LM48310SDBD/NOPB - NATIONAL SEMICONDUCTOR

LM48310

LM48310 Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power

Amplifierwith E2S

Literature Number: SNAS430C

LM48310 June 24, 2008

Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio

Power Amplifier with E2S

General Description

The LM48310 is a single supply, high efficiency, mono, 2.6W,

filterless switching audio amplifier. The LM48310 features

National’s Enhanced Emissions Suppression (E2S) system,

that features a unique patent-pending ultra low EMI, spread

spectrum, PWM architecture, that significantly reduces RF

emissions while preserving audio quality and efficiency. The

E2S system improves battery life, reduces external compo-

nent count, board area consumption, system cost, and sim-

plifying design.

The LM48310 is designed to meet the demands of portable

multimedia devices. Operating from a single 5V supply, the

device is capable of delivering 2.6W of continuous output

power to a 4Ω load with less than 10% THD+N. Flexible power

supply requirements allow operation from 2.4V to 5.5V. The

LM48310 offers two logic selectable modulation schemes,

fixed frequency mode, and an EMI suppressing spread spec-

trum mode. The E2S system includes an advanced, patent-

pending edge rate control (ERC) architecture that further

reduce emissions by minimizing the high frequency compo-

nent of the device output, while maintaining high quality audio

reproduction (THD+N = 0.03%) and high efficiency (η = 88%).

The LM48310 also features a SYNC_IN input and

SYNC_OUT, which allows multiple devices to operate with

the same switching frequency, eliminating beat frequencies

and any other interference caused by clock intermodulation.

The LM48310 features high efficiency compared to conven-

tional Class AB amplifiers, and other low EMI Class D ampli-

fiers. When driving and 8Ω speaker from a 5V supply, the

device operates with 88% efficiency at PO = 1W. The gain of

the LM48310 is internally set to 12dB, further reducing exter-

nal component count. A low power shutdown mode reduces

supply current consumption to 0.01μA.

Advanced output short circuit protection with auto-recovery

prevents the device from being damaged during fault condi-

tions. Superior click and pop suppression eliminates audible

transients on power-up/down and during shutdown.

Key Specifications

■ Efficiency at 3.6V, 400mW into 8Ω85% (typ)

■ Efficiency at 5V, 1W into 8Ω88% (typ)

■ Quiescent Power Supply Current at 5V 3.2mA

■ Power Output at VDD = 5V,

RL = 4Ω, THD+N ≤ 10% 2.6W (typ)

■ Power Output at VDD = 5V,

RL = 8Ω, THD+N ≤ 10% 1.6W (typ)

■ Shutdown current 0.01μA (typ)

Features

■Passes FCC Class B Radiated Emissions with 20 inches

of cable

■E2S System Reduces EMI while Preserving Audio Quality

and Efficiency

■Output Short Circuit Protection with Auto-Recovery

■Stereo Class D operation

■No output filter required

■Internally Configured Gain (12dB)

■Synchronizable Oscillator for Multi-Channel operation

■Low power shutdown mode

■Minimum external components

■"Click and pop" suppression

■Micro-power shutdown

■Available in space-saving LLP package

Applications

■Mobile phones

■PDAs

■Laptops

EMI Graph 20in of Speaker Cable

300374a0

Boomer® is a registered trademark of National Semiconductor Corporation.

LM48310 Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S

Typical Application

30037459

FIGURE 1. Typical Audio Amplifier Application Circuit

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LM48310

Connection Diagram

LLP Package

3mm x 3mm x 0.8mm

30037458

Top View

Order Number LM48310SD

See NS Package Number SDA010

Pin Descriptions

TABLE 1.

Pin Name Description

1 IN+ Non-Inverting Input

2 IN- Inverting Input

3 VDD Power Supply

4 SD Active Low Shutdown Input. Connect to VDD for normal operation.

5 SYNC_IN

Mode Select and External Oscillator Input.

