National Semiconductor LM4908 Technical data

February 2004

LM4908
10kV ESD Rated, Dual 120 mW Headphone Amplifier

10kV ESD Rated, Dual 120 mW Headphone Amplifier

General Description

The LM4908 is a dual audio power amplifier capable of
delivering 120mW per channel of continuous average power
into a 16Ω load with 0.1% (THD+N) from a 5V power supply.

Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components using surface mount packaging. Since
the LM4908 does not require bootstrap capacitors or snub­ber networks, it is optimally suited for low-power portable
systems.

The unity-gain stable LM4908 can be configured by external
gain-setting resistors.

Key Specifications

j

THD+N at 1kHz at 120mW
continuous average output power
into 16Ω 0.1% (typ)

j

THD+N at 1kHz at 75mW
continuous average output power
into 32Ω 0.1% (typ)

Typical Application

j

Output power at 0.1% THD+N

at 1kHz into 32Ω 75mW (typ)

Features

n Up to 10kV ESD protection on all pins
n MSOP, SOP, and LLP surface mount packaging
n Switch on/off click suppression
n Excellent power supply ripple rejection
n Unity-gain stable
n Minimum external components

Applications

n Headphone Amplifier
n Personal Computers
n Portable electronic devices

*Refer to the Application Information Section for information concerning proper selection of the input and output coupling capacitors.

FIGURE 1. Typical Audio Amplifier Application Circuit

Boomer®is a registered trademark of National Semiconductor Corporation.

© 2004 National Semiconductor Corporation DS200752 www.national.com

20075201

Connection Diagrams

LM4908

SOP (MA) and MSOP (MM) Package

Top View

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Order Number LM4908MA, LM4908MM

See NS Package Number M08A, MUA08A

LLP (LQ) Package

Top View

Order Number LM4908LQ

See NS Package Number LQB08A

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LM4908

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

DD

+ 0.3V

θ

(MSOP) 56˚C/W

JC

θ

(MSOP) 210˚C/W

JA

θ

(SOP) 35˚C/W

JC

θ

(SOP) 170˚C/W

JA

θ

(LLP) 15˚C/W

JC

θ

(LLP) 117˚C/W (Note 9)

JA

θ

(LLP) 150˚C/W (Note 10)

JA

Power Dissipation (Note 4) Internally limited

ESD Susceptibility (Note 5) 10.0kV

Operating Ratings

ESD Susceptibility (Note 6) 500V

Junction Temperature 150˚C

Soldering Information (Note 1)

Small Outline Package

Vapor Phase (60 seconds) 215˚C

Infrared (15 seconds) 220˚C

Temperature Range

T

≤ TA≤ T

MIN

MAX

Supply Voltage 2.0V ≤ V

Note 1: See AN-450 “Surface Mounting and their Effects on Product Reli­ability” for other methods of soldering surface mount devices.

−40˚C ≤ TA≤ 85˚C

≤ 5.5V

DD

Thermal Resistance

Electrical Characteristics (Notes 2, 3)

The following specifications apply for VDD= 5V unless otherwise specified, limits apply to TA= 25˚C.

Symbol Parameter Conditions LM4908 Units

Typ

(Note 7)

V

DD

Supply Voltage 2.0 V (min)

Limit

(Note 8)

5.5 V (max)

I

DD

P

tot

V

OS

Supply Current VIN= 0V, IO= 0A 1.6 3.0 mA (max)

Total Power Dissipation VIN= 0V, IO= 0A 8 16.5 mW (max)

Input Offset Voltage VIN= 0V 5 50 mV (max)

Ibias Input Bias Current 10 pA

V

CM

G

V

Io Max Output Current THD+N

R

O

V

O

Common Mode Voltage

Open-Loop Voltage Gain RL=5kΩ 67 dB

<

0.1 % 70 mA

Output Resistance 0.1 Ω

Output Swing RL=32Ω, 0.1% THD+N, Min .3

R

=32Ω, 0.1% THD+N, Max 4.7

L

PSRR Power Supply Rejection Ratio Cb = 1.0µF, Vripple = 100mV

,

PP

0V

4.3 V

90 dB

f = 40Hz

Crosstalk Channel Separation RL=32Ω, f = 1kHz 82 dB

THD+N Total Harmonic Distortion + Noise f=1kHz

SNR Signal-to-Noise Ratio V

f

G

P

o

Unity Gain Frequency Open Loop, RL=5kΩ 25 MHz

Output Power THD+N = 0.1%,f=1kHz

R

=16Ω,

L

=3.5VPP(at 0 dB)

V

O

R

=32Ω,

L

=3.5VPP(at 0 dB)

V

O

= 3.5Vpp(at 0 dB) 100 dB

O

R

=16Ω 120 mW

L

R

=32Ω 75 60 mW

L

0.05 %

66 dB

0.05 %

66 dB

THD+N = 10%,f=1kHz

R

=16Ω 157 mW

L

R

=32Ω 99 mW

L

C

I

Input Capacitance 3 pF

(Limits)

V

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Electrical Characteristics (Notes 2, 3) (Continued)

The following specifications apply for VDD= 5V unless otherwise specified, limits apply to TA= 25˚C.

