LM4995TMBD - National Semiconductor

LM4995 November 19, 2009

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

external components. The LM4995 does not require output

coupling capacitors or 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) 75dB

■ Output Power at 5.0V, 1% THD+N, 8Ω1.3W (typ)

■ Output Power at 3.6V, 1% THD+N, 8Ω625mW (typ)

■ Shutdown Current 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

Typical Application

201599d3

FIGURE 1. Typical Audio Amplifier Application Circuit

Boomer® is a registered trademark of National Semiconductor Corporation.

LM4995 1.3 W Audio Power Amplifier

Connection Diagrams

TM Package

20159903

Top View

Order Number LM4995TM

See NS Package Number TMD09AAA

TM Marking

20159949

Top View

X - Date Code

V - Die Traceability

G - Boomer Family

G8 - LM4995TM

SD Package

20159957

Top View

Order Number LM4995SD

See NS Package Number SDA08A

SD Marking

20159999

Top View

Z - Assembly Plant code

XY - 2 Digit date code

TT - Die Traceability

L4995 - LM4995SD

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LM4995

Absolute Maximum Ratings (Note 2)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage (Note 10) 6.0V

Storage Temperature −65°C to +150°C

Input Voltage −0.3V to VDD +0.3V

Power Dissipation (Note 3, Note

11)Internally Limited

ESD Susceptibility (Note 4) 2000V

ESD Susceptibility (Note 5) 200V

Junction Temperature 150°C

Thermal Resistance

θJA (TM) 96.5°C/W

θJA (SD) 56°C/W

Operating Ratings

Temperature Range

TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ 85°C

Supply Voltage 2.4V ≤ VDD ≤ 5.5V

Electrical Characteristics VDD = 5V (Note 1, Note 2)

The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM4995

Units

(Limits)

Typical Limit

(Note 6) (Note 7, Note

IDD Quiescent Power Supply Current VIN = 0V, Io = 0A, No Load 1.5 2.5 mA (max)

VIN = 0V, Io = 0A, 8Ω Load 1.8 mA

ISD Shutdown Current VSD = VGND 0.01 1 µA (max)

VOS Output Offset Voltage No Load 5 26 mV (max)

PoOutput Power THD+N = 1% (max); f = 1 kHz 1.3 (TM)

1.25 (SD)

TWU Wake-up time 165 ms

THD+N Total Harmonic Distortion + Noise Po = 500mWRMS; f = 1kHz 0.08 %

PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p

Input terminated to GND

73 (f = 217Hz)

73 (f = 1kHz) dB

VSDIH Shutdown Voltage Input High 1.5 V

VSDIL Shutdown Voltage Input Low 1.2 V

Electrical Characteristics VDD = 3.6V (Note 1, Note 2)

The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM4995

Units

(Limits)

Typical Limit

(Note 6) (Note 7, Note

IDD Quiescent Power Supply Current VIN = 0V, Io = 0A, No Load 1.3 2.3 mA (max)

VIN = 0V, Io = 0A, 8Ω Load 1.6 mA

ISD Shutdown Current VSD = VGND 0.01 1 µA (max)

VOS Output Offset Voltage No Load 5 26 mV (max)

Output Power THD+N = 1% (max); f = 1 kHz 625 (TM)

610 (SD)

TWU Wake-up time 130 ms

THD+N Total Harmonic Distortion + Noise Po = 300mWRMS; f = 1kHz 0.07 %

PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p

Input terminated to GND

75 (f = 217Hz)

76 (f = 1kHz) dB

VSDIH Shutdown Voltage Input High 1.3 V

VSDIL Shutdown Voltage Input Low 1 V

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LM4995

Electrical Characteristics VDD = 3.0V (Note 1, Note 2)

The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM4995

Units

(Limits)

Typical Limit

(Note 6) (Note 7, Note

IDD Quiescent Power Supply Current VIN = 0V, Io = 0A, No Load 1.3 mA

VIN = 0V, Io = 0A, 8Ω Load 1.6 mA

ISD Shutdown Current VSD = VGND 0.01 µA

VOS Output Offset Voltage No Load 5 mV

PoOutput Power THD+N = 1% (max); f = 1 kHz 400 mW

TWU Wake-up time 110 ms

THD+N Total Harmonic Distortion + Noise Po = 250mWRMS; f = 1kHz 0.07 %

PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p

Input terminated to GND

74 (f = 217Hz)

75 (f = 1kHz) dB

VSDIH Shutdown Voltage Input High 1.2 V

VSDIL Shutdown Voltage Input Low 1 V

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. RiInverting 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. CiInput 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. RfFeedback resistance which sets the closed-loop gain in conjunction with Ri.

4. CSSupply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for

information concerning proper placement and selection of the supply bypass capacitor.