SYNC_IN = VDD: Spread spectrum mode with fS = 300kHz ± 30%

SYNC_IN = GND: Fixed frequency mode with fS = 300kHz

SYNC_IN = Clocked: fS = external clock frequency

6 SYNC_OUT Clock Output

7 OUTB Inverting Output

8 GND Ground

9 PVDD H-Bridge Power Supply

10 OUTA Non-Inverting Output

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LM48310

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 6.0V

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

Junction Temperature 150°C

Thermal Resistance

θJC 8.2°C/W

θJA 49.2°C/W

Operating Ratings (Notes 1, 2)

Temperature Range

TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ +85°C

Supply Voltage 2.4V ≤ VDD ≤ 5.5V

Electrical Characteristics VDD = PVDD = 5V (Notes 2, 8)

The following specifications apply for AV = 12dB, (RL = 8Ω, SYNC_IN = VDD (Spread Spectrum mode), f = 1kHz, unless otherwise

specified. Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM48310 Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

VOS Differential Output Offset Voltage VIN = 0 1 3 mV (max)

IDD Quiescent Power Supply Current

VIN = 0, RL = ∞

VDD = 3.6V 2.7 3.9 mA (max)

VIN = 0, RL = ∞

VDD = 5V 3.2 4.4 mA (max)

IDD Quiescent Power Supply Current VIN = 0, VDD = 3.6V 2.7 mA

VIN = 0, VDD = 5V 3.2 mA

ISD Shutdown Current VSD = GND 0.01 1.0 μA

VIH Logic Input High Voltage SD input, VDD = 3.6V 1.4 V (min)

VIL Logic Input Low Voltage SD input, VDD = 3.6V 0.4 V (max)

TWU Wake Up Time 7.5 ms

fSW Switching Frequency

SYNC_IN = VDD (Spread Spectrum) 300±30 kHz

SYNC_IN = GND (Fixed Frequency) 300 kHz

SYNC_IN = External Clock

Minimum Frequency 200 kHz

SYNC_IN = External Clock

Maximum Frequency 1000 kHz

AVGain 12 11

dB (min)

dB (max)

RIN Input Resistance 20 17 kΩ (min)

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LM48310

Symbol Parameter Conditions

LM48310 Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

POOutput Power

RL = 4Ω, THD = 10%

f = 1kHz, 22kHz BW

VDD = 5V

VDD = 3.6V

VDD = 2.5V

2.6

1.3

555

RL = 8Ω, THD = 10% (max)

f = 1kHz, 22kHz BW

VDD = 5V

VDD = 3.6V

VDD = 2.5V

1.6

800

354

RL = 4Ω, THD = 1% (max)

f = 1kHz, 22kHz BW

VDD = 5V

VDD = 3.6V

VDD = 2.5V

2.1

446

RL = 8Ω, THD = 1% (max)

f = 1kHz, 22kHz BW

VDD = 5V

VDD = 3.6V

VDD = 2.5V

1.3

640

286

1.1 W (min)

THD+N Total Harmonic Distortion + Noise PO = 200mW, RL = 8Ω, f = 1kHz 0.03 % (max)

PO = 100mW, RL = 8Ω, f = 1kHz 0.03 %

PSRR Power Supply Rejection Ratio

(Input Referred)

VRIPPLE = 200mVP-P Sine,

fRIPPLE = 217Hz, Inputs AC GND,

CIN = 1μF, Input referred

VRIPPLE = 200mVP-P Sine,

fRIPPLE = 1kHz, Inputs AC GND,

CIN = 1μF, Input referred

CMRR Common Mode Rejection Ratio VRIPPLE = 1VP-P

fRIPPLE = 217Hz 70 dB

ηEfficiency

VDD = 5V, POUT = 1W

RL = 8Ω, f = 1kHz 88 %

VDD = 3.6V, POUT = 400mW

RL = 8Ω, f = 1kHz 85 %

SNR Signal to Noise Ratio

VDD = 5V, PO = 1W,

Fixed Frequency Mode 97 dB

VDD = 5V, PO = 1W,

Spread Spectrum Mode 97 dB

εOS Output Noise

Input referred,

Fixed Frequency Mode,

A-weighted Filter

μV

Input referred,

Spread Spectrum Mode,

Unweighted

μV

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LM48310

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 Conditionsindicate 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: 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 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis.

Note 8: RL is a resistive load in series with two inductors to simulate an actual speaker load. For RL = 8Ω, the load is 15µH + 8Ω, +15µH. For RL = 4Ω, the load

is 15µH + 4Ω + 15µH.

