LM48824TMX - Texas Instruments High-Performance Analog

LM48824

LM48824 Class G Headphone Amplifier with I 2 C Volume Control

Literature Number: SNAS479C

LM48824 August 31, 2009

Class G Headphone Amplifier with I2C Volume Control

General Description

The LM48824 is a Class G, ground-referenced stereo head-

phone amplifier designed for portable devices. The LM48824

features National’s ground-referenced architecture, which

eliminates the large DC blocking capacitors required by tra-

ditional headphone amplifiers, saving board space and mini-

mizing system cost.

The LM48824 takes advantage of National’s patent-pending

Class G architecture offering power savings compared to a

traditional Class AB headphone amplifier. Additionally, output

noise is improved by common-mode sensing that corrects for

any differences between the amplifier ground and the poten-

tial at the headphone return terminal, minimizing noise creat-

ed by any ground mismatches.

A high output impedance mode allows the LM48824's outputs

to be driven by an external source without degrading the sig-

nal. Other features include flexible power supply require-

ments, differential inputs for improved noise rejection, a low

power (2.5μA) shutdown mode, and a 32-step I2C volume

control with mute function.

The LM48824's superior click and pop suppression eliminates

audible transients on power-up/down and during shutdown.

The LM48824 is available in an ultra-small 16-bump, 0.4mm

pitch micro SMD package (1.69mm x 1.69mm)

Key Specifications

■ Quiescent Power Supply Current at 3.6V 0.9mA (typ)

■ Output Power/channel at VDD = 3.6V

RL = 16Ω, THD+N ≤ 1% 37mW (typ)

■ Output Power/channel at VDD = 3.6V

RL = 32Ω, THD+N ≤ 1% 29mW (typ)

■ PSRR at 217Hz 100dB (typ)

■ Shutdown current 2.5μA (typ)

Features

■Class G Power Savings

■Ground Referenced Headphone Outputs – Eliminates

Output Coupling Capacitors

■Common-Mode Sense

■I2C Volume and Mode Control

■High Output Impedance in Shutdown

■Differential Inputs

■Advanced Click-and-Pop Suppression

■Low Supply Current

■Low THD mode option

Applications

■Mobile Phones, PDAs, MP3 Players

■Portable Electronic Devices, Notebook PCs

Simplified Block Diagram

30089221

Boomer® is a registered trademark of National Semiconductor Corporation.

LM48824 Class G Headphone Amplifier with I2C Volume Control

Typical Application

30089270

FIGURE 1. Typical Audio Amplifier Application Circuit

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LM48824

Connection Diagrams

TM Package

1.7mm x 1.7mm x 0.6mm

30089220

Top View

Order Number LM48824TM

See NS Package Number TMD16DDA

16–Bump micro SMD Marking

30089217

Top View

XY = Date code

TT = Die traceability

G = Boomer Family

L6 = LM48824TM

Ordering Information

Order Number Package Package DWG # Transport Media MSL Level Green Status

LM48824TM 16 Bump micro SMD TMD16DDA 250 units on tape and reel 1 NOPB

LM48824TMX 16 Bump micro SMD TMD16DDA 3000 units on tape and reel 1 NOPB

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LM48824

Bump Descriptions

Bump Name Pin Descriptions

A1 SW Regulator Switching Node

A2 VDD Power Supply

A3 OUTL Left Channel Output

A4 INL- Left Channel Inverting Input

B1 GND Ground

B2 C1P Charge Pump Flying Capacitor Positive Terminal

B3 HPVDD Amplifier Power Supply/Regulator Output

B4 INL+ Left Channel Non-Inverting Input

C1 C1N Charge Pump Flying Capacitor Negative Terminal

C2 HPVSS Charge Pump Output

C3 COM Common-mode Sense Input. Connect to headphone jack return

C4 INR+ Right Channel Non-Inverting Input

D1 SDA I2C Serial Data Input

D2 SCL I2C Serial Clock Input

D3 OUTR Right Channel Output

D4 INR- Right Channel Inverting Input

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LM48824

Absolute Maximum Ratings (Note 1, Note

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage (Note 1) 6V

Storage Temperature −65°C to +150°C

Input Voltage -0.3V to VDD + 0.3V

Power Dissipation (Note 3) Internally Limited

ESD Rating (Note 4) 2000V

ESD Rating (Note 5) 200V

ESD Rating (Note 6) 500V

Junction Temperature 150°C

Soldering Information

Vapor Phase (60 sec.)

