LM4867 Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function

LM4867

Output-Transient-Free Dual 2.1W Audio Amplifier Plus

No Coupling Capacitor Stereo Headphone Function

General Description

The LM4867 is a dual bridge-connected audio power ampli-

fier which, when connected to a 5V supply, will deliver 2.1W

to a 4

Ω

load (Note 1) or 2.4W to a 3

Ω

load (Note 2) with less

than 1.0% THD+N. The LM4867 uses advanced, latest gen-

eration circuitry to eliminate all traces of clicks and pops

when the supply voltage is first applied. The amplifier has a

headphone-amplifier-select input pin. It is used to switch the

amplifiers from bridge to single-ended mode for driving

headphones. A new circuit topology eliminates headphone

output coupling capacitors. A MUX control pin allows selec-

tion between the two sets of stereo input signals. The MUX

control can also be used to select between two different

customer-specified closed-loop responses.

Boomer audio power amplifiers are designed specifically to

provide high quality output power from a surface mount

package and require few external components. To simplify

audio system design, the LM4867 combines dual bridge

speaker amplifiers and stereo headphone amplifiers in one

package.

The LM4867 features an externally controlled power-saving

micropower shutdown mode, a stereo headphone amplifier

mode, and thermal shutdown protection.

Note 1: An LM4867LQ or LM4867MTE that has been properly mounted to

a circuit board will deliver 2.1W into 4

Ω

. The Mux control can also be used to

select two different closed-loop responses. LM4867MT will deliver 1.1W into

Ω

. See the Application Information sections for further information concern-

ing the LM4867LQ and the LM4867MT.

Note 2: An LM4867LQ or LM4867MTE that has been properly mounted to a

circuit board and forced-air cooled will deliver 2.4W into 3

Ω

Key Specifications

at 1% THD+N

LM4867LQ, 3

Ω

load

2.4W (typ)

LM4867LQ, 4

Ω

load

2.1W (typ)

LM4867MTE, 4

Ω

1.9W (typ)

LM4867MT, 8

Ω

1.1W (typ)

Single-ended mode - THD+N at 75mW into 32

Ω

0.5%

(max)

Shutdown current

0.7µA (typ)

Features

Advanced “click and pop” suppression circuitry

Eliminates headphone amplifier output coupling

capacitors

Stereo headphone amplifier mode

Input mux control and two separate inputs per channel

Thermal shutdown protection circuitry

LLP, TSSOP, and exposed-DAP TSSOP packaging

available

Applications

Multimedia monitors

Portable and desktop computers

Portable audio systems

Typical Application

Boomer

is a registered trademark of National Semiconductor Corporation.

DS200013-31

Refer to the Application Information section titled PROPER SELECTION OF EXTERNAL COMPONENTS for details concerning the value of C

FIGURE 1. Typical Audio Amplifier Application Circuit

(Pin out shown for the 24-pin Exposed-DAP LLP package. Numbers in ( ) are for the 20-pin MTE and MT

packages.)

February 2001

LM4867

Output-T

ransient-Free

Dual

2.1W

Audio

Amplifier

Plus

Coupling

Capacitor

Stereo

Headphone

Function

DS200013

www.national.com

Absolute Maximum Ratings

(Note 3)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage

6.0V

Storage Temperature

−65˚C to +150˚C

Input Voltage

−0.3V to V

+0.3V

Power Dissipation (Note 4)

Internally limited

ESD Susceptibility (Note 5)

All pins except Pin 3 (MT, MTE), Pin 2 (LQ)

2000V

Pin 3 (MT, MTE), Pin 2 (LQ)

8000V

ESD Susceptibility (Note 6)

200V

Junction Temperature

150˚C

Solder Information

Small Outline Package

Vapor Phase (60 sec.)

215˚C

Infrared (15 sec.)

220˚C

See AN-450 “Surface Mounting and their Effects on

Product Reliablilty” for other methods of soldering surface

mount devices.

