Datasheet LM49270SQX, LM49270 Datasheet (NSC)

December 2006

LM49270 
Filterless 2.2W Stereo Class D Audio Subsystem with OCL
Headphone Amplifier, 3D Enhancement, and Headphone
Sense

General Description

The LM49270 is a fully integrated audio subsystem designed
for stereo multimedia applications. The LM49270 combines a

2.2W stereo Class D amplifier with a 155mW stereo head­phone amplifier, volume control, headphone sense, and
National’s unique 3D sound enhancement into a single de­vice. The LM49270 uses flexible I2C control interface for
multiple application requirements.

The filterless stereo class D amplifiers delivers 2.2W/channel
into a 4Ω load with less than 10% THD+N with a 5V supply.
The headphone amplifier features National’s Output Capaci­tor-less (OCL) architecture that eliminates the output coupling
capacitors required by traditional headphone amplifiers.

The IC features a headphone sense input (HPS) that auto­matically detects the presence of a headphone and config­ures the device accordingly. The LM49270 can automatically
switch from OCL headphone output to a line driver output. If
the VOC pin is pulled to GND, the VOC amplifier is disabled
and the VOC pin is internally set to GND. This feature allows
the LM49270 to be used as a line driver in OCL mode without
a GND conflict on the headphone jack sleeve. Additionally,
the headphone amplifier can be configured as capacitively
coupled (CC).

The LM49270 features a 32 step volume control for the head­phone and stereo outputs. The device mode select and vol­ume are controlled through an I2C compatible interface.

Output short circuit and thermal shutdown protection prevent
the device from being damaged during fault conditions. Su­perior click and pop suppression eliminates audible transients
on power-up/down and during shutdown. The LM49270 is
available in a space saving 28-pin, 5x5mm LLP package.

Key Specifications

■ Stereo Class D Amplifier Efficiency:

 V

DD

= 3.3V, 450mW/Ch into 8Ω

84%

 V

DD

= 5V, 1W/Ch into 8Ω

84%

■ Quiescent Power Supply Current, V

DD

= 3.3V

 Speaker Mode 5.5mA

 Headphone Mode (OCL) 4mA

■ Power Output/Channel, V

DD

= 5V

 Class D Speaker amplifier:

RL = 4Ω, THD+N = ≤ 10%

2.2W

RL = 8Ω, THD+N = ≤ 1%

1.06W

 Headphone amplifier:

RL = 16Ω, THD+N = ≤ 1%

155mW

RL = 32Ω, THD+N = ≤ 1%

90mW

■ Shutdown current

0.02μA

Features

■

Stereo filterless Class D amplifier

■

Selectable OCL/CC headphone amplifier

■

Headphone sense ability

■

National’s 3D Enhancement

■

RF suppression

■

I2C control interface

■

32-step digital volume control

■

6 Operating Modes

■

Output short circuit protection and thermal shutdown
protection

■

Minimum external components

■

Click and Pop suppression

■

Micro-power shutdown

■

Independent speaker and headphone volume controls

■

Available in space-saving 28 pin LLP package

Applications

■

Portable DVD players

■

Smart phones

■

PDAs

■

Laptops

Boomer® is a registered trademark of National Semiconductor Corporation.

