PCB, the LM4883SQ’s

θ

temperature T

nal power dissipation supported by the IC packaging. Rear-

ranging Equation (4) and substituting P

sults in Equation (5). This equation gives the maximum

ambient temperature that still allows maximum stereo power

dissipation without violating the LM4883’s maximum junction

temperature.

T

θ

JA

(5)

For a typical application with a 5V power supply and an 4

Ω

load, the maximum ambient temperature that allows maxi-

mum stereo power dissipation without exceeding the maxi-

mum junction temperature is approximately 99˚C for the SQ

package.

T

θ

(6)

Equation (6) gives the maximum junction temperature

T

maximum junction temperature by reducing the power sup-

ply voltage or increasing the load resistance. Further allow-

ance should be made for increased ambient temperatures.

The above examples assume that a device is a surface

mount part operating around the maximum power dissipation

point. Since internal power dissipation is a function of output

power, higher ambient temperatures are allowed as output

power or duty cycle decreases.

If the result of Equation (2) is greater than that of Equation

(3), then decrease the supply voltage, increase the load

impedance, or reduce the ambient temperature. If these

measures are insufficient, a heat sink can be added to

reduce

θ

copper area around the package, with connections to the

ground pin(s), supply pin and amplifier output pins. External,

solder attached SMT heatsinks such as the Thermalloy

7106D can also improve power dissipation. When adding a

heat sink, the

θ

θ

θ

θ

θ

junction-to-case thermal impedance,

θ

thermal impedance, and

θ

impedance.) Refer to the Typical Performance Character-

istics curves for power dissipation information at lower out-

put power levels.

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 10 µF in parallel with a 0.1 µF filter capacitor to

stabilize 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 1.0 µF

tantalum bypass capacitance connected between the

LM4883’s supply pins and ground. Do not substitute a ce-

ramic capacitor for the tantalum. Doing so may cause oscil-

lation. Keep the length of leads and traces that connect

capacitors between the LM4883SQ’s power supply pin and

ground as short as possible. Connecting a 1µF capacitor, C

between the BYPASS pin and ground improves the internal

bias voltage’s stability and improves the amplifier’s PSRR.

The PSRR improvements increase as the bypass pin ca-

pacitor value increases. Too large, however, increases

turn-on time and can compromise amplifier’s click and pop

performance. The selection of bypass capacitor values, es-

pecially C

and pop performance (as explained in the section, Selecting

Proper External Components), system cost, and size con-

straints.

MICRO-POWER SHUTDOWN

The voltage applied to the SHUTDOWN pin controls the

LM4883’s shutdown function. Activate micro-power shut-

down by applying V

the LM4883’s micro-power shutdown feature turns off the

amplifier’s bias circuitry, reducing the supply current. The

logic threshold is typically V

shutdown current is achieved by applying a voltage that is as

near as V

that is less than V

Table 1 shows the logic signal levels that activate and deac-

tivate micro-power shutdown and headphone amplifier op-

eration.

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 10k

Ω pull-up resistor between the

SHUTDOWN pin and V

SHUTDOWN pin and ground. Select normal amplifier opera-

tion by closing the switch. Opening the switch connects the

SHUTDOWN pin to V

ing micro-power shutdown. The switch and resistor guaran-

tee that the SHUTDOWN pin will not float. This prevents

unwanted state changes. In a system with a microprocessor

or a microcontroller, use a digital output to apply the control

voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin

with active circuitry eliminates the pull up resistor.

TABLE 1. Logic Level Truth Table for SHUTDOWN, HP-IN, and MUX Operation

SHUTDOWN

PIN

HP-INPIN

MUX CHANNEL

SELECT PIN

OPERATIONAL MODE

(MUX INPUT CHANNEL #)

Logic Low

Logic Low

Logic Low

Bridged Amplifiers (1)

Logic Low

Logic Low

Logic High

Bridged Amplifiers (2)

Logic Low

Logic High

Logic Low

Single-Ended Amplifiers (1)

Logic Low

Logic High

Logic High

Single-Ended Amplifiers (2)

Logic High

X

X

Micro-Power Shutdown

HP-IN FUNCTION

Applying a voltage between 4V and V

HP-IN headphone control pin turns off Amp A (+out) and Amp

B (+out) muting a bridged-connected load. Quiescent current

consumption is reduced when the IC is in this single-ended

mode.

Figure 4 shows the implementation of the LM4883’s head-

phone control function. With no headphones connected to

the headphone jack, the R9-R10 voltage divider sets the

voltage applied to the HP-IN pin (pin 20) at approximately

50mV. This 50mV enables Amp A (+out) and Amp B (+out)

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