LM4804LQ/NOPB - NATIONAL SEMICONDUCTOR

LM4804

LM4804 Low Voltage High Power Audio Power Amplifier

Literature Number: SNAS268B

LM4804

Low Voltage High Power Audio Power Amplifier

General Description

The LM4804 integrates a Boost Converter with an Audio

Power Amplifier to drive voice coil speakers in portable

applications. When powered by a 3V supply, it is capable of

creating 1.8W power dissipation in an 8Ωbridge-tied-load

(BTL) with less than 1% THD+N.

Boomer audio power amplifiers were designed specifically to

provide high quality output power with a minimal amount of

external components. The LM4804 does not require boot-

strap capacitors, or snubber circuits. Therefore it is ideally

suited for portable applications requiring high output voltage

and minimal size.

The LM4804 features a micro-power shutdown mode. Addi-

tionally, the LM4804 features an internal thermal shutdown

protection mechanism.

The LM4804 contains advanced pop & click circuitry that

eliminates output transients which would otherwise occur

during power or shutdown cycles.

The LM4804 is unity-gain stable. Its closed-loop gain is

determined by the value of external, user selected resistors.

Key Specifications

jQuiescent Power Supply Current

= 4.2V, R

=8Ω) 11mA (typ)

jBTL Output Power

=8Ω, 2% THD+N, V

= 3V) 1.8W (typ)

jShutdown Current 2µA (max)

Features

nPop & click circuitry eliminates noise during turn-on and

turn-off transitions

nLow, 2µA (max) shutdown current

nLow, 11mA (typ) quiescent current (V

= 4.2V, R

8Ω)

n1.8W mono BTL output, R

=8Ω,V

=3V

nShort circuit protection

nUnity-gain stable

nExternal gain configuration capability

Applications

nCellphone

nPDA

Connection Diagrams

LM4804LQ (5x5) LQ Marking

20116784

Top View

Order Number LM4804LQ

See NS Package Number LQA28A

20116737

Top View

U = Wafer Fab Code

Z = Assembly Plant Code

XY = Date Code

TT = Die Run Code

Boomer®is a registered trademark of National Semiconductor Corporation.

June 2005

LM4804 Low Voltage High Power Audio Power Amplifier

Typical Application

20116714

FIGURE 1. Typical LM4804 Audio Amplifier Application Circuit

LM4804

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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 (V

) 6.5V

Supply Voltage (V

) 6.5V

Storage Temperature −65˚C to +150˚C

Input Voltage −0.3V to V

+ 0.3V

Power Dissipation (Note 3) Internally limited

ESD Susceptibility (Note 4) 2000V

ESD Susceptibility (Note 5) 200V

Junction Temperature 125˚C

Thermal Resistance

(LLP) 59˚C/W

See AN-1187 ’Leadless Leadframe Packaging (LLP).’

Operating Ratings

Temperature Range

MIN

≤T

MAX

−40˚C ≤T

≤+85˚C

Supply Voltage (V

)3V≤V

≤5V

Supply Voltage (V

) 2.7V ≤V

≤6.1V

Electrical Characteristics V

= 4.2V (Notes 1, 2)

The following specifications apply for V

= 4.2V, V

= 6.0V, A

V-BTL

= 20dB, R

=8Ω,f

= 1kHz, C

= 1.0µF, R

= 301kΩ,R

= 78.7kΩunless otherwise specified. Limits apply for T

= 25˚C. See Figure 1.

Symbol Parameter Conditions LM4804 Units

(Limits)

Typical

(Note 6)

Limit

(Notes 7, 8)

Quiescent Power Supply Current V

=0,R

LOAD

=∞11 22 mA (max)

Shutdown Current V

SHUTDOWN

= GND (Notes 9, 10) 0.1 2 µA (max)

SDIH

Shutdown Voltage Input High SD1

SD2

0.7V

1.4 V (min)

SDIL

Shutdown Voltage Input Low SD1

SD2

0.15V

0.4 V (max)

Wake-up Time C

= 1.0µF 70 msec

(max)

Output Offset Voltage 4 40 mV (max)

TSD Thermal Shutdown Temperature 125 ˚C (min)

OUT

Output Power THD = 2% (max) 1.9 1.7 W (min)

