LM4808

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SNAS051D – FEBRUARY 2000 – REVISED MAY 2013

APPLICATION INFORMATION

EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION

The LM4808'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.

However, since the LM4808 is designed for headphone applications, connecting a copper plane to the DAP's

PCB copper pad is not required. The LM4808's Power Dissipation vs Output Power Curve in the TYPICAL

PERFORMANCE CHARACTERISTICS shows that the maximum power dissipated is just 45mW per amplifier

with a 5V power supply and a 32

Ω load.

Further detailed and specific information concerning PCB layout, fabrication, and mounting an LD (WSON)

package is available from Texas Instruments' Package Engineering Group under application note AN-1187

(literature number SNOA401).

POWER DISSIPATION

Power dissipation is a major concern when using any power amplifier and must be thoroughly understood to

ensure a successful design. Equation 1 states the maximum power dissipation point for a single-ended amplifier

operating at a given supply voltage and driving a specified output load.

(1)

Since the LM4808 has two operational amplifiers in one package, the maximum internal power dissipation point

is twice that of the number which results from Equation 1. Even with the large internal power dissipation, the

LM4808 does not require heat sinking over a large range of ambient temperature. From Equation 1, assuming a

5V power supply and a 32

Ω load, the maximum power dissipation point is 40mW per amplifier. Thus the

maximum package dissipation point is 80mW. The maximum power dissipation point obtained must not be

greater than the power dissipation that results from Equation 2:

where

•

•

(2)

maximum internal power dissipation supported by the IC packaging. If the result of Equation 1 is greater than

reduced. For 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 PERFORMANCE CHARACTERISTICS curves for power

dissipation information 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

stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient response.

between the LM4808's supply pins and ground. Keep the length of leads and traces that connect capacitors

between the IN A(+) / IN B(+) node and 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,

on desired PSRR requirements, click and pop performance (as explained in the section, SELECTING PROPER

EXTERNAL COMPONENTS), system cost, and size constraints.

Copyright © 2000–2013, Texas Instruments Incorporated

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