© 2007 National Semiconductor Corporation 202129 www.national.com

LM49270 Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D

Enhancement, and Headphone Sense

Typical Application

20212994

FIGURE 1. Typical Audio Amplifier Application Circuit

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LM49270

Connection Diagrams

SQ Package

5mm x 5mm x 0.8mm

20212990

Top View

Order Number LM49270SQ

See NS Package Number NSQAQ028

SQ Markings

20212901

Top View

NS = National Logo

U = Fab Code

Z = Assembly Plant

XY = 2 Digit date code

TT = Die Traceability

49270SQ = LM49270SQ

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LM49270

TABLE 1. Pin Descriptions

PIN NAME DESCRIPTION

1 RHP Right channel headphone output

2 VOC VDD/2 buffer output

3 LHP Left channel headphone output

4 HPV

DD

Headphone supply input

5 R3DIN Right channel 3D input

6 L3DIN Left channel 3D input

7 BYPASS Bias bypass

8 LIN Left channel input

9 RIN Right channel input

10 GND Analog ground

11 NC No connect

12 LSV

DD

Speaker supply voltage input

13 RLS+ Right channel non-inverting speaker output

14 RLS- Right channel inverting speaker output

15 NC No connect

16 NC No connect

17 I2CV

DD

I2C supply voltage input

18 LSGND Speaker ground

19 V

DD

Power supply

20 ADR Address

21 NC No connect

22 LLS- Left channel inverting speaker output

23 LLS+ Left channel non-inverting speaker output

24 LSV

DD

Speaker supply voltage input

25 SDA Serial data input

26 SCL Serial clock input

27 HPS Headphone sense input

28 GND Headphone ground

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LM49270

Absolute Maximum Ratings (Notes 1, 2)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Supply Voltage (Note 1) 6.0V
Storage Temperature −65°C to +150°C
Input Voltage –0.3V to VDD +0.3V

Power Dissipation (Note 3) Internally Limited
ESD Susceptibility(Note 4) 2000V
ESD Susceptibility (Note 5) 200V
Junction Temperature (T

JMAX

)

150°C

Thermal Resistance

 θ

JA

35.1°C/W

Operating Ratings (Notes 1, 2)

Temperature Range

T

MIN

≤ TA ≤ T

MAX

−40°C ≤ TA ≤ 85°C

Supply Voltage
(VDD, LSVDD, HPVDD)

2.4V ≤ VDD ≤ 5.5V

I2C Voltage (I2CVDD)

2.4V ≤ I2CVDD ≤ 5.5V

Electrical Characteristics VDD = 3.3V (Notes 1, 2) The following specifications apply for Headphone:

AV = 0dB, R

L(HP)

= 32Ω; for Loudspeakers: AV = 6dB, R

L(SP)

= 15μH + 8Ω + 15μH , f = 1kHz, unless otherwise specified. Limits

apply for TA = 25°C.

Symbol Parameter Conditions

LM49270

Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

I

DD

Supply Current

VIN = 0, RL = No Load,
Both channels active
Speaker ON, HP OFF
Speaker OFF, CC HP ON
Speaker OFF, OCL HP ON

5.5
3
4

7.6

4.7

5.75

mA (max)
mA (max)
mA (max)

I

SD

Shutdown Supply Current 0.02 2

μA (max)

V

OS

Output Offset Voltage

Headphone
Speaker

10
10

25
60

mV (max)
mV (max)

P

OUT

Output Power

Speaker Mode, f = 1kHz

THD+N = 1%

RL = 4Ω

RL = 8Ω

700
450 400

mW

mW (min)

THD+N = 10%

RL = 4Ω

RL = 8Ω

870
560

mW
mW

CC Headphone Mode, f = 1kHz

THD+N = 1%

RL = 16Ω

RL = 32Ω

60
36 30

mW

mW (min)

THD+N = 10%

RL = 16Ω

RL = 32Ω

74
55

mW
mW

OCL Headphone Mode, f = 1kHz

THD+N = 1%

RL = 16Ω

RL = 32Ω

60
36 30

mW

mW (min)