THD+N Total Harmomic Distortion + Noise P

OUT

= 1.5W 0.13 0.5 %

Output Noise A-Weighted Filter, V

= 0V,

Input Referred

22 µV

PSRR Power Supply Rejection Ratio V

RIPPLE

= 200mV

p-p

f = 217Hz

f = 1kHz

dB (min)

Feedback Pin Reference Voltage 1.24 1.2772

1.2028

V (max)

V (min)

Electrical Characteristics V

= 3.0V (Notes 1, 2)

The following specifications apply for V

= 3.0V, V

= 6.0V, A

V-BTL

= 20dB, R

=8Ω,f

= 1kHz, C

= 1.0µF, R

= 301kΩ,R

= 78.7kΩunless otherwise specified. Limits apply for T

= 25˚C.

Symbol Parameter Conditions LM4804 Units

(Limits)

Typical

(Note 6)

Limit

(Notes 7, 8)

Quiescent Power Supply Current V

= 3.2V, V

=0,R

LOAD

=∞19 33 mA (max)

Shutdown Current V

SHUTDOWN

= GND (Notes 9, 10) 0.1 2 µA (max)

SDIH

Shutdown Voltage Input High SD1

SD2

0.7V

1.4 V (min)

SDIL

Shutdown Voltage Input Low SD1

SD2

0.15V

0.4 V (max)

Wake-up Time C

= 1.0µF 70 msec

(max)

Output Offset Voltage 3 40 mV (max)

LM4804

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Electrical Characteristics V

= 3.0V (Notes 1, 2) (Continued)

The following specifications apply for V

= 3.0V, V

= 6.0V, A

V-BTL

= 20dB, R

=8Ω,f

= 1kHz, C

= 1.0µF, R

= 301kΩ,R

= 78.7kΩunless otherwise specified. Limits apply for T

= 25˚C.

Symbol Parameter Conditions LM4804 Units

(Limits)

Typical

(Note 6)

Limit

(Notes 7, 8)

TSD Thermal Shutdown Temperature 125 ˚C (min))

OUT

Output Power THD = 2% (max) 1.8 1.65 W (min)

THD+N Total Harmomic Distortion + Noise P

OUT

= 1.5W 0.15 0.5 %

Output Noise A-Weighted Filter, V

= 0V,

Input Referred

30 µV

PSRR Power Supply Rejection Ratio V

RIPPLE

= 200mV

p-p

f = 217Hz

f = 1kHz

dB (min)

Feedback Pin Reference Voltage (Note 11) 1.24 1.2772

1.2028

V (max)

V (min)

Note 1: All voltages are measured with respect to the GND pin, unless otherwise specified.

Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions 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 TJMAX,θJA, and the ambient temperature, TA. The maximum

allowable power dissipation is PDMAX =(T

JMAX −T

A)/θJA or the given in Absolute Maximum Ratings, whichever is lower.

Note 4: Human body model, 100pF discharged through a 1.5kΩresistor.

Note 5: Machine Model, 220pF – 240pF discharged through all pins.

Note 6: Typicals are measured at 25˚C and represent the parametric norm.

Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

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

Note 9: Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to Vin for minimum shutdown

current.

Note 10: Shutdown current is measured with components R1 and R2 removed.

Note 11: Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is unloaded).

LM4804

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Typical Performance Characteristics

THD+N vs Frequency

= 4.2V, R

=8Ω,P

OUT

= 1.5W

THD+N vs Frequency

= 3.0V, R

=8Ω,P

OUT

= 1.5W

20116723 20116724

THD+N vs Output Power

= 4.2V, R

=8Ω, f = 1kHz

THD+N vs Output Power

= 3.0V, R

=8Ω

20116721 20116722

PSRR vs Frequency

= 3V, Input Referred

PSRR vs Frequency

= 4.2V, Input Referred

20116725 20116726

LM4804

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Typical Performance Characteristics (Continued)

Power Supply Current

vs Power Supply Voltage

=8Ω

Power Supply Current

vs Output Power

20116727 20116728

Output Power

vs Power Supply Voltage

=8Ω

Amplifier Circuit Dissipation

vs Load Dissipation

20116729 20116730

Efficiency vs V

OUT

= 5.0V

vs Temperature

20116731 20116732

LM4804

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Typical Performance Characteristics (Continued)

