National Semiconductor LM4926 Technical data

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LM4926 Ground-Referenced, Ultra Low Noise, Fixed Gain, 80mW Stereo Headphone Amplifier

June 2005

General Description

The LM4926 is a ground referenced, fixed-gain audio power amplifier capable of delivering 80mW of continuous average power into a 16Ω single-ended load with less than 1% THD+N from a 3V power supply.

The LM4926 features a new circuit technology that utilizes a charge pump to generate a negative reference voltage. This allows the outputs to be biased about ground, thereby eliminating output-coupling capacitors typically used with normal single-ended loads.

The LM4926 features an Automatic Standby Mode circuitry (patent pending). In the absence of an input signal, after approximately 12 seconds, the LM4926 goes into low current standby mode. The LM4926 recovers into full power operating mode immediately after a signal is applied to either the left or right input pins. This feature saves power supply current in battery operated applications.

Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4926 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 LM4926 features a low-power consumption shutdown mode selectable for either channel separately. This is accomplished by driving either the SD_RC (Shutdown Right Channel) or SD_LC (Shutdown Left Channel) (or both) pins with logic low, depending on which channel is desired shutdown. Additionally, the LM4926 features an internal thermal shutdown protection mechanism.

The LM4926 contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions.

The LM4926 has an internal fixed gain of 1.5V/V.

Key Specifications

Improved PSRR at 217Hz 70dB (typ)

Power Output at VDD= 3V,

=16Ω, THD % 1% 80mW (typ)

Shutdown Current 0.01µA (typ)

Internal Fixed Gain 1.5V/V (typ)

Operating Voltage 1.6V to 4.2V

Features

n Ground referenced outputs n High PSRR n Available in space-saving micro SMD package n Ultra low current shutdown mode n Improved pop & click circuitry eliminates noises during

turn-on and turn-off transitions

n No output coupling capacitors, snubber networks,

bootstrap capacitors, or gain-setting resistors required

n Shutdown either channel independently

Applications

n Notebook PCs n Mobile Phone n PDAs n Portable electronic devices n MP3 Players

Boomer®is a registered trademark of National Semiconductor Corporation.

Typical Application

LM4926

FIGURE 1. Typical Audio Amplifier Application Circuit

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Connection Diagrams

microSMD Package 16 – Bump TL Marking

LM4926

Top View

Order Number LM4926TL

See NS Package Number TLE1411A

Pin Descriptions

Pin Name Function

A1 R_IN Right Channel Input

A2 SGND Signal Ground

A3 CPV

A4 C

B1 SD_RC Active-Low Shutdown, Right Channel

B2 SD_LC Active-Low Shutdown, Left Channel

B4 PGND Power Ground

C1 L_IN Left Channel Input

C2 R_OUT Right Channel Input

C4 C

D1 +AV

D2 L_OUT Left Channel Output

D3 -AV

D4 V

CP+

CP-

CP_OUT

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Top View

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XY – Date Code

TT – Lot Traceability

G – Boomer Family

E8 – LM4926TL

Charge Pump Power Supply

Positive Terminal - Charge Pump Flying Capacitor

Negative Terminal - Charge Pump Flying Capacitor

Positive Power Supply - Amplifier

Negative Power Supply - Amplifier

Charge Pump Power Output

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Absolute Maximum Ratings (Note 2)

If Military/Aerospace specified devices are required,

LM4926

please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Supply Voltage 4.5V

Junction Temperature 150˚C

Thermal Resistance

(typ) TLE1411A (Note 11) 86˚C/W

Operating Ratings

Storage Temperature −65˚C to +150˚C

Input Voltage -0.3V to V

+ 0.3V

Power Dissipation (Note 3) Internally Limited

ESD Susceptibility (Note 4) 2000V

Temperature Range

≤ TA≤ T

MIN

MAX

Supply Voltage (V

−40˚C ≤ TA≤ 85˚C

) 1.6V ≤ VDD≤ 4.2V

ESD Susceptibility (Note 5) 200V

Electrical Characteristics VDD=3V(Note 1)

The following specifications apply for VDD= 3V and 16Ω load unless otherwise specified. Limits apply to TA= 25˚C.

