creased, the load impedance increased or T

the typical application of a 5V power supply, with a 32

Ω load,

the maximum ambient temperature possible without violating

the maximum junction temperature is approximately 133.2˚C

provided that device operation is around the maximum

power dissipation point. 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 accordingly. Refer to the Typical Perfor-

mance Characteristics curves for power dissipation infor-

mation for lower output powers.

POWER SUPPLY BYPASSING

As with any power amplifier, proper supply bypassing is

critical for low noise performance and high power supply

rejection. Applications that employ a 5V regulator typically

use a 10µF in parallel with a 0.1µF filter capacitors to stabi-

lize the regulator’s output, reduce noise on the supply line,

and improve the supply’s transient response. However, their

presence does not eliminate the need for a local 1.0µF

tantalum bypass capacitance connected between the

LM4810’s supply pins and ground. Keep the length of leads

and traces that connect capacitors between the LM4810’s

power supply pin and ground as short as possible. Connect-

ing a 4.7µF capacitor, C

ground improves the internal bias voltage’s stability and

improves the amplifier’s PSRR. The PSRR improvements

increase as the bypass pin capacitor value increases. Too

large, however, increases the amplifier’s turn-on time. The

selection of bypass capacitor values, especially C

on desired PSRR requirements, click and pop performance

(as explained in the section, Selecting Proper External

Components), system cost, and size constraints.

SELECTING PROPER EXTERNAL COMPONENTS

Optimizing the LM4810’s performance requires properly se-

lecting external components. Though the LM4810 operates

well when using external components with wide tolerances,

best performance is achieved by optimizing component val-

ues.

The LM4810 is unity-gain stable, giving a designer maximum

design flexibility. The gain should be set to no more than a

given application requires. This allows the amplifier to

achieve minimum THD+N and maximum signal-to-noise ra-

tio. These parameters are compromised as the closed-loop

gain increases. However, low gain demands input signals

with greater voltage swings to achieve maximum output

power. Fortunately, many signal sources such as audio

CODECs have outputs of 1V

the Audio Power Amplifier Design section for more infor-

mation on selecting the proper gain.

Input and Output Capacitor Value Selection

Amplifying the lowest audio frequencies requires high value

input and output coupling capacitors (C

A high value capacitor can be expensive and may compro-

mise space efficiency in portable designs. In many cases,

however, the speakers used in portable systems, whether

internal or external, have little ability to reproduce signals

below 150Hz. Applications using speakers with this limited

frequency response reap little improvement by using high

value input and output capacitors.

Besides affecting system cost and size, C

the LM4810’s click and pop performance. The magnitude of

the pop is directly proportional to the input capacitor’s size.

Thus, pops can be minimized by selecting an input capacitor

value that is no higher than necessary to meet the desired

−3dB frequency. Please refer to the Optimizing Click and

Pop Reduction Performance section for a more detailed

discussion on click and pop performance.

As shown in Figure 1, the input resistor, R

capacitor, C

quency that is found using Equation (3). In addition, the

output load R

high pass filter cutoff frequency defined by Equation (4).

f

πR

(3)

f

πR

(4)

Also, careful consideration must be taken in selecting a

certain type of capacitor to be used in the system. Different

types of capacitors (tantalum, electrolytic, ceramic) have

unique performance characteristics and may affect overall

system performance.

Bypass Capacitor Value Selection

Besides minimizing the input capacitor size, careful consid-

eration should be paid to the value of C

connected to the BYPASS pin. Since C

fast the LM4810 settles to quiescent operation, its value is

critical when minimizing turn-on pops. The slower the

LM4810’s outputs ramp to their quiescent DC voltage (nomi-

nally 1/2 V

equal to 4.7µF along with a small value of C

0.1µF to 0.47µF), produces a click-less and pop-less shut-

down function. As discussed above, choosing C

than necessary for the desired bandwith helps minimize

clicks and pops.

OPTIMIZING CLICK AND POP REDUCTION

PERFORMANCE

The LM4810 contains circuitry that minimizes turn-on and

shutdown transients or “clicks and pop”. For this discussion,

turn-on refers to either applying the power supply voltage or

when the shutdown mode is deactivated. During turn-on, the

LM4810’s internal amplifiers are configured as unity gain

buffers. An internal current source charges up the capacitor

on the BYPASS pin in a controlled, linear manner. The gain

of the internal amplifiers remains unity until the voltage on

the BYPASS pin reaches 1/2 V

the BYPASS pin is stable, the device becomes fully opera-

tional. During device turn-on, a transient (pop) is created

from a voltage difference between the input and output of the

amplifier as the voltage on the BYPASS pin reaches 1/2 V

For this discussion, the input of the amplifier refers to the

node between R

the voltage applied to the BYPASS pin. During turn-on, the

buffer-configured amplifier output charges the input capaci-

tor, C

delays the charging time of C

difference between the input and output that results in a

transient (pop). Higher value capacitors need more time to

reach a quiescent DC voltage (usually 1/2 V

when

charged with a fixed current. Decreasing the value of C

R

desired -3dB frequency.

Although the BYPASS pin current cannot be modified,

changing the size of C

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