215°C

Infrared (15 sec.) 220°C

Thermal Resistance

θJA (TMA16DDA) 60°C/W

Soldering Information

See AN-1112 “Micro SMD Wafer Level Chip Scale package”

Operating Ratings

Temperature Range

TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ +85°C

Supply Voltage (VDD) 2.4V ≤ VDD ≤ 5.5V

Electrical Characteristics VDD = 3.6V (Note 1, Note 2)

The following specifications apply for AV = 0dB, RL = 32Ω, f = 1kHz, unless otherwise specified. Limits apply to TA = 25°C.

Symbol Parameter Conditions

LM48824 Units

(Limits)

Typical

(Note 7)

Limit

(Note 8)

IDD Quiescent Power Supply Current

VIN = 0V, both channels active

RL = ∞0.9 1.3 mA (max)

RL = ∞, Low THD mode 1.55 mA

IDD(OP) Operating Power Supply Current

PO = 100µW, two channels in phase,

3dB Crest Factor, RL = 32Ω + 15Ω 1.8 2.5 mA (max)

PO = 100µW, two channels in phase,

3dB Crest Factor, RL = 32Ω + 15Ω,

Low THD mode

2.2 mA

PO = 500µW, two channels in phase,

3dB Crest Factor RL = 32Ω + 15Ω 3.1 3.8 mA (max)

PO = 500µW, two channels in phase,

3dB Crest Factor RL = 32Ω + 15Ω,

Low THD mode

3.4 mA

PO = 1mW, two channels in phase, 3dB

Crest Factor, RL = 32Ω + 15Ω 4.1 4.9 mA (max)

PO = 1mW, two channels in phase, 3dB

Crest Factor, RL = 32Ω + 15Ω,

Low THD mode

4.4 mA

ISD Shutdown Current Shutdown Enabled

VSCL = VSDA = 1.8V 2.5 3.9 µA (max)

VOS Output Offset Voltage VIN = 0V 0.15 0.65 mV (max)

TWU Wake Up Time From Shutdown 2 ms

AVGain

Minimum Gain Setting –59 –58

–60

dB (max)

dB (min)

Maximum Gain Setting 4 4.5

3.5

dB (max)

dB (min)

AV(MUTE) Mute Attenuation –110 dB

RIN Input Resistance AV = 4dB

AV = –59dB

kΩ (min)

kΩ (max)

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LM48824

Symbol Parameter Conditions

LM48824 Units

(Limits)

Typical

(Note 7)

Limit

(Note 8)

POOutput Power

f = 1kHz, THD+N = 1%

Two channels in phase

RL= 16Ω

37 30 mW (min)

f = 1kHz, THD+N = 1%

Two channels in phase

RL= 32Ω,

29 23 mW (min)

VOOutput Swing

THD+N = 1%, Two Channels in Phase

RL = 16Ω 0.77 0.7 VRMS

(min)

RL = 32Ω 0.96 0.86 VRMS

(min)

RL = 32Ω + 15Ω 1.05 VRMS

RL = 10kΩ1.3 1.1 VRMS

(min)

THD+N Total Harmonic Distortion + Noise

f = 1kHz, Single Channel

VO = 600mVRMS, RL = 16Ω 0.05 %

VO = 600mVRMS, RL = 16Ω,

Low THD Mode 0.03 %

VO = 800mVRMS, RL = 32Ω, 0.035 %

VO = 800mVRMS, RL = 32Ω,

Low THD Mode 0.02 %

VO = 900mVRMS, RL = 32Ω+ 15Ω 0.027 0.04 %(max)