5. CBBypass 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.

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LM4995

Typical Performance Characteristics

THD+N vs Output Power

VDD = 3V, RL = 8Ω

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THD+N vs Output Power

VDD = 3.6V, RL = 8Ω

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THD+N vs Output Power

VDD = 5V, RL = 8Ω

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THD+N vs Frequency

VDD = 3V, RL = 8Ω,

f = 1kHz, PO = 250mW

20159942

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LM4995

THD+N vs Frequency

VDD = 3.6V, RL = 8Ω,

f = 1kHz, PO = 300mW

20159941

THD+N vs Frequency

VDD = 5V, RL = 8Ω,

f = 1kHz, PO = 500mW

20159943

PSRR vs Frequency

VDD = 3V, RL = 8Ω

20159950

PSRR vs Frequency

VDD = 3.6V, RL = 8Ω

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LM4995

PSRR vs Frequency

VDD = 5V, RL = 8Ω

20159951

Power Dissipation vs Output Power

VDD = 3V, RL = 8Ω

20159909

Power Dissipation vs Output Power

VDD = 3.6V, RL = 8Ω

20159908

Power Dissipation vs Output Power

VDD = 5V, RL = 8Ω

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LM4995

Output Level vs Frequency Response

(Three different caps)

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Shutdown Voltage VSDIH

VDD = 3V

20159936

Shutdown Voltage VSDIH

VDD = 3.6V

20159947

Shutdown Voltage VSDIH

VDD = 5V

20159937

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LM4995

Shutdown Voltage VSDIL

VDD = 3V

20159939

Shutdown Voltage VSDIL

VDD = 3.6V

20159948

Shutdown Voltage VSDIL

VDD = 5V

20159940

Output Power vs Supply Voltage

RL = 8Ω

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LM4995

Application Information

BRIDGE CONFIGURATION EXPLANATION

As shown in Figure 1, the LM4995 has two internal opera-

tional amplifiers. The first amplifier's gain is externally config-

urable, while the second amplifier is internally fixed in a unity-

gain, inverting configuration. The closed-loop gain of the first

amplifier is set by selecting the ratio of Rf to Ri while the sec-

ond amplifier's gain is fixed by the two internal 20kΩ resistors.

Figure 1 shows that the output of amplifier one serves as the

input to amplifier two which results in both amplifiers produc-

ing signals identical in magnitude, but out of phase by 180°.

Consequently, the differential gain for the IC is

AVD= 2 *(Rf/Ri)

By driving the load differentially through outputs Vo1 and Vo2,

an amplifier configuration commonly referred to as “bridged

mode” is established. Bridged mode operation is different

from the classical single-ended amplifier configuration where

one side of the load is connected to ground.

A bridge amplifier design has a few distinct advantages over

the single-ended configuration, as it provides differential drive

to the load, thus doubling output swing for a specified supply

voltage. Four times the output power is possible as compared

to a single-ended amplifier under the same conditions. This

increase in attainable output power assumes that the ampli-

fier is not current limited or clipped. In order to choose an

amplifier's closed-loop gain without causing excessive clip-

ping, please refer to the Audio Power Amplifier Design

section.

A bridge configuration, such as the one used in LM4995, 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. This elimi-

nates the need for an output coupling capacitor which is

required in a single supply, single-ended amplifier configura-

tion. Without an output coupling capacitor, the half-supply

bias across the load would result in both increased internal IC

power dissipation and also possible loudspeaker damage.

POWER DISSIPATION

Power dissipation is a major concern when designing a suc-

cessful amplifier, whether the amplifier is bridged or single-

ended. A direct consequence of the increased power

delivered to the load by a bridge amplifier is an increase in

internal power dissipation. Since the LM4995 has two opera-

tional amplifiers in one package, the maximum internal power

dissipation is 4 times that of a single-ended amplifier. The

maximum power dissipation for a given application can be

derived from the power dissipation graphs or from Equation

PDMAX = 4*(VDD)2/(2π2RL) (1)

It is critical that the maximum junction temperature TJMAX of

150°C is not exceeded. TJMAX can be determined from the

power derating curves by using PDMAX and the PC board foil

area. By adding copper foil, the thermal resistance of the ap-

plication can be reduced from the free air value of θJA, result-

ing in higher PDMAX values without thermal shutdown

protection circuitry being activated. Additional copper foil can

be added to any of the leads connected to the LM4995. It is

especially effective when connected to VDD, GND, and the

output pins. Refer to the application information on the

LM4995 reference design board for an example of good heat

sinking. If TJMAX still exceeds 150°C, then additional changes

must be made. These changes can include reduced supply

voltage, higher load impedance, or reduced ambient temper-

ature. Internal power dissipation is a function of output power.

Refer to the Typical Performance Characteristics curves

for power dissipation information for different output powers

and output loading.