Thermal Resistance

(typ) — MTC20

20˚C/W

(typ) — MTC20

80˚C/W

(typ) — MXA20A

2˚C/W

(typ) — MXA20A

41˚C/W (Note 7)

(typ) — MXA20A

51˚C/W (Note 8)

(typ) — MXA20A

90˚C/W (Note 9)

(typ) — LQA24A

3.0˚C/W

(typ) — LQA24A

TBD˚C/W (Note 10)

(typ) — LQA24A

TBD˚C/W (Note 11)

(typ) — LQA24A

TBD˚C/W (Note 12)

Operating Ratings

Temperature Range

MIN

≤

MAX

−40˚C

≤

85˚C

Supply Voltage

2.0V

≤

5.5V

Electrical Characteristics for Entire IC

(Notes 3, 13)

The following specifications apply for V

= 5V unless otherwise noted. Limits apply for T

= 25˚C.

Symbol

Parameter

Conditions

LM4867

Units

(Limits)

Typical

Limit

(Note 14)

(Note 15)

Supply Voltage

V (min)

5.5

V (max)

Quiescent Power Supply Current

= 0V, I

= 0A (Note 16) , HP-IN = 0V

7.5

mA (max)

= 0V, I

= 0A (Note 16) , HP-IN = 4V

3.0

mA (max)

Shutdown Current

applied to the SHUTDOWN pin

0.7

µA (max)

Electrical Characteristics for Bridged-Mode Operation

(Notes 3, 13)

The following specifications apply for V

= 5V unless otherwise specified. Limits apply for T

= 25˚C.

Symbol

Parameter

Conditions

LM4867

Units

(Limits)

Typical

Limit

(Note 14)

(Note 15)

Output Offset Voltage

= 0V

mV (max)

Output Power (Note 17)

THD = 1%, f = 1kHz

LM4867MTE, R

= 3

Ω

(Note 18)

2.2

LM4867LQ, R

= 3

Ω

(Note 18)

2.2

LM4867MTE, R

= 4

Ω

(Note 19)

1.9

LM4867LQ, R

= 4

Ω

(Note 19)

1.9

LM4867, R

= 8

Ω

1.1

1.0

W (min)

THD+N = 10%, f = 1kHz

LM4867MTE, R

= 3

Ω

(Note 18)

3.0

LM4867LQ, R

= 3

Ω

(Note 18)

3.0

LM4867MTE, R

= 4

Ω

(Note 19)

2.6

LM4867LQ, R

= 4

Ω

(Note 19)

2.6

LM4867, R

= 8

Ω

1.5

THD+N = 1%, f = 1 kHz, R

= 32

Ω

0.34

LM4867

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Electrical Characteristics for Bridged-Mode Operation

(Notes 3, 13) (Continued)

The following specifications apply for V

= 5V unless otherwise specified. Limits apply for T

= 25˚C.

Symbol

Parameter

Conditions

LM4867

Units

(Limits)

Typical

Limit

(Note 14)

(Note 15)

THD+N

Total Harmonic Distortion+Noise

20Hz

≤

20kHz, A

= 2

LM4867MTE, R

= 4

Ω

, P

= 2W

LM4867LQ, R

= 4

Ω

, P

= 2W

LM4867, R

= 8

Ω

, P

= 1W

0.3

PSRR

Power Supply Rejection Ratio

= 5V, V

RIPPLE

= 200 mV

RMS

, R

= 8

Ω

= 2.2µF

TALK

Channel Separation

f = 1 kHz, C

= 2.2µF

SNR

Signal To Noise Ratio

= 5V, P

= 1.1W, R

= 8

Ω

Electrical Characteristics for Single-Ended Operation

(Notes 3, 13)

The following specifications apply for V

= 5V unless otherwise specified. Limits apply for T

= 25˚C.

Symbol

Parameter

Conditions

LM4867

Units

(Limits)

Typical

Limit

(Note 14)

(Note 15)

Output Offset Voltage

= 0V

mV (max)

Output Power

THD = 0.5%, f = 1kHz, R

= 32

Ω

mW (min)

THD+N = 1%, f = 1kHz, R

= 8

Ω

(Note

20)

180

THD+N = 1%, f = 1kHz, R

= 16

Ω

THD+N = 10%, f = 1kHz, R

= 32

Ω

THD+N = 10%, f = 1kHz, R

= 16

Ω

THD+N = 10%, f = 1kHz, R

= 32

Ω

165

208

114

OUT

Output Voltage Swing

THD = 0.05%, R

= 5k

Ω

P-P

THD+N

Total Harmonic Distortion+Noise

= −1, P

= 75mW, 20 Hz

≤

20kHz,

= 32

Ω

0.2

PSRR

Power Supply Rejection Ratio

= 2.2µF, V

RIPPLE

= 200mV

RMS

f = 1kHz

TALK

Channel Separation

f = 1kHz, C

= 2.2µF

SNR

Signal To Noise Ratio

= 5V, P

= 340mW, R

= 8

Ω

Note 3: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which

guarantee specific performance limits. This assumes that the device operates within the Operating Ratings. Specifications are not guaranteed for parameters where

no limit is given. The typical value however, is a good indication of device performance.

Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by T

JMAX

, and the ambient temperature T

. The maximum

allowable power dissipation is P

DMAX

= (T

JMAX

− T

. For the LM4867, T

JMAX

= 150˚C. For the

s for different packages, please see the Application

Information section or the Absolute Maximum Ratings section.

Note 5: Human body model, 100 pF discharged through a 1.5 k

Ω

resistor.

Note 6: Machine model, 220 pF–240 pF discharged through all pins.

Note 7: The given

is for an LM4867 packaged in an MXA20A with the Exposed-DAP soldered to an exposed 2in

area of 1oz printed circuit board copper.

Note 8: The given

is for an LM4867 packaged in an MXA20A with the Exposed-DAP soldered to an exposed 1in

area of 1oz printed circuit board copper.

Note 9: The given

is for an LM4867 packaged in an MXA20A with the Exposed-DAP not soldered to printed circuit board copper.

Note 10: The given

is for an LM4867 packaged in an LQA24A with the Exposed-DAP soldered to an exposed 2in

area of 1oz printed circuit board copper.

Note 11: The given

is for an LM4867 packaged in an LQA24A with the Exposed-DAP soldered to an exposed 1in

area of 1oz printed circuit board copper.

Note 12: The given

is for an LM4867 packaged in an LQA24A with the Exposed-DAP not soldered to printed circuit board copper.

Note 13: All voltages are measured with respect to the ground (GND) pins, unless otherwise specified.

Note 14: Typicals are measured at 25˚C and represent the parametric norm.

Note 15: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are guaranteed by design, test, or

statistical analysis.

Note 16: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.

Note 17: Output power is measured at the device terminals.

Note 18: When driving 3

Ω

loads from a 5V supply, the LM4867LQ, LM4867MTE, or LM4867MTE-1 must be mounted to the circuit board and forced-air cooled (450

linear-feet per minute).

Note 19: When driving 4

Ω

loads from a 5V supply, the LM4867LQ, LM4867MTE or LM4867MTE-1 must be mounted to the circuit board.

LM4867

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Electrical Characteristics for Single-Ended Operation

(Notes 3, 13) (Continued)

Note 20: See Application Information section ’Single-Ended Output Power Performance and Measurement Considerations’ for more information.

Typical Performance Characteristics

MTE- and LQ- Specific Characteristics

Note 21: This curve shows the LM4867MTE’s thermal dissipation ability at different ambient temperatures given these conditions:

500LFPM + JEDEC board: The part is soldered to a 1S2P 20-lead exposed-DAP TSSOP test board with 500 linear feet per minute of forced-air flow across

it.

Board information - copper dimensions: 74x74mm, copper coverage: 100% (buried layer) and 12% (top/bottom layers), 16 vias under the exposed-DAP.

500LFPM + 2.5in

: The part is soldered to a 2.5in

, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it.

2.5in

: The part is soldered to a 2.5in

, 1oz. copper plane.

Not Attached: The part is not soldered down and is not forced-air cooled.

LM4867MTE

THD+N vs Output Power

DS200013-33

LM4867MTE

THD+N vs Frequency

DS200013-34

LM4867LQ

THD+N vs Output Power

DS200013-53

LM4867LQ

THD+N vs Frequency

DS200013-54

LM4867MTE

THD+N vs Output Power

DS200013-36

LM4867LQ

THD+N vs Output Power

DS200013-55

LM4867LQ, LM4867MTE

Power Dissipation vs Power Output

DS200013-61

LM4867LQ, LM4867MTE(Note 21)

Power Derating Curve

DS200013-59

LM4867

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External Components Description

( Refer to Figure 1. )

Components

Functional Description

Inverting input resistance which sets the closed-loop gain in conjunction with R

. This resistor also forms a

high pass filter with C

at f

= 1/(2

Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a

highpass filter with R

at f

= 1/(2

). Refer to the section, Proper Selection of External Components,

for an explanation of how to determine the value of C

Feedback resistance which sets the closed-loop gain in conjunction with R

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.