VO = 900mVRMS, RL = 32Ω+ 15Ω,

Low THD Mode 0.015 %

PSRR Power Supply Rejection Ratio

VRIPPLE = 200mVP-P, Inputs AC GND

CIN = 1μF, input referred,

fRIPPLE = 217Hz 100 94 dB (min)

fRIPPLE = 1kHz 100 dB

CMRR Common Mode Rejection Ratio VRIPPLE = 1VP-P, fRIPPLE = 217Hz 60 dB

XTALK Crosstalk RL ≥ 16Ω, PO = 5mW, f = 1kHz 80 70 dB (min)

RL ≥ 10kΩ, VOUT = 1VRMS, f = 1kHz 110 95 dB (min)

SNR Signal-to-Noise Ratio

VOUT = 1VRMS, f = 1kHz 102 98 dB (min)

VOUT = 1VRMS, f = 1kHz,

Low THD Mode 105 dB

∈OS Output Noise

AV = 4dB, A-Weighted Filter 8 12 μV(max)

AV = 4dB, A-weighted Filter,

Low THD Mode 7 μV

ROUT Output Impedance

Charge pump-only mode enabled

f < 40kHz 43 30 kΩ (min)

f = 6MHz 500 Ω (min)

f = 36MHz 75 Ω (min)

CLMaximum Capacitive Load

No Sustained Oscillations

with 5Ω series resistance 100 nF

with no series resistance 100 pF

VOUT Maximum Voltage Swing Voltage applied to amplifier outputs in

charge pump-only mode 1.1 1.0 VRMS

(min)

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LM48824

I2C Interface Characteristics VDD = 3.6V (Note 1, Note 2)

The following specifications apply for AV = 0dB, RL = 16Ω, f = 1kHz, unless otherwise specified. Limits apply to TA = 25°C.

Symbol Parameter Conditions

LM48824 Units

(Limits)

Typical

(Note 7)

Limit

(Note 8)

t1SCL Period 2.5 μs (min)

t2SDA Setup Time 250 ns (min)

t3SDA Stable Time 250 ns (min)

t4Start Condition Time 250 ns (min)

t5Stop Condition Time 250 ns (min)

VIH Input High Voltage 1.2 V (min)

VIL Input Low Voltage 0.6 V (max)

Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability

and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in

the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the

device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified

Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified

or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed.

Note 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.

Note 4: Human body model, applicable std. JESD22-A114C.

Note 5: Machine model, applicable std. JESD22-A115-A.

Note 6: Charged Device Model, applicable std. JESD22-C101-C.

Note 7: Typical values represent most likely parametric norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product

characterization and are not guaranteed.

Note 8: Datasheet min/max specification limits are guaranteed by test or statistical analysis.