Frequency vs V

Maximum Start Up Voltage

vs Temperature

20116733 20116734

Typical R

DS(ON)

vs Temperature

Typical Current Limit

vs Temperature

20116735 20116736

LM4804

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Application Information

BRIDGE CONFIGURATION EXPLANATION

Audio Amplifier portion of the LM4804 has two operational

amplifiers internally, allowing for a few different amplifier

configurations. The first amplifier’s gain is externally config-

urable, while the second amplifier is internally fixed in a

unity-gain, inverting configuration. The closed-loop gain of

the first amplifier is set by selecting the ratio of Rf to Ri while

the second amplifier’s gain is fixed by the two internal 20kΩ

resistors. Figure 1 shows that the output of amplifier one

serves as the input to amplifier two which results in both

amplifiers producing signals identical in magnitude, but out

of phase by 180˚. Consequently, the differential gain for the

IC is

= 2 *(Rf/Ri)

By driving the load differentially through outputs Vo1 and

Vo2, an amplifier configuration commonly referred to as

“bridged mode” is established. Bridged mode operation is

different from the classical single-ended amplifier configura-

tion where one side of the load is connected to ground.

A bridge amplifier design has a few distinct advantages over

the single-ended configuration, as it provides differential

drive to the load, thus doubling output swing for a specified

supply voltage. Four times the output power is possible as

compared to a single-ended amplifier under the same con-

ditions. This increase in attainable output power assumes

that the amplifier is not current limited or clipped. In order to

choose an amplifier’s closed-loop gain without causing ex-

cessive clipping, please refer to the Audio Power Amplifier

Design section.

A bridge configuration also creates a second advantage over

single-ended amplifiers. Since the differential outputs, Vo1

and Vo2, are biased at half-supply, no net DC voltage exists

across the load. This eliminates the need for an output

coupling capacitor which is required in a single supply,

single-ended amplifier configuration. Without an output cou-

pling capacitor, the half-supply bias across the load would

result in both increased internal IC power dissipation and

also possible loudspeaker damage.

AMPLIFIER POWER DISSIPATION

Power dissipation is a major concern when designing a

successful amplifier, whether the amplifier is bridged or

single-ended. A direct consequence of the increased power

delivered to the load by a bridge amplifier is an increase in

internal power dissipation. Since the amplifier portion of the

LM4804 has two operational amplifiers, the maximum inter-

nal power dissipation is 4 times that of a single-ended am-

plifier. The maximum power dissipation for a given BTL

application can be derived from Equation 1.

DMAX(AMP)

= 4(V

)

/(2π

) (1)

BOOST CONVERTER POWER DISSIPATION

At higher duty cycles, the increased ON time of the FET

means the maximum output current will be determined by

power dissipation within the LM2731 FET switch. The switch

power dissipation from ON-state conduction is calculated by

Equation 2.

DMAX(SWITCH)

=DCxI

IND

(AVE)

(ON) (2)

There will be some switching losses as well, so some derat-

ing needs to be applied when calculating IC power dissipa-

tion.

TOTAL POWER DISSIPATION

The total power dissipation for the LM4804 can be calculated

by adding Equation 1 and Equation 2 together to establish

Equation 3:

DMAX(TOTAL)

= [4*(V

)

2π

]+[DCxI

IND

(AVE)

(ON)] (3)

The result from Equation 3 must not be greater than the

power dissipation that results from Equation 4:

DMAX

=(T

JMAX

-T

)/θJA (4)

For package LQA28A, θ

= 59˚C/W. T

JMAX

= 125˚C for the

LM4804. Depending on the ambient temperature, T

,ofthe

system surroundings, Equation 4 can be used to find the

maximum internal power dissipation supported by the IC

packaging. If the result of Equation 3 is greater than that of

Equation 4, then either the supply voltage must be in-

creased, the load impedance increased or T

reduced. For

the typical application of a 3V power supply, with V1 set to

6.0V and 8Ωload, the maximum ambient temperature pos-

sible without violating the maximum junction temperature is

approximately TBD˚C provided that device operation is

around the maximum power dissipation point. Thus, for typi-

cal applications, power dissipation is not an issue. Power

dissipation is a function of output power and thus, if typical

operation is not around the maximum power dissipation

point, the ambient temperature may be increased accord-

ingly. Refer to the Typical Performance Characteristics

curves for power dissipation information for lower output

levels.