THD+N = 10%

RL = 16Ω

RL = 32Ω

73
55

mW
mW

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LM49270

Symbol Parameter Conditions

LM49270

Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

THD+N Total Harmonic Distortion + Noise

Speaker Mode, f = 1kHz

P

OUT

= 100mW, RL = 8Ω

0.02

%

CC Headphone Mode,
f = 1kHz

P

OUT

= 12mW, RL = 32Ω

0.015

%

OCL Headphone Mode,
f = 1kHz

P

OUT

= 12mW, RL = 32Ω

0.02

%

e

N

Noise

Speaker Mode,
A-Wtg, Input Referred

47

μV

CC Headphone Mode,
A-Wtg, Input Referred

10

μV

OCL Headphone Mode, A-Wtg,
Input Referred

11

μV

η

Efficiency

Speaker Mode

RL = 8Ω

84 %

Xtalk Crosstalk

Speaker Mode,
f = 1kHz, VIN = 1Vp-p

71 dB

CC Headphone Mode,
f = 1kHz, VIN = 1Vp-p

70 dB

OCL Headphone Mode,
f = 1kHz, VIN = 1Vp-p

55 dB

T

ON

Turn-on Time

30 ms

T

OFF

Turn-off Time

64 ms

Z

IN

Input Impedance

Maximum Gain

23.5

kΩ

Minimum Gain

210

kΩ

A

V

Gain

Maximum Gain, Speaker Mode 30 dB

Minimum Gain, Speaker Mode –47 dB

Maximum Gain, Headphone Mode 18 dB

Minimum Gain, Headphone Mode –59 dB

PSRR Power Supply Rejection Ratio

Speaker Mode,
V

RIPPLE

= 200mVp-p Sine
f = 217Hz
f = 1kHz

68
68

dB
dB

Headphone Mode,
V

RIPPLE

= 200mVp-p Sine, CC
Mode
f = 217Hz
f = 1kHz

73
73

dB
dB

Headphone Mode,
V

RIPPLE

= 200mVp-p Sine, OCL
Mode
f = 217Hz
f = 1kHz

75
79

dB
dB

HPS

(Th)

Headphone Sense Threshold

Detect Headphone 2.9 V (min)

Detect no Headphone 1.8 V (max)

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LM49270

Electrical Characteristics VDD = 5.0V (Notes 2, 1) The following specifications apply for Headphone”

AV = 0dB, R

L(HP)

= 32Ω,: for Loudspeakers: AV = 6dB, R

L(SP

) = 15μH + 8Ω + 15μH, f = 1kHz unless otherwise specified. Limits

apply for TA = 25°C.

Symbol Parameter Conditions

LM49270

Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

I

DD

Supply Current

VIN = 0, RL = No Load,
Both channels active
Speaker ON, HP OFF
Speaker OFF, CC HP ON
Speaker OFF, OCL HP ON

8.5

3.6

4.7

12.4

5.5

6.5

mA (max)
mA (max)
mA (max)

I

SD

Shutdown Supply Current 0.15 2

μA (max)

V

OS

Output Offset Voltage

Headphone
Speaker

10
10

25
60

mV (max)
mV (max)