Symbol Parameter Conditions LM4926 Units

Quiescent Power Supply Current Auto Standby Mode

Quiescent Power Supply Current Full Power Mode

∆A

THD+N

PSRR

Shutdown Current V

Output Offset Voltage RL=32Ω,VIN= 0V 0.7 5 mV (max)

Voltage Gain –1.5 V/V

Gain Match 1 %

Input Resistance 20

Output Power

Total Harmonic Distortion + Noise

Power Supply Rejection Ratio Full Power Mode

SNR Signal-to-Noise Ratio

Shutdown Input Voltage High

Shutdown Input Voltage Low

Wake Up Time From Shutdown 5 µs

VIN= 0V, inputs terminated both channels enabled

= 0V, inputs terminated

both channels enabled

= 0V, inputs terminated

one channel enabled

SD_LC

= GND 0.1 1.8 µA (max)

SD_RC

THD+N = 1% (max); f = 1kHz,

=16Ω, one channel

THD+N = 1% (max); f = 1kHz, RL=32Ω, one channel

THD+N = 1% (max); f = 1kHz,

=16Ω, (two channels in phase)

THD+N = 1% (max); f = 1kHz, RL=32Ω, (two channels in phase)

= 60mW, f = 1kHz, RL=16Ω

single channel

= 50mW, f = 1kHz, RL=32Ω

single channel

= 200mVp-p, Input Referred

RIPPLE

f = 217Hz 70

f = 20kHz 50

=32Ω,P

OUT

= 20mW, (A-weighted) f = 1kHz, BW = 20Hz to 22kHz

0.7*CPV

0.3*CPV

Typ

(Note 6)

2.3 mA

7 10 mA (max)

5mA

80 mW

65 mW

43 38 mW (min)

50 45 mW (min)

0.04

0.03

100 dB

Limit

(Notes 7, 8)

15 25

(Limits)

kΩ (min)

kΩ (max)

dBf = 1kHz 65

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Electrical Characteristics VDD=3V(Note 1) (Continued)

The following specifications apply for VDD= 3V and 16Ω load unless otherwise specified. Limits apply to TA= 25˚C.

Symbol Parameter Conditions LM4926 Units

Typ

(Note 6)

=16Ω,PO= 1.6mW,

TALK

OUT

IN THRESH

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 that 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 T allowable power dissipation is P de-rating currents 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 specification limits are guaranteed by design, test, or statistical analysis.

Note 9: If the product is in shutdown mode and V

circuits. If the source impedance limits the current to a max of 10mA, then the part will be protected. If the part is enabled when V performance will be curtailed or the part may be permanently damaged.

Note 10: Human body model, 100pF discharged through a 1.5kΩ resistor.

Note 11: θ

Crosstalk

Output Impedance

Input Leakage

Input Voltage Threshold 2.8 mVp

=(T

DMAX

value is measured with the device mounted on a PCB with a 3” x 1.5”, 1oz copper heatsink.

JMAX-TA

f = 1kHz

Input Terminated Input not terminated

, θJA, and the ambient temperature, TA. The maximum

)/θJAor the number given in Absolute Maximum Ratings, whichever is lower. For the LM4926, see power

exceeds 4.2V (to a max of 4.5V VDD), then most of the excess current will flow through the ESD protection

JMAX

60 dB

∞

0.1 nA

Limit

(Notes 7, 8)

is above 4.5V, circuit

(Limits)

LM4926

kΩ

External Components Description (Figure 1)

Components Functional Description

1. C

2. C

3. C

4. C

5. C

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

high-pass filter with R an explanation of how to determine the value of C

Flying capacitor. Low ESR ceramic capacitor (≤100mΩ)

Output capacitor. Low ESR ceramic capacitor (≤100mΩ)

Tantalum capacitor. Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply

at fC= 1/(2πRiCi). Refer to the section Proper Selection of External Components, for

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

Ceramic capacitor. 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.

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Typical Performance Characteristics

LM4926

THD+N vs Frequency

= 1.6V, RL=16Ω,PO= 1mW

THD+N vs Frequency

VDD= 1.6V, RL=32Ω,PO= 1mW

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THD+N vs Frequency

= 1.8V, RL=16Ω,PO= 5mW

THD+N vs Frequency

VDD= 1.8V, RL=32Ω,PO= 5mW

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Typical Performance Characteristics (Continued)

LM4926

THD+N vs Frequency

= 3V, RL=16Ω,PO= 50mW

THD+N vs Frequency

= 3.6V, RL=16Ω,PO= 100mW

THD+N vs Frequency

VDD= 3V, RL=32Ω,PO= 50mW

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THD+N vs Frequency

VDD= 3.6V, RL=32Ω,PO= 100mW

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