EXPOSED-DAP PACKAGE PCB MOUNTING

CONSIDERATIONS

The LM4804’s exposed-DAP (die attach paddle) package

(LD) provides a low thermal resistance between the die and

the PCB to which the part is mounted and soldered. This

allows rapid heat transfer from the die to the surrounding

PCB copper traces, ground plane, and surrounding air. The

LD package should have its DAP soldered to a copper pad

on the PCB. The DAP’s PCB copper pad may be connected

to a large plane of continuous unbroken copper. This plane

forms a thermal mass, heat sink, and radiation area. Further

detailed and specific information concerning PCB layout,

fabrication, and mounting an LD (LLP) package is available

from National Semiconductor’s Package Engineering Group

under application note AN1187.

SHUTDOWN FUNCTION

In many applications, a microcontroller or microprocessor

output is used to control the shutdown circuitry to provide a

quick, smooth transition into shutdown. Another solution is to

use a single-pole, single-throw switch, in conjunction with an

external pull-up resistor to drive both shutdown pins simul-

taneously. When the switch is closed, the shutdown pin is

connected to ground which disables the amplifier. If the

switch is open, then the external pull-up resistor to V

will

enable the LM4804. This scheme guarantees that the shut-

down pins will not float thus preventing unwanted state

changes.

LM4804

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Application Information (Continued)

EXTERNAL COMPONENT SELECTION

Proper selection of external components in applications us-

ing integrated power amplifiers, and switching DC-DC con-

verters, is critical to optimize device and system perfor-

mance. Consideration to component values must be used to

maximize overall system quality.

The best capacitors for use with the switching converter

portion of the LM4804 are multi-layer ceramic capacitors.

They have the lowest ESR (equivalent series resistance)

and highest resonance frequency which makes them opti-

mum for use with high frequency switching converters.

When selecting a ceramic capacitor, only X5R and X7R

dielectric types should be used. Other types such as Z5U

and Y5F have such severe loss of capacitance due to effects

of temperature variation and applied voltage, they may pro-

vide as little as 20% of rated capacitance in many typical

applications. Always consult capacitor manufacturer’s data

curves before selecting a capacitor. High-quality ceramic

capacitors can be obtained from Taiyo-Yuden, AVX, and

Murata.

POWER SUPPLY BYPASSING

As with any amplifier, proper supply bypassing is critical for

low noise performance and high power supply rejection. The

capacitor location on both the bypass and power supply pins

should be as close to the device as possible.

SELECTING THE AUDIO AMPLIFIER’S INPUT

CAPACITOR

One of the major considerations is the closedloop bandwidth

of the amplifier. To a large extent, the bandwidth is dictated

by the choice of external components shown in Figure 1. The

input coupling capacitor, C

, forms a first order high pass filter

which limits low frequency response. This value should be

chosen based on needed frequency response for a few

distinct reasons.

Large input capacitors are both expensive and space hungry

for portable designs. Clearly, a certain sized capacitor is

needed to couple in low frequencies without severe attenu-

ation. But ceramic speakers used in portable systems,

whether internal or external, have little ability to reproduce

signals below 100Hz to 150Hz. Thus, using a large input

capacitor may not increase actual system performance.

In addition to system cost and size, click and pop perfor-

mance is effected by the size of the input coupling capacitor,

. A larger input coupling capacitor requires more charge to

reach its quiescent DC voltage (nominally 1/2 V

). This

charge comes from the output via the feedback and is apt to

create pops upon device enable. Thus, by minimizing the

capacitor size based on necessary low frequency response,

turn-on pops can be minimized.

SELECTING THE AUDIO AMPLIFIER’S BYPASS

CAPACITOR

Besides minimizing the input capacitor size, careful consid-

eration should be paid to the bypass capacitor value. Bypass

capacitor, C

, is the most critical component to minimize

turn-on pops since it determines how fast the amplifer turns

on. The slower the amplifier’s outputs ramp to their quies-

cent DC voltage (nominally 1/2 V

), the smaller the turn-on

pop. Choosing C

equal to 1.0µF along with a small value of

(in the range of 0.039µF to 0.39µF), should produce a

virtually clickless and popless shutdown function. While the

device will function properly, (no oscillations or motorboat-

ing), with C

equal to 0.1µF, the device will be much more

susceptible to turn-on clicks and pops. Thus, a value of C

equal to 1.0µF is recommended in all but the most cost

sensitive designs.