P

OUT

Output Power

Speaker Mode, f = 1kHz,

THD+N = 1%

RL = 4Ω

RL = 8Ω

1.75

1.06

W
W

THD+N = 10 %

RL = 4Ω

RL = 8Ω

2.2

1.35

W
W

CC Headphone Mode, f = 1kHz,

THD+N = 1%

RL = 16Ω

RL = 32Ω

155

90

mW
mW

THD+N = 10%

RL = 16Ω

RL = 32Ω

177
140

mW
mW

OCL Headphone Mode, f = 1kHz,

THD+N = 1%

RL = 16Ω

RL = 32Ω

155

90

mW
mW

THD+N = 10%

RL = 16Ω

RL = 32Ω

175
140

mW
mW

THD+N

Total Harmonic Distortion +
Noise

Speaker Mode, f = 1kHz

P

OUT

= 100mW, RL = 8Ω

0.03

%

CC Headphone Mode,
f = 1kHz

P

OUT

= 12mW, RL = 32Ω

0.02

%

OCL Headphone Mode,
f = 1kHz

P

OUT

= 12mW, RL = 32Ω

0.03

%

e

N

Noise

Speaker Mode,
A-Wtg, Input Referred

47

μV

CC Headphone Mode,
A-Wtg, Input Referred

10

μV

OCL Headphone Mode,
A-Wtg, Input Referred

11

μV

η

Efficiency

Speaker Mode

RL = 8Ω

84 %

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LM49270

Symbol Parameter Conditions

LM49270

Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

Xtalk Crosstalk

Speaker Mode,
f = 1kHz, VIN = 1Vp-p

–85 dB

CC Headphone Mode,
f = 1kHz, VIN = 1Vp-p

–70 dB

OCL Headphone Mode,
f = 1kHz, VIN = 1Vp-p

–58 dB

T

ON

Turn-on Time

43 ms

T

OFF

Turn-off Time

100 ms

Z

IN

Input Impedance

Maximum Gain

23.5

kΩ

Minimum Gain

210

kΩ

A

V

Gain

Maximum Gain, Speaker Mode 30 dB

Minimum Gain, Speaker Mode –47 dB

Maximum Gain, Headphone Mode 18 dB

Minimum Gain, Headphone Mode –59 dB

PSRR Power Supply Rejection Ratio

Speaker Mode,
V

RIPPLE

= 200mVp-p Sine
f = 217Hz
f = 1kHz

61
61

dB
dB

Headphone Mode,
V

RIPPLE

= 200mVp-p Sine, CC
Mode
f = 217Hz
f = 1kHz

75
74

dB

min

Headphone Mode,
V

RIPPLE

= 200mVp-p Sine, OCL
Mode
f = 217Hz
f = 1kHz

78
75

dB
dB

HPS

(Th)

Headphone Sense Threshold

Detect Headphone 4.4 V (min)

Detect no Headphone 3 V (max)

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 T

JMAX

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

allowable power dissipation is P

DMAX

= (T

JMAX

– TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM49270 see power

derating 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.

