then either the supply voltage must be decreased, the load

impedance increased, the ambient temperature reduced, or

the

θ

traces near the output, V

lower the

θ

heatsinking allowing higher power dissipation. For the typical

application of a 5V power supply, with a 16

Ω load power

dissipation is not an issue. Recall that internal power dissi-

pation is a function of output power. If typical operation is not

around the maximum power dissipation point, the LM4915

can operate at higher ambient temperatures. Refer to the

Typical Performance Characteristics curves for power dis-

sipation information.

POWER SUPPLY BYPASSING

As with any power amplifier, proper supply bypassing is

critical for low noise performance and high power supply

rejection ratio (PSRR). The capacitor location on both the

bypass and power supply pins should be as close to the

device as possible. A larger half-supply bypass capacitor

improves PSRR because it increases half-supply stability.

Typical applications employ a 5V regulator with 10µF and

0.1µF bypass capacitors that increase supply stability. This,

however, does not eliminate the need for bypassing the

supply nodes of the LM4915. A 1µF capacitor is recom-

mended for C

This value coupled with small input capacitors (0.1µF to

0.47µF) gives virtually zero click and pop with outstanding

PSRR performance.

MICRO POWER SHUTDOWN

The voltage applied to the SHUTDOWN pin controls the

LM4915’s shutdown function. Activate micro-power shut-

down by applying a logic-low voltage to the SHUTDOWN

pin. When active, the LM4915’s micro-power shutdown fea-

ture turns off the amplifier’s bias circuitry, reducing the sup-

ply current. The trigger point is 0.4V for a logic-low level, and

1.8V for a logic-high level. The low 0.1µA (typ) shutdown

current is achieved by applying a voltage that is as near as

ground as possible to the SHUTDOWN pin. A voltage that is

higher than ground may increase the shutdown current.

There are a few ways to control the micro-power shutdown.

These include using a single-pole, single-throw switch, a

microprocessor, or a microcontroller. When using a switch,

connect an external 100k. pull-up resistor between the

SHUTDOWN pin and V

SHUTDOWN pin and ground. Select normal amplifier opera-

tion by opening the switch. Closing the switch connects the

SHUTDOWN pin to ground, activating micro-power shut-

down.

The switch and resistor guarantee that the SHUTDOWN pin

will not float. This prevents unwanted state changes. In a

system with a microprocessor or microcontroller, use a digi-

tal output to apply the control voltage to the SHUTDOWN

pin. Driving the SHUTDOWN pin with active circuitry elimi-

nates the pull-up resistor.

PROPER SELECTION OF EXTERNAL COMPONENTS

Proper selection of external components in applications us-

ing integrated power amplifiers is critical to optimize device

and system performance. While the LM4915 is tolerant of

external component combinations, and requires minimal ex-

ternal components, consideration to component values must

be used to maximize overall system quality.

The input coupling capacitor, C

filter which limits low frequency response given by f

1/(2

πR

Ω. This value should be

chosen based on needed frequency response for a few

distinct reasons.

Selection of Input Capacitor Size

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 in many cases the 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 perfor-

mance.

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

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

C

reach its quiescent DC voltage (nominally 1/2 V

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

Besides minimizing the input capacitor size, careful consid-

eration should be paid to the bypass capacitor value. Bypass

capacitor, C

turn-on pops since it determines how fast the LM4915 turns

on. The slower the LM4915’s outputs ramp to their quiescent

DC voltage (nominally 1/2 V

Choosing C

the range of 0.1µF to 0.47µF), should produce a virtually

clickless and popless shutdown function. While the device

will function properly, (no oscillations or motorboating), with

C

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

4.7µF is recommended in all but the most cost sensitive

designs.

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