OPERATING PRINCIPLE

The LM4804 includes step-up DC-DC voltage regulation for

battery-powered and low-input voltage systems. It combines

a step-up switching regulator, N-channel power MOSFET,

built-in current limit, thermal limit, and voltage reference. The

switching DC-DC regulator boosts an input voltage between

.8V and 14V to a regulated output voltage between 1.24V

and 14V. The LM4804 starts from a low 1.1V input and

remains operational down to below .8V.

This device is optimized for use in cellular phones and other

applications requiring a small size, low profile, as well as low

quiescent current for maximum battery life during stand-by

and shutdown.

Additional features include a built-in peak switch current

limit, a high-efficiency gated-oscillator topology that offers an

output of up to 2A at low output voltages, and thermal

protection circuitry.

LM4804

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Application Information (Continued)

GATED OSCILLATOR CONTROL SCHEME

The on/off regulation mode of the LM4804, along with its

ultra-low quiescent current, results in good efficiency over a

very wide load range. The internal oscillator frequency can

be programmed using an external resistor to be constant or

vary with the battery voltage. Adding a capacitor to program

the frequency allows the designer to adjust the duty cycle

and optimize it for the application. Adding a resistor in addi-

tion to the capacitor allows the duty cycle to dynamically

compensate for changes to the input/output voltage ratio.

We call this a Ratio Adaptive Gated Oscillator circuit. Using

the correct RC components to adjust the oscillator allows the

part to run with low ripple and high efficiency over a wide

range of loads and input/output voltages.

201167C0

FIGURE 2. Functional Diagram of the LM4804’s Regulator

201167C1

FIGURE 3. Typical Step-Up Regulator Waveforms

LM4804

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Application Information (Continued)

PULSE FREQUENCY MODULATION (PFM)

Pulse Frequency Modulation is typically accomplished by

switching continuously until the voltage limit is reached and

skipping cycles after that to just maintain it. This results in a

somewhat hysteretic mode of operation. The coil stores

more energy each cycle as the current ramps up to high

levels. When the voltage limit is reached, the system usually

overshoots to a higher voltage than required, due to the

stored energy in the coil (see Figure 3). The system will also

undershoot somewhat when it starts switching again be-

cause it has depleted all the stored energy in the coil and

needs to store more energy to reach equilibrium with the

load. Larger output capacitors and smaller inductors reduce

the ripple in these situations. The frequency being filtered,

however, is not the basic switching frequency. It is a lower

frequency determined by the load, the input/output voltage

and the circuit parameters. This mode of operation is useful

in situations where the load variation is significant. Power

managed computer systems, for instance, may vary from

zero to full load while the system is on and this is usually the

preferred regulation mode for such systems.

CYCLE TO CYCLE PFM

When the load doesn’t vary over a wide range (like zero to

full load), ratio adaptive circuit techniques can be used to

achieve cycle to cycle PFM regulation and lower ripple (or

smaller output capacitors). The key to success here is

matching the duty cycle of the circuit closely to what is

required by the input to output voltage ratio. This ratio then

needs to be dynamically adjusted for input voltage changes

(usually caused by batteries running down). The chosen

ratio should allow most of the energy in each switching cycle

to be delivered to the load and only a small amount to be

stored. When the regulation limit is reached, the overshoot

will be small and the system will settle at an equilibrium point

where it adjusts the off time in each switching cycle to meet

the current requirements of the load. The off time adjustment

is done by exceeding the regulation limit during each switch-

ing cycle and waiting until the voltage drops below the limit

again to start the next switching cycle. The current in the coil

never goes to zero like it frequently does in the hysteretic

operating mode of circuits with wide load variations or duty

cycles that aren’t matched to the input/output voltage ratio.

Optimizing the duty cycle for a given set of input/output

voltages conditions can be done by using the circuit values

in the Application Notes.

LOW VOLTAGE START-UP

The LM4804 can start-up from voltages as low as 1.1 volts.

On start-up, the control circuitry switches the N-channel

MOSFET continuously until the output reaches 3 volts. After

this output voltage is reached, the normal step-up regulator

feedback and gated oscillator control scheme take over.

Once the device is in regulation, it can operate down to

below .8V input, since the internal power for the IC can be

boot-strapped from the output using the Vdd pin.

