LM4911, LM4911Q

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SNAS152M – MAY 2004 – REVISED JUNE 2011

POWER DISSIPATION

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

ensure a successful design. When operating in capacitor-coupled mode, 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 LM4911/LM4911Q has two operational amplifiers in one package, the maximum internal power

dissipation point is twice that of the number which results from Equation 1. From Equation 1, assuming a 3V

power supply and an 32

Ω load, the maximum power dissipation point is 14mW per amplifier. Thus the maximum

package dissipation point is 28mW.

When operating in OCL mode, the maximum power dissipation increases due to the use of the third amplifier as

a buffer and is given in Equation 2:

(2)

The maximum power dissipation point obtained from either Equation 1 or Equation 2 must not be greater than

the power dissipation that results from Equation 3:

(3)

For package DGS0010A,

used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 1 or

Equation 2 is greater than that of Equation 3, then either the supply voltage must be decreased, the load

maximum ambient temperature possible without violating the maximum junction temperature is approximately

144°C provided that device operation is around the maximum power dissipation point. Thus, for typical

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

accordingly. Refer to the Typical Performance Characteristics curves for power dissipation information for lower

output powers.

EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS

The LM4911/LM4911Q's exposed-DAP (die attach paddle) package (WSON) 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 WSON 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

WSON package is available from TI's Package Engineering Group under application note AN-1187 (SNOA401).

POWER SUPPLY BYPASSING

As with any amplifier, proper supply bypassing is important for low noise performance and high power supply

rejection. The capacitor location on the power supply pins should be as close to the device as possible.

Typical applications employ a 3V regulator with 10mF tantalum or electrolytic capacitor and a ceramic bypass

capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the

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