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LM48824

Typical Performance Characteristics

THD+N vs Frequency

VDD = 3.6V, RL = 16Ω, VO = 600VRMS

Low THD Mode

300892b9

THD+N vs Frequency

VDD = 3.6V, RL = 16Ω, VO = 600VRMS

300892c0

THD+N vs Frequency

VDD = 3.6V, RL = 32Ω, VO = 800VRMS

Low THD Mode

300892c1

THD+N vs Frequency

VDD = 3.6V, RL = 32Ω, VO = 800VRMS

300892c2

THD+N vs Frequency

VDD = 3.6V, RL = 47Ω, VO = 900VRMS

Low THD Mode

30089224

THD+N vs Frequency

VDD = 3.6V, RL = 47Ω, VO = 900VRMS

30089225

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LM48824

THD+N vs Output Voltage

VDD = 3.6V, RL = 16Ω, f = 1kHz

Low THD Mode

300892c5

THD+N vs Output Voltage

VDD = 3.6V, RL = 16Ω, f = 1kHz

300892c6

THD+N vs Output Voltage

VDD = 3.6V, RL = 32Ω, f = 1kHz

Low THD Mode

300892c7

THD+N vs Output Voltage

VDD = 3.6V, RL = 32Ω, f = 1kHz

300892c8

THD+N vs Output Voltage

VDD = 3.6V, RL = 47Ω, f = 1kHz

Low THD Mode

300892c9

THD+N vs Output Voltage

VDD = 3.6V, RL = 47Ω, f = 1kHz

300892d0

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LM48824

THD+N vs Output Power

VDD = 3.6V, RL = 16Ω, f = 1kHz

Low THD Mode

300892d1

THD+N vs Output Power

VDD = 3.6V, RL = 16Ω, f = 1kHz

300892d2

THD+N vs Output Power

VDD = 3.6V, RL = 32Ω, f = 1kHz

Low THD Mode

300892d3

THD+N vs Output Power

VDD = 3.6V, RL = 32Ω, f = 1kHz

300892d4

Power Dissipation vs Output Power

VDD = 3.6V, RL = 16Ω, f = 1kHz

300892d8

Power Dissipation vs Output Power

VDD = 3.6V, RL = 32Ω, f = 1kHz

300892d9

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LM48824

Power Dissipation vs Output Power

VDD = 3.6V, RL = 47Ω, f = 1kHz

300892e0

Output Power vs Supply Voltage

RL = 16Ω, f = 1kHz

300892e2

Output Power vs Supply Voltage

RL = 32Ω, f = 1kHz

300892e3

Output Power vs Supply Voltage

RL = 47Ω, f = 1kHz

300892e4

Supply Current vs Supply Voltage

No Load

300892e6

CMRR vs Frequency

VDD = 3.6V, VRIPPLE = 1VP-P

RL = 32Ω

300892h7

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LM48824

PSRR vs Frequency

VDD = 3.6V, VRIPPLE = 200VP-P

RL = 32Ω

300892h8

Crosstalk vs Frequency

VDD = 3.6V, PO = 5mW

RL = 32Ω

300892h9

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LM48824

Application Information

I2C COMPATIBLE INTERFACE

The LM48824 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 drain). The LM48824 and the master can

communicate at clock rates up to 400kHz. Figure 2 shows the

I2C interface timing diagram. Data on the SDA line must be

stable during the HIGH period of SCL. The LM48824 is a

transmit/receive slave-only device, reliant upon the master to

generate the SCL signal. Each transmission sequence is

framed by a START condition and a STOP condition (Figure

3). Each data word, device address and data, transmitted

over the bus is 8 bits long and is always followed by an ac-

knowledge pulse (Figure 4). The LM48824 device address is

1100000.

I2C BUS FORMAT

The I2C bus format is shown in Figure 4. The START signal,

the transition of SDA from HIGH to LOW while SCL is HIGH,

is generated, alerting all devices on the bus that a device ad-

dress is being written to the bus.

The 7-bit device address is written to the bus, most significant

bit (MSB) first, followed by the R/W bit (R/W = 0 indicates the

master is writing to the LM48824, R/W = 1 indicates the mas-

ter wants to read data from the LM48824). Data is latched into

the device on the rising clock edge. Each address bit must be

stable while SCL is HIGH. After the last address bit is trans-

mitted, the master device releases SDA, during which time,

an acknowledge clock pulse is generated by the slave device.

If the LM48824 receives the correct address, the device pulls

the SDA line low, generating an acknowledge bit (ACK).

Once the master device registers the ACK bit, the 8-bit reg-

ister address word is sent. Each data bit should be stable

while SCL is HIGH. After the 8-bit register address is sent, the

LM48824 sends another ACK bit. Following the acknowledg-

ment of the register address, the 8-bit register data word is

sent. Each data bit should be stable while SCL is HIGH. After

the 8-bit register data is sent, the LM48824 sends another

ACK bit. Following the acknowledgement of the register data

word, the master issues a STOP bit, allowing SDA to go high

while SCL is high.