SHUT DOWN

The LM4804 features a shutdown mode that reduces the

quiescent current to less than a guaranteed 2.5uA over

temperature. This extends the life of the battery in battery

powered applications. During shutdown, all feedback and

control circuitry is turned off. The regulator’s output voltage

drops to one diode drop below the input voltage. Entry into

the shutdown mode is controlled by the active-low logic input

pin S/D1 (pin 26). When the logic input to this pin is pulled

below 0.15V

, the device goes into shutdown mode. The

logic input to this pin should be above 0.7V

for the device

to work in normal step-up mode.

SELECTING OUTPUT CAPACITOR (C

) FOR BOOST

CONVERTER

A single ceramic capacitor of value 4.7µF to 10µF will pro-

vide sufficient output capacitance for most applications. If

larger amounts of capacitance are desired for improved line

support and transient response, tantalum capacitors can be

used. Aluminum electrolytics with ultra low ESR such as

Sanyo Oscon can be used, but are usually prohibitively

expensive. Typical AI electrolytic capacitors are not suitable

for switching frequencies above 500 kHz due to significant

ringing and temperature rise due to self-heating from ripple

current. An output capacitor with excessive ESR can also

reduce phase margin and cause instability.

In general, if electrolytics are used, it is recommended that

they be paralleled with ceramic capacitors to reduce ringing,

switching losses, and output voltage ripple.

INTERNAL CURRENT LIMIT AND THERMAL

PROTECTION

An internal cycle-by-cycle current limit serves as a protection

feature. This is set high enough (2.85A typical, approxi-

mately 4A maximum) so as not to come into effect during

normal operating conditions. An internal thermal protection

circuit disables the MOSFET power switch when the junction

temperature (T

) exceeds about 160˚C. The switch is re-

enabled when T

drops below approximately 135˚C.

NON-LINEAR EFFECT

The LM4804 takes advantage of a non-linear effect that

allows for the duty cycle to be programmable. The C3 ca-

pacitor is used to dump charge on the FREQ pin in order to

manipulate the duty cycle of the internal oscillator. The part

is being tricked to behave in a certain manner, in the effort to

make this Pulse Frequency Modulated (PFM) boost switch-

ing regulator behave as a Pulse Width Modulated (PWM)

boost switching regulator.

CHOOSING THE CORRECT C3 CAPACITOR

The C3 capacitor allows for the duty cycle of the internal

oscillator to be programmable. Choosing the correct C3

capacitor to get the appropriate duty cycle for a particular

application circuit is a trial and error process. The non-linear

effect that C3 produces is dependent on the input voltage

and output voltage values. The correct C3 capacitor for

particular input and output voltage values cannot be calcu-

lated. Choosing the correct C3 capacitance is best done by

trial and error, in conjunction with the checking of the induc-

tor peak current to make sure your not too close to the

current limit of the device. As the C3 capacitor value in-

creases, so does the duty cycle. And conversely as the C3

capacitor value decreases, the duty cycle decreases. An

incorrect choice of the C3 capacitor can result in the part

prematurely tripping the current limit and/or double pulsing,

which could lead to the output voltage not being stable.

SETTING THE OUTPUT VOLTAGE

The output voltage of the step-up regulator can be set by

connecting a feedback resistive divider made of R

and

. The resistor values are selected as follows:

[(V

OUT

/1.24) −1]

LM4804

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Application Information (Continued)

A value of 50k to 100k is suggested for R

. Then, R

can be

selected using the above equation.

SUPPLY

The Vdd supply must be between 3 to 5 volts for the

LM4804. This voltage can be bootstrapped from a much

lower input voltage by simply connecting the V

pin to

OUT

. In the event that the V

supply voltage is not a low

ripple voltage source (less than 200 millivolts), it may be

advisable to use an RC filter to clean it up. Excessive ripple

on V

may reduce the efficiency.

SETTING THE SWITCHING FREQUENCY

The switching frequency of the oscillator is selected by

choosing an external resistor (R3) connected between V

and the FREQ pin. See the graph titled "Frequency vs V

“in

the Typical Performance Characteristics section of the data

sheet for choosing the R3 value to achieve the desired

switching frequency. A high switching frequency allows the

use of very small surface mount inductors and capacitors

and results in a very small solution size. A switching fre-

quency between 300kHz and 2MHz is recommended.

OUTPUT DIODE SELECTION

A Schottky diode should be used for the output diode. The

forward current rating of the diode should be higher than the

peak input current, and the reverse voltage rating must be

higher than the output voltage. Do not use ordinary rectifier

diodes, since slow switching speeds and long recovery times

cause the efficiency and the load regulation to suffer. Table 1

shows a list of the diode manufacturers.

