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PDF LM4995 Data sheet ( Hoja de datos )
| Número de pieza | LM4995 | |
| Descripción | 1.3W Audio Power Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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September 2007
LM4995
1.3 W Audio Power Amplifier
General Description
The LM4995 is an audio power amplifier primarily designed
for demanding applications in mobile phones and other
portable communication device applications. It is capable of
delivering 1.2W of continuous average power to an 8Ω BTL
load with less than 1% distortion (THD+N) from a 5VDC power
supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
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The LM4995 does not require output
bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage appli-
cations where minimal power consumption is a primary re-
quirement.
The LM4995 features a low-power consumption shutdown
mode, which is achieved by driving the shutdown pin with
logic low. Additionally, the LM4995 features an internal ther-
mal shutdown protection mechanism.
The LM4995 contains advanced pop & click circuitry which
eliminates noise which would otherwise occur during turn-on
and turn-off transitions.
The LM4995 is unity-gain stable and can be configured by
external gain-setting resistors.
Key Specifications
■ PSRR at 3.6V (217Hz & 1kHz)
■
Output Power at 5.0V, 1% THD+N, 8Ω
■
Output Power at 3.6V, 1% THD+N, 8Ω
■ Shutdown Current
75dB
1.3W (typ)
625mW (typ)
0.01µA (typ)
Features
■ Available in space-saving 0.4mm pitch μSMD package
■ Ultra low current shutdown mode
■ BTL output can drive capacitive loads
■ Improved pop & click circuitry eliminates noise during turn-
on and turn-off transitions
■ 2.4 - 5.5V operation
■ No output coupling capacitors, snubber networks or
bootstrap capacitors required
■ Unity-gain stable
■ External gain configuration capability
■ LLP package: 0.5mm pitch, 3 x 3 mm
Applications
■ Mobile Phones
■ PDAs
■ Portable electronic devices
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2007 National Semiconductor Corporation 201599
www.national.com
1 page  
TEhleefoclltorwiincgaslpeCcifhicaatiroanscatpeplryifsorttihcescirVcuDit Dsho=wn3in.0FVigure(N1,outensle1s,s2o)therwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4995
Typical
Limit
(Note 6)
(Notes 7, 8)
Units
(Limits)
IDD
ISD
VOS
Po
TWU
THD+N
PSRR
Quiescent Power Supply Current
Shutdown Current
Output Offset Voltage
Output Power
Wake-up time
Total Harmonic Distortion + Noise
Power Supply Rejection Ratio
VIN = 0V, Io = 0A, No Load
VIN = 0V, Io = 0A, 8Ω Load
VSD = VGND
No Load
THD+N = 1% (max); f = 1 kHz
Po = 250mWRMS; f = 1kHz
Vripple = 200mV sine p-p
Input terminated to GND
1.3
1.6
0.01
5
400
110
0.07
74 (f = 217Hz)
75 (f = 1kHz)
mA
mA
µA
mV
mW
ms
%
dB
VSDIH
Shutdown Voltage Input High
VwSwDIwL .DataSShheuetdt4oUw.ncoVmoltage Input Low
1.2 V
1V
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions
which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters
where no limit is given, however, the typical value is a good indication of device performance.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature TA. The maximum
allowable power dissipation is PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4995, see power derating
curves for additional 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 specification limits are guaranteed by design, test, or statistical analysis.
Note 9: ROUT is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the two 20kΩ resistors.
Note 10: If the product is in Shutdown mode and VDD exceeds 6V (to a max of 8V VDD), then most of the excess current will flow through the ESD protection
circuits. If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is enabled when VDD is greater than 5.5V
and less than 6.5V, no damage will occur, although operation life will be reduced. Operation above 6.5V with no current limit will result in permanent damage.
Note 11: Maximum power dissipation in the device (PDMAX) occurs at an output power level significantly below full output power. PDMAX can be calculated using
Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs.
External Components Description
(Figure 1)
Components
Functional Description
1. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high
pass filter with Ci at fC= 1/(2π RiCi).
2. Ci Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a highpass filter
with Ri at fC = 1/(2π RiCi). Refer to the section, Proper Selection of External Components, for an explanation of
how to determine the value of Ci.
3. Rf Feedback resistance which sets the closed-loop gain in conjunction with Ri.
4. CS Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for
information concerning proper placement and selection of the supply bypass capacitor.
5. CB Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External
Components, for information concerning proper placement and selection of CB.
5 www.national.com
5 Page 
width is dictated by the choice of external components shown
in Figure 1. The input coupling capacitor, Ci, forms a first order
high pass filter which limits low frequency response. This val-
ue should be chosen based on needed frequency response
for a few distinct reasons.
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 attenua-
tion. But in many cases the speakers used in portable sys-
tems, 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 effected 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
wwsizwe.DbaatsaeSdheoent4nUe.cceosmsary low frequency response, turn-on
pops can be minimized.
Besides minimizing the input capacitor size, careful consid-
eration 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 LM4995 turns on.
The slower the LM4995'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), should produce a virtually
clickless and popless shutdown function. While the device will
function properly, (no oscillations or motorboating), with CB
equal to 0.1µF, the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CB equal to 1.0µF is
recommended in all but the most cost sensitive designs.
AUDIO POWER AMPLIFIER DESIGN
A 1W/8Ω Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
1 Wrms
8Ω
1 Vrms
20 kΩ
100 Hz–20 kHz ± 0.25 dB
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics section, the supply rail can be
easily found.
5V is a standard voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4995 to reproduce peaks in excess of 1W with-
out producing audible distortion. At this time, the designer
must make sure that the power supply choice along with the
output impedance does not violate the conditions explained
in the Power Dissipation section.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 2.
Rf/Ri = AVD/2
(2)
From Equation 2, the minimum AVD is 2.83; use AVD = 3.
Since the desired input impedance was 20 kΩ, and with a
AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results in an
allocation of Ri = 20 kΩ and Rf = 30 kΩ. The final design step
is to address the bandwidth requirements which must be stat-
ed as a pair of −3 dB frequency points. Five times away from
a −3 dB point is 0.17 dB down from passband response which
is better than the required ±0.25 dB specified.
fL = 100Hz/5 = 20Hz
fH = 20kHz * 5 = 100kHz
As stated in the External Components section, Ri in con-
junction with Ci create a highpass filter.
Ci ≥ 1/(2π*20 kΩ*20 Hz) = 0.397 µF; use 0.39 µF
The high frequency pole is determined by the product of the
desired frequency pole, fH, and the differential gain, AVD. With
a AVD = 3 and fH = 100kHz, the resulting GBWP = 300kHz
which is much smaller than the LM4995 GBWP of 2.5MHz.
This figure displays that if a designer has a need to design an
amplifier with a higher differential gain, the LM4995 can still
be used without running into bandwidth limitations.
The LM4995 is unity-gain stable and requires no external
components besides gain-setting resistors, an input coupling
capacitor, and proper supply bypassing in the typical appli-
cation. However, if a closed-loop differential gain of greater
than 10 is required, a feedback capacitor (C4) may be needed
as shown in Figure 2 to bandwidth limit the amplifier. This
feedback capacitor creates a low pass filter that eliminates
possible high frequency oscillations. Care should be taken
when calculating the -3dB frequency in that an incorrect com-
bination of R3 and C4 will cause rolloff before 20kHz. A typical
combination of feedback resistor and capacitor that will not
produce audio band high frequency rolloff is R3 = 20kΩ and
C4 = 25pf. These components result in a -3dB point of ap-
proximately 320kHz.
11 www.national.com
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| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LM4995.PDF ] | |
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