30089201

FIGURE 2. I2C Timing Diagram

30089202

FIGURE 3. Start and Stop Diagram

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LM48824

30089214

FIGURE 4. I2C Write Cycle

30089269

FIGURE 5. Example I2C Read Cycle

TABLE 1. Device Address

B7 B6 B5 B4 B3 B2 B1 B0 (R/W)

Device

Address 1 1 0 0 0 0 0 X

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LM48824

TABLE 2. I2C Control Registers (Note 9)

Address

Name B7 B6 B5 B4 B3 B2 B1 B0

0x01h MODE

CONTROL HPL_EN HPR_EN 0 0 0 0 THRM SHDN

0x02h VOLUME

CONTROL MUTE_L* MUTE_R* VOL4 VOL3 VOL2 VOL1 VOL0 0

0x03h OUTPUT

CONTROL 0 0 0 0 LOW_THD 0 HiZ_L HiZ_R

0x04h

DEVICE

INFORMATI

ON (Read-

Only)

0 1 0 0 0 0 0 0

Note 9: * All registers default to 0 on initial power-up except SHDN, MUTE_L, MUTE_R bits default to 1 at power-up.

TABLE 3. Mode Control Register

Bit Name Value Description

B0 SHDN 0 Device enabled

1 Device disabled

B1 THRM

(Read Only)

0 Thermal-protection inactive

1 Thermal-protection active

B6 HPR_EN 0 Right channel amplifier disabled

1 Right channel amplifier enabled

B7 HPL_EN 0 Left channel amplifier disabled

1 Left channel amplifier enabled

TABLE 4. Volume Control Register

Bit Name Value Description

B5:B1 VOL4:VOL0

These bits set the volume level. See Table 5

(Volume Control).

B6 MUTE_R 0 Right Channel Mute Disabled

1 Right Channel Mute Enabled

B7 MUTE_L 0 Left Channel Mute Disabled

1 Left Channel Mute Enabled

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LM48824

TABLE 5. Volume Control

Volume Step VOL4 VOL3 VOL2 VOL1 VOL0 HP Gain (dB)

0 0 0 0 0 0 -59

1 0 0 0 0 1 -55

2 0 0 0 1 0 -51

3 0 0 0 1 1 -47

4 0 0 1 0 0 -43

5 0 0 1 0 1 -39

6 0 0 1 1 0 -35

7 0 0 1 1 1 -31

8 0 1 0 0 0 -27

9 0 1 0 0 1 -25

10 0 1 0 1 0 -23

11 0 1 0 1 1 -21

12 0 1 1 0 0 -19

13 0 1 1 0 1 -17

14 0 1 1 1 0 -15

15 0 1 1 1 1 -13

16 1 0 0 0 0 -11

17 1 0 0 0 1 -10

18 1 0 0 1 0 -9

19 1 0 0 1 1 -8

20 1 0 1 0 0 -7

21 1 0 1 0 1 -6

22 1 0 1 1 0 -5

23 1 0 1 1 1 -4

24 1 1 0 0 0 -3

25 1 1 0 0 1 -2

26 1 1 0 1 0 -1

27 1 1 0 1 1 0

28 1 1 1 0 0 1

29 1 1 1 0 1 2

30 1 1 1 1 0 3

31 1 1 1 1 1 4

TABLE 6. Output Control Register

Bit Name Value Description

B0 HiZ_R 0 Right channel high impedance mode disabled

1 Right channel high impedance mode enabled

B1 HiZ_L 0 Left channel high impedance mode disabled

1 Left channel high impedance mode enabled

B3 LOW_THD 0 LOW_THD mode disabled

1 LOW_THD mode enabled, improves overall THD

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LM48824

GENERAL DEVICE FUNCTION

The LM48824 integrates a high efficiency step down (buck)

DC-DC switching regulator with a ground reference head-

phone amplifier. The switching regulator delivers a constant

voltage from an input voltage ranging from 2.4V to 5.5V. The

switching regulator uses a voltage-mode architecture with

synchronous rectification, improving efficiency and reducing

component count.

The LM48824 headphone amplifier features National’s

ground referenced architecture that eliminates the large DC-

blocking capacitors required at the outputs of traditional sin-

gle-ended headphone amplifiers. A low-noise inverting

charge pump creates a negative supply (HPVSS) from the

positive supply voltage (VDD). The headphone amplifiers op-

erate from these bipolar supplies, with the amplifier outputs

biased about GND. Because there is no DC component on

the output signals, the large DC-blocking, AC coupling ca-

pacitors (typically 220µF) are not necessary, conserving

board space, reducing system cost, and improving frequency

response.