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LM48310

Typical Performance Characteristics

THD+N vs Frequency

VDD = 2.5V, POUT = 300mW, RL = 4Ω

30037466

THD+N vs Frequency

VDD = 3.6V, POUT = 700mW, RL = 4Ω

30037467

THD+N vs Frequency

VDD = 5.0V, POUT = 1.2W, RL = 4Ω

30037468

THD+N vs Frequency

VDD = 2.5V, POUT = 150mW, RL = 8Ω

30037469

THD+N vs Frequency

VDD = 3.6V, POUT = 400mW, RL = 8Ω

30037470

THD+N vs Frequency

VDD = 5V, POUT = 650mW, RL = 8Ω

30037471

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LM48310

THD+N vs Output Power

f = 1kHz, RL = 4Ω

30037464

THD+N vs Output Power

f = 1kHz, RL = 8Ω

30037465

Efficiency vs Output Power

f = 1kHz, RL = 4Ω

30037472

Efficiency vs Output Power

f = 1kHz, RL = 8Ω

30037473

Power Dissipation vs Output Power

f = 1kHz, RL = 4Ω

30037474

Power Dissipation vs Output Power

f = 1kHz, RL = 8Ω

30037475

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LM48310

Output Power vs Supply Voltage

f = 1kHz, RL = 4Ω

30037476

Output Power vs Supply Voltage

f = 1kHz, RL = 8Ω

30037477

PSRR vs Frequency

VDD = 3.6V, VRIPPLE = 200mVP-P, RL = 8Ω

30037497

PSRR vs Frequency

VDD = 5.0V, VRIPPLE = 200mVP-P, RL = 8Ω

30037498

CMRR vs Frequency

VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω

30037480

CMRR vs Frequency

VDD = 5.0V, VRIPPLE = 1VP-P, RL = 8Ω

30037463

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LM48310

Fixed Frequency Output Spectrum vs Frequency

VDD = 5.0V, VIN = 1VRMS, RL = 8Ω

30037482

Spread Spectrum Output Spectrum vs Frequency

VDD = 5.0V, VIN = 1VRMS, RL = 8Ω

30037483

Wideband Fixed Frequency Output Spectrum

vs Frequency

VDD = 5.0V, RL = 8Ω

30037484

Wideband Spread Spectrum Output Spectrum

vs Frequency

VDD = 5.0V, RL = 8Ω

30037485

Supply Current vs Supply Voltage

No Load

30037486

Shutdown Supply Current vs Supply Voltage

No Load

30037499

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LM48310

Application Information

GENERAL AMPLIFIER FUNCTION

The LM48310 mono Class D audio power amplifier features

a filterless modulation scheme that reduces external compo-

nent count, conserving board space and reducing system

cost. With no signal applied, the outputs (VOUTA and VOUTB)

switch between VDD and GND with a 50% duty cycle, in

phase, causing the two outputs to cancel. This cancellation

results in no net voltage across the speaker, thus there is no

current to the load in the idle state.

With the input signal applied, the duty cycle (pulse width) of

the LM48310 outputs changes. For increasing output voltage,

the duty cycle of VOUTAincreases, while the duty cycle of

VOUTB decreases. For decreasing output voltages, the con-

verse occurs. The difference between the two pulse widths

yields the differential output voltage.

ENHANCED EMISSIONS SUPPRESSION SYSTEM (E2S)

The LM48310 features National’s patent-pending E2S system

that reduces EMI, while maintaining high quality audio repro-

duction and efficiency. The E2S system features a synchro-

nizable oscillator with selectable spread spectrum, and

advanced edge rate control (ERC). The LM48310 ERC great-

ly reduces the high frequency components of the output

square waves by controlling the output rise and fall times,

slowing the transitions to reduce RF emissions, while maxi-

mizing THD+N and efficiency performance. The overall result

of the E2S system is a filterless Class D amplifier that passes

FCC Class B radiated emissions standards with 20in of twist-

ed pair cable, with excellent 0.03% THD+N and high 88%

efficiency.

FIXED FREQUENCY MODE (SYNC_IN = GND)

The LM48310 features two modulations schemes, a fixed fre-

quency mode and a spread spectrum mode. Select the fixed

frequency mode by setting SYNC_IN = GND. In fixed fre-

quency mode, the amplifier output switch at a constant

300kHz. In fixed frequency mode, the output spectrum con-

sists of the fundamental and its associated harmonics (see

Typical Performance Characteristics).

