Texas Instruments LM4910 Boomer User manual

LM4910

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SNAS151G –MAY 2004–REVISED MARCH 2007

LM4910 Output Capacitor-less Stereo 35mW Headphone

Amplifier

Check for Samples: LM4910

1FEATURES • Available in space-saving MSOP, LLP, and

SOIC packages

2• Eliminates headphone amplifier output

coupling capacitors APPLICATIONS

• Eliminates half-supply bypass capacitor • Mobile Phones

• Advanced pop & click circuitry eliminates • PDAs

noises during turn-on and turn-off • Portable electronics devices

• Ultra-low current shutdown mode • Portable MP3 players

• Unity-gain stable

• 2.2V - 5.5V operation

DESCRIPTION

The LM4910 is an audio power amplifier primarily designed for headphone applications in portable device

applications. It is capable of delivering 35mW of continuous average power to a 32Ωload with less than 1%

distortion (THD+N) from a 3.3VDC power supply.

The LM4910 utilizes a new circuit topology that eliminates output coupling capacitors and half-supply bypass

capacitors. The LM4910 contains advanced pop & click circuitry which eliminates noises caused by transients

that would otherwise occur during turn-on and turn-off.

Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal

amount of external components. Since the LM4910 does not require any output coupling capacitors, half-supply

bypass capacitors, or bootstrap capacitors, it is ideally suited for low-power portable applications where minimal

space and power consumption are primary requirements.

The LM4910 features a low-power consumption shutdown mode, activated by driving the shutdown pin with logic

low. Additionally, the LM4910 features an internal thermal shutdown protection mechanism. The LM4910 is also

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

Table 1. Key Specifications

VALUE UNIT

PSRR at f = 217Hz 65 dB (typ)

Power Output at VDD = 3.3V, RL= 32Ω, and THD ≤1% 35 mW (typ)

Shutdown Current 0.1 µA (typ)

1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

LM4910

SNAS151G –MAY 2004–REVISED MARCH 2007

www.ti.com

Typical Application

Figure 1. Typical Audio Amplifier Application Circuit

Connection Diagram

Figure 2. MSOP/SO Package Top View

Figure 3. MSOP Marking Top View

G - Boomer Family

C2 - LM4910MM

Figure 4. SO Marking Top View

TT - Die Traceability

Bottom 2 lines - Part Number

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SNAS151G –MAY 2004–REVISED MARCH 2007

Figure 5. LLP Package Top View

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

Absolute Maximum Ratings (1)

Supply Voltage (2) 6.0V

Storage Temperature −65°C to +150°C

Input Voltage -0.3V to VDD + 0.3V

Power Dissipation (3) Internally Limited

ESD Susceptibility Pin 6 (4) 10kV

ESD Susceptibility (5) 2000V

ESD Susceptibility (6) 200V

Junction Temperature 150°C

Thermal Resistance

θJC (MSOP) 56°C/W

θJA (MSOP) 190°C/W

θJC (SOP) 35°C/W

θJA (SOP) 150°C/W

θJC (LQ) 57°C/W

θJA (LQ) 140°C/W

(1) 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.

(2) 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 part will be protected. If the part is enabled

when VDD is above 6V circuit performance will be curtailed or the part may be permanently damaged.

(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 LM4910, see power derating currents for more information.

(4) Human body model, 100pF discharged through a 1.5kΩresistor, Pin 6 to ground.

(5) Human body model, 100pF discharged through a 1.5kΩresistor.

(6) Machine Model, 220pF-240pF discharged through all pins.

Operating Ratings

Temperature Range

TMIN ≤TA≤TMAX −40°C ≤TA≤85°C

Supply Voltage (VDD) 2.2V ≤VCC ≤5.5V

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SNAS151G –MAY 2004–REVISED MARCH 2007

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Electrical Characteristics VDD = 3.3V (1) (2)

The following specifications apply for VDD = 3.3V, AV= 1, and 32Ωload unless otherwise specified. Limits apply to TA= 25°C.

Symbol Parameter Conditions LM4910 Units

(Limits)

Typ Limit

(3) (4) (5)

IDD Quiescent Power Supply Current VIN = 0V, 32ΩLoad 3.5 6 mA (max)

ISD Standby Current VSHUTDOWN = GND 0.1 1.0 µA (max)

VOS Output Offset Voltage 5 30 mV (max)

POOutput Power THD = 1% (max); f = 1kHz 35 30 mW (min)

THD+N Total Harmonic Distortion + Noise PO= 30mWrms; f = 1kHz 0.3 %

65 (f =

VRIPPLE = 200mVp-p sinewave 217Hz)

PSRR Power Supply Rejection Ratio dB

Input terminated with 10Ωto ground 65 (f =

1kHz)

VIH Shutdown Input Voltage High 1.5 V (min)

VIL Shutdown Input Voltage Low 0.4 V (max)

(1) All voltages are measured with respect to the GND pin unless otherwise specified.

(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.

(3) Typicals are measured at 25°C and represent the parametric norm.

(4) Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).

(5) Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

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SNAS151G –MAY 2004–REVISED MARCH 2007

Electrical Characteristics VDD = 3V (1) (2)

The following specifications apply for VDD = 3V, AV= 1, and 32Ωload unless otherwise specified. Limits apply to TA= 25°C.