CLASS G OPERATION

Class G is a modification of some other class of amplifier

(normally Class B or Class AB) to increase efficiency and re-

duce power dissipation. Class G works off the fact that musi-

cal and voice signals have a high peak to mean ratio with most

of the signal content at low levels. To decrease power dissi-

pation, Class G has multiple voltage supplies. The LM48824

has two discrete voltage supplies at the output of the buck,

1.1V and 1.8V. When the output reached the threshold to

switch to the higher voltage rails, the rails will switch from 1.1V

to 1.8V. When the output falls below the required voltage rails

for a set period of time, it will switch back to the lower rail until

the next time the threshold is reached. Power dissipation is

greatly reduced for typical musical or voice sources. The

drawing below shows how a musical output may look. The

green lines are the supply voltages at the output of the buck

converter.

30089248

FIGURE 6. Class G Operation

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LM48824

DIFFERENTIAL AMPLIFIER EXPLANATION

The LM48824 features a differential input stage, which offers

improved noise rejection compared to a single-ended input

amplifier. Because a differential input amplifier amplifies the

difference between the two input signals, any component

common to both signals is cancelled.

SYNCHRONOUS RECTIFIER

The buck converter in the LM48824 uses an internal NFET

synchronous rectifier to reduce rectifier forward voltage drop

and associated power loss. Synchronous rectification pro-

vides a significant improvement in efficiency whenever the

output voltage is relative low compared to the voltage drop

across an ordinary rectifier diode and eliminating the need for

the diode.

CURRENT LIMITING

A current limit of the buck converter in the LM48824 allows

the device to protect itself and external components during

overload conditions.

PFM OPERATION

During PFM(Pulse-Frequency Modulation) operation, if the

output voltage of the buck converter is below the ‘high’ PFM

comparator threshold, the PMOS power switch is turned on.

It remains on until the output voltage reaches the ‘high’ PFM

threshold or the peak current exceeds the IPFM level set for

PFM mode. The typical peak current in PFM mode is IPFM =

112mA + VDD/27Ω.

Once the PMOS power switch is turned off, the NMOS power

switch is turned on until the inductor current ramps to zero.

When the NMOS zero-current condition is detected, the

NMOS power switch is turned off. If the output voltage is be-

low the ‘high’ PFM comparator threshold, the PMOS switch is

again turned on and the cycle is repeated until the output

reaches the desired level. Once the output reaches the ‘high’

PFM threshold, the NMOS switch is turned on briefly to ramp

the inductor current to zero and then both output switches are

turned off and the part enters an extremely low power mode.

30089205

FIGURE 7. PFM Operation

SOFT START

The buck converter has a soft-start circuit that limits in-rush

current during start-up. During start-up the switch current limit

is increased in steps. Soft start is activated only if global

SHDN goes from 1 to 0 after VDD reaches 2.7V. Soft start is

implemented by increasing switch current limit in steps of 70-

mA, 140mA, 280mA, and 750mA (typical switch current limit).

The start-up time thereby depends on the output capacitor

and load current of the buck converter. Typical start-up times

with a 10uF output capacitor and 150mA load is 280us and

with 5mA load is 240us.

COMMON-MODE SENSE

The LM48824 features a ground (common mode) sensing

feature. In noisy applications, or where the headphone jack is

used as a line out to other devices, noise pick up and ground

imbalance can degrade audio quality. The LM48824 COM in-

put senses and corrects any noise at the headphone return,

or any ground imbalance between the headphone return and

device ground, improving audio reproduction. Connect COM

directly to the headphone return terminal of the headphone

jack (Figure 8). No additional external components are re-

quired. Connect COM to GND if the common-mode sense

feature is not in use.

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LM48824

30089206

FIGURE 8. COM Connection

SHUTDOWN FUNCTION

The LM48824 features individual amplifier shutdown control

and a global device shutdown control.