POWER SUPPLY BYPASSING

As with any amplifier, proper supply bypassing is critical for

low noise performance and high supply rejection. The capac-

itor location on both the bypass and power supply pins should

be as close to the device as possible. A ceramic 0.1μF placed

in parallel with the tantalum 2.2μF bypass (CB) capacitor will

aid in supply stability. This does not eliminate the need for

bypassing the power supply pins of the LM4995. The selec-

tion of a bypass capacitor, especially CB, is dependent upon

PSRR requirements, click and pop performance (as ex-

plained in the section, Proper Selection of External Com-

ponents), system cost, and size constraints.

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the

LM4995 contains shutdown circuitry that is used to turn off the

amplifier's bias circuitry. This shutdown feature turns the am-

plifier off when logic low is placed on the shutdown pin. By

switching the shutdown pin to GND, the LM4995 supply cur-

rent draw will be minimized in idle mode. Idle current is

measured with the shutdown pin connected to GND. The trig-

ger point for shutdown is shown as a typical value in the

Shutdown Hysteresis Voltage graphs in the Typical Perfor-

mance Characteristics section. It is best to switch between

ground and supply for maximum performance. While the de-

vice may be disabled with shutdown voltages in between

ground and supply, the idle current may be greater than the

typical value of 0.01µA. In either case, the shutdown pin

should be tied to a definite voltage to avoid unwanted state

changes.

In many applications, a microcontroller or microprocessor

output is used to control the shutdown circuitry, which pro-

vides a quick, smooth transition to shutdown. Another solution

is to use a single-throw switch in conjunction with an external

pull-up resistor. This scheme guarantees that the shutdown

pin will not float, thus preventing unwanted state changes.

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 LM4995 is tolerant of external

component combinations, consideration to component values

must be used to maximize overall system quality.

The LM4995 is unity-gain stable which gives the designer

maximum system flexibility. The LM4995 should be used in

low gain configurations to minimize THD+N values, and max-

imize the signal to noise ratio. Low gain configurations require

large input signals to obtain a given output power. Input sig-

nals equal to or greater than 1 Vrms are available from

sources such as audio codecs. Please refer to the section,

Audio Power Amplifier Design, for a more complete expla-

nation of proper gain selection.

Besides gain, one of the major considerations is the closed-

loop bandwidth of the amplifier. To a large extent, the band-

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LM4995

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

size based on necessary 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 1 Wrms

Load Impedance 8Ω

Input Level 1 Vrms

Input Impedance 20 kΩ

Bandwidth 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.

(2)

Rf/Ri = AVD/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.

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LM4995

201599d4

FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER

201599d5

FIGURE 3. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4995

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LM4995

201599d6

FIGURE 4. REFERENCE DESIGN BOARD SCHEMATIC

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LM4995

PCB LAYOUT GUIDELINES

This section provides practical guidelines for mixed signal

PCB layout that involves various digital/analog power and

ground traces. Designers should note that these are only

"rule-of-thumb" recommendations and the actual results will

depend heavily on the final layout.

GENERAL MIXED SIGNAL LAYOUT RECOMMENDATION

Power and Ground Circuits

For 2 layer mixed signal design, it is important to isolate the

digital power and ground trace paths from the analog power

and ground trace paths. Star trace routing techniques (bring-

ing individual traces back to a central point rather than daisy

chaining traces together in a serial manner) can have a major

impact on low level signal performance. Star trace routing

refers to using individual traces to feed power and ground to

each circuit or even device. This technique will require a

greater amount of design time but will not increase the final

price of the board. The only extra parts required will be some

jumpers.

Single-Point Power / Ground Connections

The analog power traces should be connected to the digital

traces through a single point (link). A "Pi-filter" can be helpful

in minimizing High Frequency noise coupling between the

analog and digital sections. It is further recommended to put

digital and analog power traces over the corresponding digital

and analog ground traces to minimize noise coupling.

Placement of Digital and Analog Components

All digital components and high-speed digital signal traces

should be located as far away as possible from analog com-

ponents and circuit traces.

Avoiding Typical Design / Layout Problems

Avoid ground loops or running digital and analog traces par-

allel to each other (side-by-side) on the same PCB layer.

When traces must cross over each other do it at 90 degrees.

Running digital and analog traces at 90 degrees to each other

from the top to the bottom side as much as possible will min-

imize capacitive noise coupling and cross talk.

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LM4995

Revision History

Rev Date Description

1.0 04/05/06 Initial WEB released of the datasheet.

1.1 05/17/06 Added the SD package.

1.2 08/07/06 Text edits.

1.3 08/22/06 Edited the THD+N Typical values on

the 3 EC tables, then re-released the D/

S to the WEB (per Allan S.).

1.4 09/11/07 Updated the SD pkg. diagram.

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LM4995

Physical Dimensions inches (millimeters) unless otherwise noted

TM Package

Order Number LM4995TM

NS Package Number TMD09AAA

X1 = 1.215± 0.03mm X2 = 1.215 ± 0.03mm X3 = 0.6 ± 0.075mm

SDPackage

Order Number LM4995SD

NS Package Number SDA08A

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LM4995

Notes

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LM4995

Notes

LM4995 1.3 W Audio Power Amplifier

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