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LM49270

Typical Performance Characteristics

THD+N vs Output Power

Speaker Mode

AV = 6dB, RL = 4Ω, f = 1kHz

20212902

THD+N vs Output Power

Speaker Mode

AV = 6dB, RL = 8Ω, f = 1kHz

20212903

THD+N vs Output Power

OCL Headphone Mode

AV = 0dB, RL = 16Ω, f = 1kHz

20212908

THD+N vs Output Power

OCL Headphone Mode

AV = 0dB, RL = 32Ω, f = 1kHz

20212909

THD+N vs Output Power

CC Headphone Mode

AV = 0dB, RL = 16Ω, f = 1kHz

20212914

THD+N vs Output Power

CC Headphone Mode

AV = 0dB, RL = 32Ω, f = 1kHz

20212915

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LM49270

THD+N vs Frequency

Speaker Mode

VDD = 3.3V, P

OUT

= 300mW, RL = 4Ω

20212904

THD+N vs Frequency

Speaker Mode

VDD = 5V, P

OUT

= 500mW, RL = 4Ω

20212905

THD+N vs Frequency

Speaker Mode

VDD = 3.3V, P

OUT

= 200mW, RL = 8Ω

20212906

THD+N vs Frequency

Speaker Mode

VDD = 5V, P

OUT

= 350mW, RL = 8Ω

20212907

THD+N vs Frequency

OCL Headphone Mode

VDD = 3.3V, P

OUT

= 45mW, RL = 16Ω

20212910

THD+N vs Frequency

OCL Headphone Mode

VDD = 5V, P

OUT

= 100mW, RL = 16Ω

20212911

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LM49270

THD+N vs Frequency

OCL Headphone Mode

VDD = 3.3V, P

OUT

= 25mW, RL = 32Ω

20212912

THD+N vs Frequency

OCL Headphone Mode

VDD = 5V, P

OUT

= 70mW, RL = 32Ω

20212913

THD+N vs Frequency
CC Headphone Mode

VDD = 3.3V, P

OUT

= 45mW, RL = 16Ω

20212916

THD+N vs Frequency
CC Headphone Mode

VDD = 5V, P

OUT

= 100mW, RL = 16Ω

20212917

THD+N vs Frequency
CC Headphone Mode

VDD = 3.3V, P

OUT

= 25mW, RL = 32Ω

20212918

THD+N vs Frequency
CC Headphone Mode

VDD = 5V, P

OUT

= 70mW, RL = 32Ω

20212919

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LM49270

PSRR vs Frequency

Speaker Mode

VDD = 3.3V, V

RIPPLE

= 200mV

P-P

, RL = 8Ω

202129a2

PSRR vs Frequency

OCL Headphone Mode

VDD = 3.3V, V

RIPPLE

= 200mV

P-P

, RL = 32Ω

202129a3

PSRR vs Frequency

CC Headphone Mode

VDD = 3.3V, V

RIPPLE

= 200mV

P-P

, RL = 32Ω

202129a4

Efficiency vs Output Power

Speaker Mode

RL = 4Ω, f = 1kHz

20212967

Efficiency vs Output Power

Speaker Mode

RL = 8Ω, f = 1kHz

20212968

Power Dissipation vs Output Power

Speaker Mode

RL = 4Ω, f = 1kHz

20212969

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LM49270

Power Dissipation vs Output Power

Speaker Mode

RL = 8Ω, f = 1kHz

20212970

Power Dissipation vs Output Power

OCL Headphone Mode

RL = 16Ω, f = 1kHz

20212998

Power Dissipation vs Output Power

OCL Headphone Mode

RL = 32Ω, f = 1kHz

20212977

Power Dissipation vs Output Power

CC Headphone Mode

RL = 16Ω, f = 1kHz

20212982

Power Dissipation vs Output Power

CC Headphone Mode

RL = 32Ω, f = 1kHz

20212983

Output Power vs Supply Voltage

Speaker Mode

RL = 4Ω, f = 1kHz

20212971

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LM49270

Output Power vs Supply Voltage

Speaker Mode

RL = 8Ω, f = 1kHz

20212972

Output Power vs Supply Voltage

OCL Headphone Mode

RL = 16Ω, f = 1kHz

20212995

Output Power vs Supply Voltage

OCL Headphone Mode

RL = 32Ω, f = 1kHz

20212996

Output Power vs Supply Voltage

CC Headphone Mode

RL = 16Ω, f = 1kHz

20212997

Output Power vs Supply Voltage

CC Headphone Mode

RL = 32Ω, f = 1kHz

20212985

Crosstalk vs Frequency

Speaker Mode

VDD = 3.3V, V

RIPPLE

= 1V

P-P

, RL = 8Ω

202129a0

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LM49270

Crosstalk vs Frequency

OCL Headphone Mode

VDD = 3.3V, V

RIPPLE

= 1V

P-P

, RL = 32Ω

20212989

Crosstalk vs Frequency

CC Headphone Mode

VDD = 3.3V, V

RIPPLE

= 1V

P-P

, RL = 32Ω

202129a1

Supply Current vs Supply Voltage

Speaker Mode, No Load

20212975

Supply Current vs Supply Voltage

OCL Headphone Mode, No Load

20212981

Supply Current vs Supply Voltage

CC Headphone Mode, No Load

20212988

Turn-On

Speaker Mode

20212927

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LM49270

Turn-Off

Speaker Mode

20212928

Turn-On

OCL Headphone Mode

20212929

Turn-Off

OCL Headphone Mode

20212930

Turn-On

CC Headphone Mode

20212931

Turn-Off

CC Headphone Mode

20212932

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LM49270

Application Information

I2C COMPATIBLE INTERFACE

The LM49270 is controlled through an I2C compatible serial
interface that consists of a serial data line (SDA) and a serial
clock (SCL). The clock line is uni-directional. The data line is
bi-directional (open-collector), although the LM49270 does
not write to the I2C bus. The LM49270 and the master can
communicate at clock rates up to 400kHz. Figure 3 shows the
I2C interface timing diagram. The LM49270 is a transmit/re­ceive slave-only device, reliant upon the master to generate
a clock signal.

The master device communicates to the LM49270 by trans­mitting the proper device address followed by a command

word. Each transmission sequence is framed by a START
condition and a STOP condition. Each word (register address
+ register content) transmitted over the bus is 8 bits long and
is always followed by an acknowledge pulse.

To avoid an address conflict with another device on the I2C
bus, the LM49270 address is determined by the ADR pin, the
state of ADR determines address bit A1 (Table 2). When ADR
= 0, the address is 1111 1000. When ADR = 1 the device
address is 1111 1010.

TABLE 2. Device Address

ADR A7 A6 A5 A4 A3 A2 A1 A0

X 1 1 1 1 1 0 X 0

0 1 1 1 1 1 0 0 0

1 1 1 1 1 1 0 1 0

TABLE 3. I2C Control Registers

REG Register Name D7 D6 D5 D4 D3 D2 D1 D0

0 Shutdown Control 0 0

— —

HP3DSEL LS3DSEL OCL/CC PWR_ON

1 Headphone Gain Control 0 1

—

HP4 HP3 HP2 HP1 HP0

2 Speaker Gain Control 1 0

—

LS4 LS3 LS2 LS1 LS0

Note: OCL/CC = 1 selects OCL mode; OCL/CC = 0 selects
cap coupled mode

PWR_ON = 0 puts part in shutdown

BUS FORMAT

The I2C bus format is shown in Figure 2. The “start” signal is
generated by lowering the data signal while the clock is high.
The start signal alerts all devices on the bus that a device
address is being written to the bus.