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 C

Application Information

ELIMINATING OUTPUT COUPLING CAPACITORS

Typical single-supply audio amplifiers that can switch be-

tween

driving

bridge-tied-load

(BTL)

speakers

and

single-ended (SE) headphones use a coupling capacitor on

each SE output. This capacitor blocks the half-supply volt-

age to which the output amplifiers are typically biased and

couples the audio signal to the headphones. The signal

return to circuit ground is through the headphone jack’s

sleeve.

The LM4867 eliminates these coupling capacitors. Amp2A is

internally configured to apply V

/2 to a stereo headphone

jack’s sleeve. This voltage matches the quiescent voltage

present on the Amp1A and Amp1B outputs that drive the

headphones. The headphones operate in a manner very

similar to a bridge-tied-load (BTL). The same DC voltage is

applied to both headphone speaker terminals. This results in

no net DC current flow through the speaker. AC current flows

through a headphone speaker as an audio signal’s output

amplitude increases on the speaker’s terminal.

When operating as a headphone amplifier, the headphone

jack sleeve is not connected to circuit ground. Using the

headphone output jack as a line-level output will place the

LM4867’s one-half supply voltage on a plug’s sleeve con-

nection.

Driving

portable

notebook

computer

audio-visual display equipment is possible. This presents no

difficulty when the external equipment uses capacitively

coupled inputs. For the very small minority of equipment that

is DC-coupled, the LM4867 monitors the current supplied by

the amplifier that drives the headphone jack’s sleeve. If this

current exceeds 500mA

, the amplifier is shutdown, pro-

tecting the LM4867 and the external equipment. For more

information, see the section titled ’Single-Ended Output

Power Performance and Measurement Considerations’.

OUTPUT TRANSIENT (’POPS AND CLICKS’)

ELIMINATED

The LM4867 contains advanced circuitry that eliminates out-

put transients (’pop and click’). This circuitry prevents all

traces of transients when the supply voltage is first applied,

when the part resumes operation after shutdown, or when

switching between BTL speakers and SE headphones. Two

circuits combine to eliminate pop and click. One circuit

mutes the output when switching between speaker loads.

Another circuit monitors the input signal. It maintains the

muted condition until there is sufficient input signal magni-

tude to mask any remaining transient that may occur.

Figure 2 shows the LM4867’s lack of transients in the differ-

ential signal (Trace B) across a BTL 8

Ω

load. The LM4867’s

active-high SHUTDOWN pin is driven by the logic signal

shown in Trace A. Trace C is the VOUT- output signal and

trace D is the VOUT+ output signal. The shutdown signal

frequency is 1Hz with a 50% duty cycle.

Figure 3 is gener-

ated with the same conditions except that the output drives a

Ω

single-ended (SE) load. Again, no trace of output tran-

sients is seen.

USING THE LM4867 TO UPGRADE LM4863 AND LM4873

DESIGNS

The

LM4867’s

noise-free

operation

plus

coupling-capacitorless headphone operation and functional

compatibility with the LM4873 and the LM4863 simplifies

upgrading systems using these parts. Upgrading older de-

signs that use either the LM4863 or the LM4873 is easy.

Simply remove and short the coupling capacitors located

between the LM4873’s or LM4863’s Amp1A and Amp1B

outputs and the headphone connections. Also remove the

Ω

resistor between each headphone connection and

ground. Finally, remove any resistors connected to the

HP-IN pin (typically two 100k

Ω

resistors). Connect the HP-IN

pin directly to the headphone jack control pin as shown in

Figure 4.

DS200013-56

FIGURE 2. Differential output signal (Trace B) is devoid

of transients. The SHUTDOWN pin is driven by a

shutdown signal (Trace A). The inverting output (Trace

C) and the non-inverting output (Trace D) are applied

across an 8

Ω

BTL load.