SPREAD SPECTRUM MODE (SYNC_IN = VDD)

The logic selectable spread spectrum mode eliminates the

need for output filters, ferrite beads or chokes. In spread

spectrum mode, the switching frequency varies randomly by

30% about a 300kHz center frequency, reducing the wide-

band spectral contend, improving EMI emissions radiated by

the speaker and associated cables and traces. Where a fixed

frequency class D exhibits large amounts of spectral energy

at multiples of the switching frequency, the spread spectrum

architecture of the LM48310 spreads that energy over a larger

bandwidth (See Typical Performance Characteristics). The

cycle-to-cycle variation of the switching period does not affect

the audio reproduction, efficiency, or PSRR. Set SYNC_IN =

VDD for spread spectrum mode.

EXTERNAL CLOCK MODE (SYNC_IN = CLOCK)

Connecting a clock signal to SYNC_IN synchronizes the

LM48310 oscillator to an external clock, moving the output

spectral components out of a sensitive frequency band, and

minimizing audible beat frequencies when multiple LM48310s

are used in a single system. The LM48310 accepts an exter-

nal clock frequency between 200kHz and 1MHz. The

LM48310 can be synchronized to a spread spectrum clock,

allowing multiple LM48310s to be synchronized in spread

spectrum mode (see SYNC_OUT section).

SYNC_OUT

SYNC_OUT is a clock output for synchronizing external de-

vices. The SYNC_OUT signal is identical in frequency and

duty cycle of the amplifier’s switching frequency. When the

LM48310 is in fixed frequency mode, SYNC_OUT is a fixed,

300kHz clock. When the LM48310 is in spread spectrum

mode, SYNC_OUT is an identical spread spectrum clock.

When the LM48310 is driven by an external clock,

SYNC_OUT is identical to the external clock. If unused, leave

SYNC_OUT floating.

Multiple LM48310s can be synchronized to a single clock. In

Figure 2, device U1 is the master, providing a spread spec-

trum clock to the slave device (U2). This configuration syn-

chronizes the switching frequencies of the two devices,

eliminating any audible beat frequencies. Because

SYNC_OUT has no audio content, there is minimal THD+N

degredation or crosstalk between the devices, Figure 3-5.

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LM48310

30037460

FIGURE 2. Cascaded LM48310

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LM48310

300374a1

FIGURE 3. THD+N vs Output Power

30037438

FIGURE 4. THD+N vs Frequency

30037496

FIGURE 5. Crosstalk vs Frequency

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LM48310

DIFFERENTIAL AMPLIFIER EXPLANATION

As logic supplies continue to shrink, system designers are in-

creasingly turning to differential analog signal handling to

preserve signal to noise ratios with restricted voltage signs.

The LM48310 features a fully differential speaker amplifier. A

differential amplifier amplifies the difference between the two

input signals. Traditional audio power amplifiers have typical-

ly offered only single-ended inputs resulting in a 6dB reduc-

tion of SNR relative to differential inputs. The LM48310 also

offers the possibility of DC input coupling which eliminates the

input coupling capacitors. A major benefit of the fully differ-

ential amplifier is the improved common mode rejection ratio

(CMRR) over single ended input amplifiers. The increased

CMRR of the differential amplifier reduces sensitivity to

ground offset related noise injection, especially important in

noisy systems.

POWER DISSIPATION AND EFFICIENCY

The major benefit of a Class D amplifier is increased efficiency

versus a Class AB. The efficiency of the LM48310 is attributed

to the region of operation of the transistors in the output stage.

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, along with switching losses due to gate charge.

SHUTDOWN FUNCTION

The LM48310 features a low current shutdown mode. Set

SD = GND to disable the amplifier and reduce supply current

to 0.01µA.

Switch SD between GND and VDD for minimum current con-

sumption is shutdown. The LM48310 may be disabled with

shutdown voltages in between GND and VDD, the idle current

will be greater than the typical 0.1µA value.

The LM48310 shutdown input has and internal pulldown re-

sistor. The purpose of this resistor is to eliminate any unwant-

ed state changes when SD is floating. To minimize shutdown

current, SD should be driven to GND or left floating. If SD is

not driven to GND or floating, an increase in shutdown supply

current will be noticed.

AUDIO AMPLIFIER POWER SUPPLY BYPASSING/

FILTERING

Proper power supply bypassing is critical for low noise per-

formance and high PSRR. Place the supply bypass capaci-

tors as close to the device as possible. Typical applications

employ a voltage regulator with 10µF and 0.1µF bypass ca-

pacitors that increase supply stability. These capacitors do

not eliminate the need for bypassing of the LM48310 supply

pins. A 1µF capacitor is recommended.