Symbol Parameter Conditions LM4910 Units

(Limits)

Typ Limit

(3) (4) (5)

IDD Quiescent Power Supply Current VIN = 0V, 32ΩLoad 3.3 6 mA (max)

ISD Standby Current VSHUTDOWN = GND 0.1 1.0 µA (max)

VOS Output Offset Voltage 5 30 mV (max)

POOutput Power THD = 1% (max); f = 1kHz 30 25 mW (min)

THD+N Total Harmonic Distortion + Noise PO= 25mWrms; f = 1kHz 0.3 %

65 (f = 217

VRIPPLE = 200mVp-p sinewave Hz)

PSRR Power Supply Rejection Ratio dB

Input terminated with 10Ωto ground 65 (f =

1kHz)

VIH Shutdown Input Voltage High 1.5 V (min)

VIL Shutdown Input Voltage Low 0.4 V (max)

(1) All voltages are measured with respect to the GND pin unless otherwise specified.

(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.

(3) Typicals are measured at 25°C and represent the parametric norm.

(4) Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).

(5) Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Product Folder Links: LM4910

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SNAS151G –MAY 2004–REVISED MARCH 2007

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Electrical Characteristics VDD = 2.6V (1) (2)

The following specifications apply for VDD = 2.6V, AV= 1, and 32Ωload unless otherwise specified. Limits apply to TA= 25°C.

Symbol Parameter Conditions LM4910 Units

(Limits)

Typ Limit

(3) (4) (5)

IDD Quiescent Power Supply Current VIN = 0V, 32ΩLoad 3.0 mA (max)

ISD Standby Current VSHUTDOWN = GND 0.1 µA (max)

VOS Output Offset Voltage 5 mV (max)

POOutput Power THD = 1% (max); f = 1kHz 13 mW

THD+N Total Harmonic Distortion + Noise PO= 10mWrms; f = 1kHz 0.3 %

55 (f =

VRIPPLE = 200mVp-p sinewave 217Hz)

PSRR Power Supply Rejection Ratio dB

Input terminated with 10Ωto ground 55 (f =

1kHz)

(1) All voltages are measured with respect to the GND pin unless otherwise specified.

(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.

(3) Typicals are measured at 25°C and represent the parametric norm.

(4) Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).

(5) Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

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 Ciat fc= 1/(2πRiCi).

2. CIInput coupling capacitor which blocks the DC voltage at the amplifier's input terminals. Also creates a high-pass filter

with Riat fc= 1/(2πRiCi). 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.

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SNAS151G –MAY 2004–REVISED MARCH 2007

Typical Performance Characteristics

THD+N THD+N

vs vs

Frequency Frequency

THD+N THD+N

vs vs

Frequency Frequency

THD+N THD+N

vs vs

Frequency Frequency

THD+N THD+N

vs vs

Output Power Output Power

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Typical Performance Characteristics (continued)

THD+N THD+N

vs vs

Output Power Output Power

THD+N THD+N

vs vs

Output Power Output Power

Output Power

vs Output Power vs

Load Resistance Load Resistance

Output Power vs Output Power vs

Load Resistance Supply Voltage

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Typical Performance Characteristics (continued)

Output Power vs Power Dissipation vs

Supply Voltage Output Power

Power Dissipation vs Power Dissipation vs

Output Power Output Power

Channel Separation Power Supply Rejection Ratio

Power Supply Rejection Ratio Power Supply Rejection Ratio

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SNAS151G –MAY 2004–REVISED MARCH 2007

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Typical Performance Characteristics (continued)

Open Loop Frequency Response Noise Floor

Frequency Response vs Supply Current vs

Input Capacitor Size Supply Voltage

Application Information

ELIMINATING OUTPUT COUPLING CAPACITORS

Typical single-supply audio amplifiers that drive single-ended (SE) headphones use a coupling capacitor on each

SE output. This output coupling capacitor blocks the half-supply voltage 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 LM4910 eliminates these output coupling capacitors. Amp3 is internally configured to apply a bandgap

referenced voltage (VREF = 1.58V) to a stereo headphone jack's sleeve. This voltage matches the quiescent

voltage present on the Amp1 and Amp2 outputs that drive the headphones. The headphones operate in a

manner 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.

The headphone jack's sleeve is not connected to circuit ground. Using the headphone output jack as a line-level

output will place the LM4910's bandgap referenced voltage on a plug's sleeve connection. This presents no

difficulty when the external equipment uses capacitively coupled inputs. For the very small minority of equipment

that is DC-coupled, the LM4910 monitors the current supplied by the amplifier that drives the headphone jack's

sleeve. If this current exceeds 500mAPK, the amplifier is shutdown, protecting the LM4910 and the external

equipment.

ELIMINATING THE HALF-SUPPLY BYPASS CAPACITOR

Typical single-supply audio amplifers are normally biased to 1/2VDD in order to maximize the output swing of the

audio signal. This is usually achieved with a simple resistor divider network from VDD to ground that provides the

proper bias voltage to the amplifier. However, this scheme requires the use of a half-supply bypass capacitor to

improve the bias voltage's stability and the amplifier's PSRR performance.

The LM4910 utilizes an internally generated, buffered bandgap reference voltage as the amplifier's bias voltage.

This bandgap reference voltage is not a direct function of VDD and therefore is less susceptible to noise or ripple

on the power supply line. This allows for the LM4910 to have a stable bias voltage and excellent PSRR

performance even without a half-supply bypass capacitor.

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