LM4867

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Application Information

(Continued)

The LM4867’s pin configuration simplifies the process of

upgrading systems that use the LM4863. Except for its four

MUX function pins, the LM4867’s pin configuration matches

the LM4863’s pin configuration. If the LM4867’s MUX func-

tionality is not needed when replacing an LM4863, connect

the MUX CTRL pin to either V

or ground. To ensure

correct amplifier operation, unused MUX inputs must be

tied to GND. As shown in Table 1, grounding the MUX CTRL

pin selects stereo input 1 (−IN A1 and −IN B1), whereas

applying V

to the MUX CTRL pin selects stereo input 2

(−IN A2 and −IN B2).

The LM4867’s unique headphone sense circuit requires a

dual switch headphone jack. Replace the four-terminal head-

phone jack used with the LM4863 and LM4873 with the

five-terminal headphone jack, such as the Switchcraft

35RAPC4BH3, shown in Figure 4. Connect the +OUT A

(Amp2A) pin to the five-terminal headphone jack’s sleeve

pin.

DS200013-57

FIGURE 3. Single-ended output signal (Trace B) is

devoid of transients. The SHUTDOWN pin is driven by

a shutdown signal (Trace A). The inverting output

(Trace C) and the V

BYPASS

output (Trace D) are applied

across a 32

Ω

BTL load.

DS200013-31

FIGURE 4. Typical Audio Amplifier Application Circuit

(Pin out shown for the 24-pin Exposed-DAP LLP package. Numbers in ( ) are for the 20-pin MTE and MT packages.)

LM4867

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Application Information

(Continued)

STEREO-INPUT MULTIPLEXER (STEREO MUX)

The LM4867 has two stereo inputs. The MUX CTRL Pin

controls which stereo input is active. As shown in the Truth

Table for Logic Inputs, applying 0V to the MUX CTRL input

activates stereo input 1, whereas applying V

to the MUX

CTRL inputs activates stereo input 2. To ensure correct

amplifier operation, unused MUX inputs must be tied to

GND.

Typical LM4867 applications use the MUX to switch between

two stereo input signals. Each stereo channel’s gain can be

tailored to produce the required output signal level by choos-

ing the appropriate input and feedback resistor ratio.

Another configuration uses the MUX to select two different

gains or frequency compensated gains that amplify a single

pair of stereo input signals.

Figure 5 shows two different

feedback networks, Network 1 and Network 2. Network 1

produces increasing gain as the input signal’s frequency

decreases. This can be used to compensate a small,

full-range speaker’s low frequency response roll-off. Network

2 sets the gain for an alternate load such as headphones.

The circuit in

Figure 6 uses Network 1 when driving external

speakers, switching to Network 2 when headphones are

connected. The normally closed control switch in

Figure 6’s

headphone jack connects to the MUX CTRL pin. When

headphones are connected, the LM4867’s internal pull-up

that applies V

to the HP-IN and the external 100k

Ω

resis-

tor applies V

to MUX CTRL pin. Simultaneously applying

these control voltages automatically selects the amplifier

(headphone or bridge) and switches the gain (MUX channel

selection). Alternatively, leaving the MUX CTRL pin indepen-

dently accessible allows a user to select bass boost as

needed. This alternative user-selectable bass-boost scheme

requires connecting equal ratio resistor feedback networks

to each MUX input channel. The value of the resistor in the

RC network is chosen to give a gain that is necessary to

achieve the desired bass-boost.

Switching between the MUX channels may change the input

signal source or the feedback resistor network. During the

channel switching transition, the average voltage level

present on the internal amplifier’s input may change. This

change can slew at a rate that may produce audible voltage

transients or clicks in the amplifier’s output signal. Using the

MUX to select between two vastly dissimilar gains is a typical

transient-producing situation. As the MUX is switched, an

audible click may occur as the gain suddenly changes.

PIN OUT COMPATIBILITY WITH THE LM4863

The LM4867 pin out was designed to simplify replacing the

LM4863: except for the four Pins(-IN A

, MUX CTRL, -IN B

and NC) that implement the LM4867’s extra functionality, the

LM4867MT/MTE and LM4863MT/MTE pin outs match.

(Note 22)

Note 22: If the LM4867 replaces an LM4863 and the input MUX circuitry is

not being used, the LM4867 MUX CTRL pin must be tied to V

or GND and

the unused MUX inputs must be connected to GND.

EXPOSED-DAP MOUNTING CONSIDERATIONS

The LM4867’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 surround-

ing PCB