipation vs Output Power
VDD = 3V
Frequency Response
vs Input Capacitor Size
200482E0
200482E6
Noise Floor
Shutdown Hysterisis Voltage
VDD = 5V
200482E8
200482D8
ISD Distribution
VDD = 5V
Shutdown Hysterisis Voltage
VDD = 3V
200482E9
200482F0
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8
LM4915
Typical Performance Characteristics
(Continued)
ISD Distribution
VDD = 3V
200482F1
figuration, the half-supply bias across the load would result
in both increased internal IC power dissipation as well as
permanent loudspeaker damage.
Application Information
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4915 is a pseudo-differential audio amplifier that
features a fixed gain of 6dB. Internally this is accomplished
by two separate sets of inverting amplifiers, each set to a
gain of 2. The LM4915 features precisely matched internal
gain-setting resistors set to Ri = 20kΩ and Rf = 40kΩ, thus
eliminating the need for external resistors and fixing the
differential gain at AVD = 6dB.
A differential amplifier works in a manner where the difference between the two input signals is amplified. In most
applications, this would require input signals that are 180˚
out of phase with each other. The LM4915 works in a
pseudo-differential manner, so DC offset normally cancelled
by a fully differential amplifier needs to be blocked by input
coupling capacitors for the LM4915 to amplify the difference
between the inputs.
The LM4915 provides what is known as a ’bridged mode’
output (bridge-tied-load, BTL). This results in output signals
at Vo1 and Vo2 that are 180˚ out of phase with respect to
each other. Bridged mode operation is different from the
single-ended amplifier configuration that connects the load
between the amplifier output and ground. A bridged amplifier
design has distinct advantages over the single-ended configuration: it provides differential drive to the load, thus doubling maximum possible output swing for a specific supply
voltage. Four times the output power is possible compared
with a single-ended amplifier under the same conditions.
This increase in attainable output power assumes that the
amplifier is not current limited or clipped. A bridged configuration, such as the one used in the LM4915, also creates a
second advantage over single-ended amplifiers. Since the
differential outputs, Vo1 and Vo2 , are biased at half-supply,
no net DC voltage exists across the load. BTL configuration
eliminates the output coupling capacitor required in singlesupply, single-ended amplifier configurations. If an output
coupling capacitor is not used in a single-ended output con-
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifer, whether the amplifier is bridged or
single-ended. Equation 1 states the maximum power dissipation point for a single-ended amplifier operating at a given
supply voltage and driving a specified output load.
PDMAX = (VDD)
2
/ (2π2RL)
Single-Ended
(1)
However, a direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in
internal power dissipation versus a single-ended amplifier
operating at the same conditions.
PDMAX = 4(VDD)
2
/ (2π2RL)
Bridge Mode
(2)
Since the LM4915 has bridged outputs, the maximum internal power dissipation is 4 times that of a single-ended amplifier.
Even with this substantial increase in power dissipation, the
LM4915 does not require additional heatsinking under most
operating conditions and output loading. From Equation 2,
assuming a 5V power supply and an 16Ω load, the maximum
power dissipation point is 316mW. The maximum power
dissipation point obtained from Equation 2 must not be
greater than the power dissipation results from Equation 3:
PDMAX = (TJMAX - TA) / θJA
(3)
The LM4915’s θJA in an LQB08A package is 140˚C/W. Depending on the ambient temperature, TA , of the system
surroundings, Equation 3 can be used to find the maximum
internal power dissipation supported by the IC packaging. If
the result of Equation 2 is greater than that of Equation 3,
9
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LM4915
Application Information
The switch and resistor guarantee that the SHUTDOWN pin
will not float. This prevents unwanted state changes. In a
system with a microprocessor or 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)
then either the supply voltage must be decreased, the load
impedance increased, the ambient temperature reduced, or
the θJA reduced with heatsinking. In many cases, larger
traces near the output, VDD, and GND pins can be used to
lower the θJA. The larger areas of copper provide a form of
heatsinking allowing higher power dissipation. For the typical
application of a 5V power supply, with a 16Ω load power
dissipation is not an issue. Recall that internal power dissipation is a function of output power. If typical operation is not
around the maximum power dissipation point, the LM4915
can operate at higher ambient temperatures. Refer to the
Typical Performance Characteristics curves for power dissipation information.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is critical to optimize device
and system performance. While the LM4915 is tolerant of
external component combinations, and requires minimal external components, consideration to component values must
be used to maximize overall system quality.
The input coupling capacitor, Ci, forms a first order high pass
filter which limits low frequency response given by fc =
1/(2πRiCi). Ri is internally set to 20kΩ. This value should be
chosen based on needed frequency response for a few
distinct reasons.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor location on both the
bypass and power supply pins should be as close to the
device as possible. A larger half-supply bypass capacitor
improves PSRR because it increases half-supply stability.
Selection of Input Capacitor Size
Large input capacitors are both expensive and space hungry
for portable designs. Clearly, a certain sized capacitor is
needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable
systems, whether internal or external, have little ability to
reproduce signals below 100Hz to 150Hz. Thus, using a
large input capacitor may not increase actual system performance.
In addition to system cost and size, click and pop performance is affected by the size of the input coupling capacitor,
CI. A larger input coupling capacitor requires more charge to
reach its quiescent DC voltage (nominally 1/2 VDD). This
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the
capacitor size based on necessary low frequency response,
turn-on pops can be minimized
Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value. Bypass
capacitor, CB, is the most critical component to minimize
turn-on pops since it determines how fast the LM4915 turns
on. The slower the LM4915’s outputs ramp to their quiescent
DC voltage (nominally 1/2 VDD), the smaller the turn-on pop.
Choosing CB equal to 4.7µF along with a small value of CI (in
the range of 0.1µF to 0.47µF), should produce a virtually
clickless and popless shutdown function. While the device
will function properly, (no oscillations or motorboating), with
CB equal to 1.0µF, the device will be much more susceptible
to turn-on clicks and pops. Thus, a value of CB equal to
4.7µF is recommended in all but the most cost sensitive
designs.
Typical applications employ a 5V regulator with 10µF and
0.1µF bypass capacitors that increase supply stability. This,
however, does not eliminate the need for bypassing the
supply nodes of the LM4915. A 1µF capacitor is recommended for CS. A 4.7µF capacitor is recommended for CB.
This value coupled with small input capacitors (0.1µF to
0.47µF) gives virtually zero click and pop with outstanding
PSRR performance.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4915’s shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHUTDOWN
pin. When active, the LM4915’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The trigger point is 0.4V for a logic-low level, and
1.8V for a logic-high level. The low 0.1µA (typ) shutdown
current is achieved by applying a voltage that is as near as
ground as possible to the SHUTDOWN pin. A voltage that is
higher than ground may increase the shutdown current.
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 100k. pull-up resistor between the
SHUTDOWN pin and VDD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier operation by opening the switch. Closing the switch connects the
SHUTDOWN pin to ground, activating micro-power shutdown.
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10
inches (millimeters) unless otherwise noted
Order Number LM4915LQ
NS Package Number LQB08A
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LM4915 Pseudo-Differential Mono Headphone Amplifier with Fixed 6dB Gain
Physical Dimensions
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