The 8-bit device address is written to the bus next, most sig­nificant bit first. The data is latched in on the rising edge of the
clock. Each address bit must be stable while the clock is high.

After the last address bit is sent, the master device releases
the data line, during which time, an acknowledge clock pulse
is generated. If the LM49270 receives the address correctly,
then the LM49270 pulls the data line low, generating an ac­knowledge bit (ACK).

Once the master device has registered the ACK bit, the 8-bit
register address/data word is sent. Each data bit should be
stable while the clock level is high. After the 8–bit word is sent,
the LM49270 sends another ACK bit. Following the acknowl­edgement of the data word, the master device issues a “stop”
bit, allowing SDA to go high while the clock signal is high.

20212991

FIGURE 2. I2C Bus Format

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LM49270

20212992

FIGURE 3. I2C Timing Diagram

GENERAL AMPLIFIER FUNCTION

Class D Amplifier

The LM49270 features a high-efficiency, filterless, Class D
stereo amplifier. The LM49270 Class D amplifiers feature a
filterless modulation scheme known as Class BD. The differ­ential outputs of each channel switch at 300kHz from VDD to
GND. When there is no input signal applied, the two outputs
(LLS+ and LLS-) switch in phase with a 50% duty cycle. Be­cause the outputs of the LM49270 are differential, there is in
no net voltage across the speaker, thus no load current during
the idle state conserving power.

When an input signal is applied, the duty cycle (pulse width)
of each output changes. For increasing output voltages, the
duty cycle of LLS+ increases, while the duty cycle of LLS­decreases. For decreasing output voltages, the converse
occurs. The duty cycle of LLS- increases while the duty cycle
of LLS+ decreases. The difference between the two pulse
widths yields the differential output voltage.

Headphone Amplifier

The LM49270 headphone amplifier features two different op­erating modes, output capacitor-less (OCL) and capacitor
coupled (CC). The OCL architecture eliminates the bulky, ex­pensive output coupling capacitors required by traditional
headphone amplifiers. The LM49270 headphone section us­es three amplifiers. Two amplifiers drive the headphones
while the third (VOC) is set to the internally generated bias
voltage (typically VDD/2). The third amplifier is connected to
the return terminal (sleeve) of the headphone jack. In this
configuration, the signal side of the headphones are biased
to VDD/2, the return is biased to VDD/2, thus there is no net DC
voltage across the headphone eliminating the need for an
output coupling capacitor. Removing the output coupling ca­pacitors from the headphone signal path reduces component
count, reducing system cost and board space consumption,
as well as improving low frequency performance and sound
quality. The voltage on the return sleeve is not an issue when
driving headphones. However, if the headphone output is
used as a line out, the VDD/2 can conflict with the GND po­tential that a line-in would expect on the return sleeve. When
the return of the headphone jack is connected to GND, the
LM49270 detects an output short circuit condition and the
VOC amplifier is disabled preventing damage to the LM49270
and allowing the headphone return to be biased at GND.

Capacitor Coupled Headphone Mode

In capacitor coupled (CC) mode, the VOC pin is disabled, and
the headphone outputs are coupled to the jack through series
capacitors, allowing the headphone return to be connected to
GND (Figure 4). In CC mode, the LM49270 requires output
coupling capacitors to block the DC component of the ampli­fier output, preventing DC current from flowing to the load.
The output capacitor and speaker impedance form a high
pass filter with a -3dB roll-off determined by:

f

-3dB

= 1 / 2πRLC

OUT

Where RL is the headphone impedance, and C

OUT

is the out-

put coupling capacitor. Choose C

OUT

such that f

-3dB

is well

below the lowest frequency of interest. Setting f

-3dB

too high
results in poor low frequency performance. Select capacitor
dielectric types with low ESR to minimize signal loss due to
capacitor series resistance and maximize power transfer to
the load.