AUDIO 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 LM48310. 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

Where RIN is the value of the input resistor given in the Elec-

trical Characteristics table.

The input capacitors can also be used to remove low fre-

quency content from the audio signal. Small speakers cannot

reproduce, and may even be damaged by low frequencies.

High pass filtering the audio signal helps protect the speakers.

When the LM48310 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 supply noise fre-

quencies, 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 recommend-

ed for impedance matching and improved CMRR and PSRR.

AUDIO AMPLIFIER GAIN

The gain of the LM48310 is internally set to 12dB. The gain

can be reduced by adding additional input resistance (Figure

6). In this configuration, the gain of the device is given by:

AV = 2 x [RF / (RINEXT + RIN)]

Where RF is 40kΩ, RIN is 20kΩ, and RINEXT is the value of the

additional external resistor.

30037461

FIGURE 6. Reduced Gain Configuration

SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION

The LM48310 is compatible with single-ended sources. When

configured for single-ended inputs, input capacitors must be

used to block and DC component at the input of the device.

Figure 7 shows the typical single-ended applications circuit.

30037462

FIGURE 7. Single-Ended Input Configuration

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LM48310

PCB LAYOUT GUIDELINES

As output power increases, interconnect resistance (PCB

traces and wires) between the amplifier, load and power sup-

ply create a voltage drop. The voltage loss due to the traces

between the LM48310 and the load results in lower output

power and decreased efficiency. Higher trace resistance be-

tween the supply and the LM48310 has the same effect as a

poorly regulated supply, increasing ripple on the supply line,

and reducing peak output power. The effects of residual trace

resistance increases as output current increases due to high-

er output power, decreased load impedance or both. To main-

tain the highest output voltage swing and corresponding peak

output power, the PCB traces that connect the output pins to

the load and the supply pins to the power supply should be

as wide as possible to minimize trace resistance.

The use of power and ground planes will give the best THD

+N performance. In addition to reducing trace resistance, the

use of power planes creates parasitic capacitors that help to

filter the power supply line.

The inductive nature of the transducer load can also result in

overshoot on one of both edges, clamped by the parasitic

diodes to GND and VDD in each case. From an EMI stand-

point, this is an aggressive waveform that can radiate or

conduct to other components in the system and cause inter-

ference. In is essential to keep the power and output traces

short and well shielded if possible. Use of ground planes

beads and micros-strip layout techniques are all useful in pre-

venting unwanted interference.

As the distance from the LM48310 and the speaker increases,

the amount of EMI radiation increases due to the output wires

or traces acting as antennas become more efficient with

length. Ferrite chip inductors places close to the LM48310

outputs may be needed to reduce EMI radiation.

Designator Quantity Description

C1 1 10μF ±10% 16V 500Ω Tantalum

Capacitor (B Case) AVX

TPSB106K016R0500

C2, C3 2 1μF ±10% 16V X7R Ceramic

Capacitor (603) Panasonic

ECJ-1VB1C105K

C4, C5 2 1μF ±10% 16V X7R Ceramic

Capacitor (1206) Panasonic

ECJ-3YB1C105K

C6 1 Not Installed Ceramic Capacitor

(603)

R1 1 0Ω ±1% resistor (603)

JP1 — JP2 2 3 Pin Headers

LM48310SDL 1 LM48310SD (10-pin LLP)

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LM48310

LM48310 Demo Board Schematic

30037489

FIGURE 8. LM48310 DEMO BOARD SCHEMATIC

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LM48310

Demo Boards

30037490

FIGURE 9. Top Silkscreen

30037491

FIGURE 10. Top Layer

30037492

FIGURE 11. Layer 2 (GND)

30037493

FIGURE 12. Layer 3 (VDD )

30037494

FIGURE 13. Bottom Layer 30037495

FIGURE 14. Bottom Silkscreen

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LM48310

Revision History

Rev Date Description

1.0 11/13/07 Initial release.

1.01 02/26/08 Fixed few typos (Pin Description table).

1.02 03/04/08 Text edits under SHUTDOWN FUNCTION (Application Information section).

1.03 06/24/09 Text edits.

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LM48310

Physical Dimensions inches (millimeters) unless otherwise noted

LLP

Order Number LM48310SD

NS Package Number SDA08A

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LM48310

Notes

LM48310 Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S

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