Bit B0 (SHDN) of the MODE CONTROL register controls the

global shutdown for the entire device. Set SHDN = 1 to put

the device into current-saving shutdown mode, and set SHDN

= 0 for normal operation. SHDN defaults to 1 at power-up.

Bit B7 (HPL_EN) and Bit B6 (HPR_EN) of the MODE CON-

TROL register (register address 0x01h) controls the left and

right headphone amplifier shutdown respectively. Set

HPL_EN = 0 to set the left channel headphone amplifier to

shutdown and set HPL_EN = 1 to enable left channel opera-

tion. Set HPR_EN = 0 to set the right channel headphone

amplifier to shutdown and set HPR_EN = 1 to enable right

channel operation. The left and right channel amplifier shut-

downs operate individually.

The LM48824 has a shutdown time of 3ms to complete the

internal shutdown sequence. After SHDN is set to 1, any new

I2C commands should only be sent after the 3ms shutdown

time to ensure proper operation of the device.

MUTE FUNCTION

The LM48824 features independent left and right channel

mute functions.

Bit B7 (MUTE_L) and Bit B6 (MUTE_R) of the VOLUME

CONTROL register (register address 0x02h) controls the

mute function of the left and right channels respectively. Set

MUTE_L = 1 to mute the left channel and set the MUTE_R =

1 to mute the right channel. Set MUTE_L = 0 and MUTE_R =

0 to disable mute on the respective channels. MUTE_L and

MUTE_R defaults to 1 at power-up.

LOW THD+N MODE

The LM48824 features a Low THD mode that reduces THD

+N to improve audio qaulity. Set B3 (Low_THD) of the OUT-

PUT CONTROL register (register address 0x03h) to 1 to

enable the Low THD mode. There is a quiescent and operat-

ing current increase in Low THD mode. See Electrical Char-

acteristics table and Typical Performance Characteristics for

reference.

PROPER SELECTION OF EXTERNAL COMPONENTS

INDUCTOR SELECTION

There are two main considerations when choosing an induc-

tor; the inductor saturation current and the inductor current

ripple should be small enough to achieve the desired output

voltage ripple. Different saturation current rating specifica-

tions are followed by different manufacturers so attention

must be given to details. Saturation current ratings are typi-

cally specified at 25°C, ratings at the maximum ambient tem-

perature of application should be requested from the

manufacturer. Shielded capacitors are preferred since these

capacitors radiate less noise. Inductors with low DCR should

also be considered to minimize the efficiency.

Inductor value involves trade-offs in performance. Larger in-

ductors reduce inductor triple current, which typically means

less output voltage ripple (for a given size of output capacitor).

REGULATOR INPUT CAPACITOR SELECTION (C3)

A ceramic input capacitor of 1µF, 6.3V is sufficient for most

applications. Place the input capacitor as close as possible to

the VDD pin of the device. A larger value may be used for im-

proved input voltage filtering. Use X7R or X5R types; do not

use Y5V. DC bias characteristics of ceramic capacitors must

be considered when selecting case sizes like 0805 and 0603.

REGULATOR OUTPUT CAPACITOR SELECTION (C4)

A low ESR ceramic output capacitor of 10µF, 6.3V is sufficient

for most applications. Use X7R or X5R types; do not use Y5V.

DC bias characteristics of ceramic capacitors must be con-

sidered when selecting case sizes like 0805 and 0603. DC

bias characteristics vary from manufacturer to manufacturer

and dc bias curves should be requested from them as part of

the capacitor selection process.

CHARGE PUMP CAPACITOR SELECTION

Use low ESR ceramic capacitors (less than 100mΩ) for opti-

mum performance.

CHARGE PUMP FLYING CAPACITOR (C1)

The flying capacitor (C1) affects the load regulation and out-

put impedance of the charge pump. A C1 value that is too low

results in a loss of current drive, leading to a loss of amplifier

headroom. A higher valued C1 improves load regulation and

lowers charge pump output impedance to an extent. Above

2.2µF, the RDS(ON) of the charge pump switches and the ESR

of C1 and C2 dominate the output impedance. A lower value

capacitor can be used in systems with low maximum output

power requirements.