20212993

FIGURE 4. Capacitor Coupled Headphone Mode

Headphone Sense

The LM49270 features a headphone sense input (HPS) that
monitors the headphone jack and configures the device de­pending on the presence of a headphone. When the HPS pin
is low, indicating that a headphone is not present, the
LM49270 speaker amplifiers are active and the headphone

www.national.com 18

LM49270

amplifiers are disabled. When the HPS pin is high, indicating
that a headphone is present, the headphone amplifiers are
active while the speaker amplifiers are disabled.

POWER DISSIPATION AND EFFICIENCY

The major benefit of Class D amplifier is increased efficiency
versus Class AB. The efficiency of the LM49270 speaker am­plifiers is attributed to the output transistors’ region of opera­tion. The Class D output stage acts as current steering
switches, consuming negligible amounts of power compared
to their Class AB counterparts. Most of the power loss asso­ciated with the output stage is due to the IR loss of the
MOSFET on-resistance (R

DS(ON)

) , along with the switching

losses due to gate charge.
The maximum power dissipation per headphone channel in

Capacitor Coupled mode is given by:

P

DMAX(CC)

= V

DD

2

/2π2R

L

In OCL mode, the maximum power dissipation increases due
to the use of a third amplifier as a buffer. The power dissipa­tion is given by:

P

DMAX(OCL)

= V

DD

2/π2

R

L

SHUTDOWN FUNCTION

The LM49270 features a shutdown mode configured through
the I2C interface. Bit D0 (PWR_ON) in the Shutdown Control
register shuts down/turns on the entire device. Set PWR_ON
= 1 to enable the LM49270, set PWR_ON = 0 to disable the
device.

AUDIO AMPLIFIER GAIN SETTING

Each channel of the LM49270 features a 32 step volume con­trol. The loudspeaker volume has a range of -47dB to 30dB
and the headphone has a range of -59dB to 18dB (see Table

4).

TABLE 4. Volume Control

Volume Step LS4/HP4 LS3/HP3 LS2/HP2 LS1/HP1 LS0/HP0 LS

Gain (dB)

HP

Gain (dB)

1 0 0 0 0 0 –47 –59

2 0 0 0 0 1 –36 –48

3 0 0 0 1 0 –28.5 –46.5

4 0 0 0 1 1 –22.5 –34.5

5 0 0 1 0 0 –18 –30

6 0 0 1 0 1 –15 –27

7 0 0 1 1 0 –12 –24

8 0 0 1 1 1 –9 –21

9 0 1 0 0 0 –6 –18

10 0 1 0 0 1 –3 –15

11 0 1 0 1 0 –1.5 –13.5

12 0 1 0 1 1 0 –12

13 0 1 1 0 0 1.5 –10.5

14 0 1 1 0 1 3 –9

15 0 1 1 1 0 4.5 –7.5

16 0 1 1 1 1 6 –6

17 1 0 0 0 0 7.5 –4.5

18 1 0 0 0 1 9 –3

19 1 0 0 1 0 10.5 –1.5

20 1 0 0 1 1 12 0

21 1 0 1 0 0 13.5 1.5

22 1 0 1 0 1 15 3

23 1 0 1 1 0 16.5 4.5

24 1 0 1 1 1 18 6

25 1 1 0 0 0 19.5 7.5

26 1 1 0 0 1 21 9

27 1 1 0 1 0 22.5 10.5

28 1 1 0 1 1 24 12

29 1 1 1 0 0 25.5 13.5

30 1 1 1 0 1 27 15

31 1 1 1 1 0 28.5 16.5

32 1 1 1 1 1 30 18

19 www.national.com

LM49270

NATIONAL 3D ENHANCEMENT

The LM49720 features National’s 3D sound enhancement.
3D sound improves the apparent stereo channel separation
whenever the left and right speakers are located close to each
other, widening the perceived sound stage in devices with a
small form factor that prohibits proper speaker placement.