LLP PACKAGE DEVICES

The LM4804 is offered in the 14 lead LLP surface mount

package to allow for increased power dissipation compared

to the MSOP-8. For details of the thermal performance as

well as mounting and soldering specifications, refer to Ap-

plication Note AN-1187.

RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT

Figure 5 through Figure 10 show the recommended four-

layer PC board layout that is optimized for the LQ-packaged,

3V 1.7W LM4804 mono-BTL audio amplifier and its associ-

ated external components. This circuit is designed for use

with an external 3V to 4.2V supply and speakers with 4Ωor

higher impedance (8Ωnominal).

The LM4804 circuit board is easy to use. Apply between 3V

and 4.2V (equivalent to, respectfully, a discharged or a fully

charged Li-ion or NMH battery) and ground to JP2’s V

and

GND pins, respectively. Connect a speaker with an imped-

ance of 4Ωor greater (8Ωnominal) between the board’s

VO1 (-) and VO2 (+) pins. An audio signal is applied to JP1

between the V

(+) and GND (-) pins.

The circuit board is configured for a gain of 20 or 26dB (VO2

-VO1 with respect to VIN). An inverting gain of -10 at VO1 is

set by Rf (200kΩ) versus Ri (20kΩ). The extra gain of 2 is a

product of the BTL output (VO2 - VO1). Gain can be modi-

fied by changing Rf’s value with respect to Ri.

TABLE 1. Suggested Manufacturers List

Inductors Capacitors Diodes

Coilcraft

Tel: (800) 322-2645

Fax: (708) 639-1469

Sprague/ Vishay

Tel: (207) 324-4140

Fax: (207) 324-7223

Motorola

Tel: (800) 521-6274

Fax: (602) 244-6609

Coiltronics

Tel: (407) 241-7876

Fax: (407) 241-9339

Kemet

Tel: (864) 963-6300

Fax: (864) 963-6521

International Rectifier (IR)

Tel: (310) 322-3331

Fax: (310) 322-3332

Pulse Engineering

Tel: (619) 674-8100

Fax: (619) 674-8262

Nichicon

Tel: (847) 843-7500

Fax: (847) 843-2798

General Semiconductor

Tel: (516) 847-3222

Fax: (516) 847-3150

LM4804

www.national.com 12

Application Information (Continued)

20116714

FIGURE 4. Demo Board Reference Schematic

LM4804

www.national.com13

Demonstration Board Layout

20116720

FIGURE 5. Top Trace Layer Silkscreen

20116718

FIGURE 6. Top Layer Silkscreen

20116719

FIGURE 7. Top Trace Layer

20116716

FIGURE 8. Upper Internal GND Layer

LM4804

www.national.com 14

Demonstration Board Layout (Continued)

20116717

FIGURE 9. Lower Internal V

Layer

20116715

FIGURE 10. Bottom Trace Layer with GND Plane

LM4804

www.national.com15

Revision History

Rev Date Description

1.0 6/14/05 Under SHUTDOWN (Apps section), changed EN to

S/D1 and (pin– 2) into pin 26, then re-released D/S to

the WEB.

LM4804

www.national.com 16

Physical Dimensions inches (millimeters)

unless otherwise noted

LQ Package

Order Number LM4804LQ

NS Package Number LQA28A

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves

the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS

WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR

CORPORATION. As used herein:

1. Life support devices or systems are devices or systems

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.

2. A critical component is any component of 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.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products

Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain

no ‘‘Banned Substances’’ as defined in CSP-9-111S2.

Leadfree products are RoHS compliant.

National Semiconductor

Americas Customer

Support Center

Email: new.feedback@nsc.com

Tel: 1-800-272-9959

National Semiconductor

Europe Customer Support Center

Fax: +49 (0) 180-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 69 9508 6208

English Tel: +44 (0) 870 24 0 2171

Français Tel: +33 (0) 1 41 91 8790

National Semiconductor

Asia Pacific Customer

Support Center

Email: ap.support@nsc.com

National Semiconductor

Japan Customer Support Center

Fax: 81-3-5639-7507

Email: jpn.feedback@nsc.com

Tel: 81-3-5639-7560

www.national.com

LM4804 Low Voltage High Power Audio Power Amplifier

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