19 www.national.com

LM48824

CHARGE PUMP HOLD CAPACITOR (C2)

The value and ESR of the hold capacitor (C2) directly affects

the ripple on CPVSS. Increasing the value of C2 reduces out-

put ripple. Decreasing the ESR of C2 reduces both output

ripple and charge pump output impedance. A lower value ca-

pacitor can be used in systems with low maximum output

power requirements.

Amplifier Input Capacitor Selection

Input capacitors may be required for some applications, or

when the audio source is single-ended. Input capacitors block

the DC component of the audio signal, eliminating any conflict

between the DC component of the audio source and the bias

voltage of the LM48824. The input capacitors create a high-

pass filter with the input resistors RIN. The -3dB point of the

high-pass filter is found using Equation (1) below.

f = 1 / 2πRINCIN (Hz) (1)

Where the value of RIN is given in the Electrical Characteris-

tics Table.

High-pass filtering the audio signal can be beneficial for some

applications. When the LM48824 is using a single-ended

source, power supply noise on the ground is seen as an input

signal. Setting the high-pass filter point above the power sup-

ply noise frequencies, 217Hz in a GSM phone, for example,

filters out the noise such that it is not amplified and heard on

the output. Capacitors with a tolerance of 10% or better are

recommended for impedance matching and improved CMRR

and PSRR.

SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION

The LM48824 is compatible with single-ended sources. Fig-

ure 9 shows the typical single-ended applications circuit. Input

coupling capacitors are required for single-ended configura-

tion.

30089250

FIGURE 9. Single-Ended Input Configuration

www.national.com 20

LM48824

PCB LAYOUT CONFIGURATION

TABLE 7. LM48824TM Demoboard Bill of Materials

Designator Quantity Description

C1 1 10µF ±10% 16V 500Ω Tantalum Capacitor (B Case) AVX TPSB106K016R0500

C2 1 1μF ±10% 16V X5R Ceramic Capacitor (603) Panasonic ECJ-1VB1C105K

C3, C8, C9 3 2.2μF ±10% 10V X5R Ceramic Capacitor (603) Panasonic ECJ-1VB1A225K

C4 – C7 4 1μF ±10% 16V X7R Ceramic Capacitor (1206) Panasonic ECJ-3YB1C105K

R1, R2 2 5kΩ ±5% 1/10W Thick Film Resistor (603) Vishay CRCW06035R1KJNEA

L1 1 3.3μH ± 30% 1.2A Inductor Murata LQM2MPN3R3NG0L

J1 1 Stereo Headphone Jack

J2 1 16-Pin Boardmount Socket 3M 8516-4500JL

JU1 1 3 Pin Header

JU2 1 2 Pin Header

LM4822TM 1 LM48824TM (16-Bump microSMD)

21 www.national.com

LM48824

Demoboard Schematic

300892h6

FIGURE 10. LM48824 Demoboard Schematic

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LM48824

300892h5

FIGURE 11. Top Silkscreen

300892h1

FIGURE 12. Top Layer

23 www.national.com

LM48824

300892h2

FIGURE 13. Layer 2 (GND)

300892h3

FIGURE 14. Layer 3 (VDD)

www.national.com 24

LM48824

300892h4

FIGURE 15. Bottom Layer

300892h0

FIGURE 16. Bottom Silkscreen

25 www.national.com

LM48824

Revision History

Rev Date Description

1.0 08/06/09 Initial released of the full datasheet.

1.01 08/31/09 Text edits.

www.national.com 26

LM48824

Physical Dimensions inches (millimeters) unless otherwise noted

16 – Bump micro SMD

Order Number LM48824TM

NS Package Number TMD16DDA

X1 = 1690μm X2 = 1690μm X3 = 600μm

27 www.national.com

LM48824

Notes

LM48824 Class G Headphone Amplifier with I2C Volume Control

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