An external RC network , shown in Figure 1, enables the 3D
effect. R3D sets the level of the 3D effect; decreasing the val­ue of R3D will increase the 3D effect. The 3D network acts
like a high pass filter C3D sets the frequency response; in­creasing the value of C3D will decrease the low cutoff fre­quency at which the 3D effect starts to occur, as shown by
this equation:

f

3D(-3dB)

= 1/2π(R3D)(C3D) (1)

Enabling the 3D effect increases the gain by a multiplication
factor of (1 + 20kΩ/R3D). Setting R3D to 20kΩ results in a
6dB increase (doubling) of the gain, increasing the 3D effect.
The level of 3D effect is also dependent on other factors such
as speaker placement and the distance from the speakers to
the listener. The values of R3D and C3D should be chosen
for each application individually, taking into account the phys­ical factors noted before.

POWER SUPPLIES

The LM49270 uses different supplies for each portion of the
device, allowing for the optimum combination of headroom,
power dissipation and noise immunity. The speaker amplifier
gain stage is powered from VDD, while the output stage is
powered from LSVDD. The headphone amplifiers, input am­plifiers and volume control stages are powered from HPVDD.
The separate power supplies allow the speakers to operate
from a higher voltage for maximum headroom, while the
headphones operate from a lower voltage, improving power
dissipation. HPVDD may be driven by a linear regulator to fur­ther improve performance in noisy environments. The I2C
portion if powered from I2CVDD, allowing the I2C portion of the
LM49270 to interface with lower voltage digital controllers.

PROPER SELECTION OF EXTERNAL COMPONENTS

Audio Amplifier Power Supply Bypassing/Filtering

Proper power supply bypassing is critical for low noise per­formance and high PSRR. Place the supply bypass capacitor

as close to the device as possible. Typical applications em­ploy a voltage regulator with 10µF and 0.1µF bypass capac­itors that increase supply stability. These capacitors do not
eliminate the need for bypassing of the LM49270 supply pins.
A 1µF capacitor is recommended.

Bypass Capacitor Selection

The LM49270 generates a VDD/2 common-mode bias voltage
internally. The BYPASS capacitor, CB, improves PSRR and
THD+N by reducing noise at the BYPASS node. Use a 1μF
capacitor, placed as close to the device as possible for CB.

Audio Amplifier Input Capacitor Selection

Input capacitors, CIN, in conjunction with the input impedance
of the LM49270 forms a high pass filter that removes the DC
bias from an incoming signal. The AC-coupling capacitor al­lows the amplifier to bias the signal to an optimal DC level.
Assuming zero source impedance, the -3dB point of the high
pass filter is given by:

f

(–3dB)

= 1/2πRINC

IN

(2)

Choose CIN such that f

-3dB

is well below that lowest frequency

of interest. Setting f

-3dB

too high affects the low-frequency re­sponses of the amplifier. Use capacitors with low voltage
coefficient dielectrics, such as tantalum or aluminum elec­trolytic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low frequen­cies. Other factors to consider when designing the input filter
include the constraints of the overall system. Although high
fidelity audio requires a flat frequency response between
20Hz and 20kHz, portable devices such as cell phones may
only concentrate on the frequency range of the frequency
range of the spoken human voice (typically 300Hz to 4kHz).
In addition, the physical size of the speakers used in such
portable devices limits the low frequency response; in this
case, frequencies below 150Hz may be filtered out.

www.national.com 20

LM49270

Revision Table

Rev Date Description

1.0 12/19/06 Initial release.

21 www.national.com

LM49270

Physical Dimensions inches (millimeters) unless otherwise noted

28 Lead LLP

Order Number LM49270SQ

NS Package Number NSQAQ028

www.national.com 22

LM49270

Notes

23 www.national.com

LM49270

Notes

LM49270 Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D

Enhancement, and Headphone Sense

THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION
(“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY
OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO
SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS,
IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS
DOCUMENT.

TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT
NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL
PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR
APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND
APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE
NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS.

EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO
LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE
AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR
PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY
RIGHT.

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR
SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and
whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected
to result in a significant injury to the user. A critical component is any component in a life support device or system whose failure to perform
can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness.

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Copyright© 2007 National Semiconductor Corporation

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