LM4908

Symbol Parameter Conditions LM4908 Units

Typ

(Note 7)

C

L

Load Capacitance 200 pF

Limit

(Note 8)

SR Slew Rate Unity Gain Inverting 3 V/µs

Electrical Characteristics (Notes 2, 3)

The following specifications apply for VDD= 3.3V unless otherwise specified, limits apply to TA= 25˚C.

Symbol Parameter Conditions Conditions Units

Typ

(Note 7)

I

DD

V

OS

P

o

Supply Current VIN= 0V, IO= 0A 1.4 mA (max)

Input Offset Voltage VIN= 0V 5 mV (max)

Output Power THD+N = 0.1%,f=1kHz

R

=16Ω 43 mW

L

R

=32Ω 30 mW

L

THD+N = 10%,f=1kHz

R

=16Ω 61 mW

L

R

=32Ω 41 mW

L

Limit

(Note 8)

(Limits)

(Limits)

Electrical Characteristics (Notes 2, 3)

The following specifications apply for VDD= 2.6V unless otherwise specified, limits apply to TA= 25˚C.

Symbol Parameter Conditions Conditions Units

Typ

(Note 7)

I

DD

V

OS

P

o

Supply Current VIN= 0V, IO= 0A 1.3 mA (max)

Input Offset Voltage VIN= 0V 5 mV (max)

Output Power THD+N = 0.1%,f=1kHz

R

=16Ω 20 mW

L

R

=32Ω 16 mW

L

Limit

(Note 8)

THD+N = 10%,f=1kHz

R

=16Ω 34 mW

L

R

=32Ω 24 mW

L

Note 2: All voltages are measured with respect to the ground pin, unless otherwise specified.

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 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 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
allowable power dissipation is P
mounted, is 210˚C/W for package MUA08A and 170˚C/W for package M08A.

Note 5: Human body model, 100pF discharged through a 1.5kΩ resistor.

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

Note 7: Typicals are measured at 25˚C and represent the parametric norm.

Note 8: Tested 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 9: The given θ
that of the Exposed-DAP itself.

Note 10: The given θ

is for an LM4908 packaged in an LQB08A with the Exposed-DAP soldered to a printed circuit board copper pad with an area equivalent to

JA

is for an LM4908 packaged in an LQB08A with the Exposed-DAP not soldered to any printed circuit board copper.

JA

DMAX

=(T

)/θJA. For the LM4908, T

JMAX−TA

= 150˚C, and the typical junction-to-ambient thermal resistance, when board

JMAX

, θJA, and the ambient temperature TA. The maximum

JMAX

(Limits)

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External Components Description (Figure 1)

Components Functional Description

1. R

i

The inverting input resistance, along with Rf, set the closed-loop gain. Ri, along with Ci, form a high
pass filter with f

= 1/(2πRiCi).

c

The input coupling capacitor blocks DC voltage at the amplifier’s input terminals. Ci, along with Ri,

2. C

i

create a highpass filter with f

= 1/(2πRiCi). Refer to the section, Selecting Proper External

C

Components, for an explanation of determining the value of C

3. R

4. C

f

S

The feedback resistance, along with Ri, set closed-loop gain.

This is the supply bypass capacitor. It provides power supply filtering. Refer to the Application
Information section for proper placement and selection of the supply bypass capacitor.

This is the half-supply bypass pin capacitor. It provides half-supply filtering. Refer to the section,

5. C

6. C

7. R

B

O

B

Selecting Proper External Components, for information concerning proper placement and selection

.

of C

B

This is the output coupling capacitor. It blocks the DC voltage at the amplifier’s output and forms a high
pass filter with R

at fO= 1/(2πRLCO)

L

This is the resistor which forms a voltage divider that provides 1/2 VDDto the non-inverting input of the
amplifier.

Typical Performance Characteristics

LM4908

.

i

THD+N vs Frequency

= 2.6V, PWR = 15mW, RL=8Ω

V

DD

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THD+N vs Frequency

VDD= 2.6V, PWR = 15mW, RL=16Ω

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Typical Performance Characteristics (Continued)

LM4908

THD+N vs Frequency

V

= 2.6V, PWR = 15mW, RL=32Ω

DD

THD+N vs Frequency

= 3.3V, PWR = 25mW, RL=16Ω

V

DD

THD+N vs Frequency

VDD= 3.3V, PWR = 25mW, RL=8Ω

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THD+N vs Frequency

VDD= 3.3V, PWR = 25mW, RL=32Ω

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THD+N vs Frequency

= 5V, PWR = 50mW, RL=8Ω

V

DD

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THD+N vs Frequency

VDD= 5V, PWR = 50mW, RL=16Ω

Typical Performance Characteristics (Continued)

LM4908

THD+N vs Frequency

V

= 5V, PWR = 50mW, RL=32Ω

DD

THD+N vs Output Power

= 2.6V, RL=8Ω, f = 1kHz

V

DD

THD+N vs Frequency

VDD= 5V, V

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= 3.5Vpp,RL=5kΩ

OUT

THD+N vs Output Power

VDD= 2.6V, RL=16Ω, f = 1kHz

THD+N vs Output Power

= 2.6V, RL=32Ω, f = 1kHz

V

DD

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THD+N vs Output Power

VDD= 3.3V, RL=8Ω, f = 1kHz

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