LM4916

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SNAS179E – MAY 2003 – REVISED MAY 2013

POWER DISSIPATION

Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or

single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an

increase in internal power dissipation. Since the LM4916 has two operational amplifiers in one package, the

maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation

for a given BTL application can be derived from the power dissipation graphs or from Equation 3.

PDMAX = 4*(VDD)

2 / (2π2R

L)

(3)

When operating in Single Ended mode, Equation 4 states the maximum power dissipation point for a single-

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

PDMAX = (VDD)

2 / (2π2R

L)

(4)

Since the LM4916 has two operational amplifiers in one package, the maximum internal power dissipation point

is twice that of the number that results from Equation 4. From Equation 4, assuming a 1.5V power supply and a

16

Ω load, the maximum power dissipation point is 7mW per amplifier. Thus the maximum package dissipation

point is 14mW.

The maximum power dissipation point obtained from either Equation 3 or Equation 4must not be greater than the

power dissipation that results from Equation 5:

PDMAX = (TJMAX - TA) / θJA

(5)

For package DGS0010A,

θJA = 175°C/W. TJMAX = 150°C for the LM4916. Depending on the ambient

temperature, TA, of the system surroundings, Equation 5 can be used to find the maximum internal power

dissipation supported by the IC packaging. If the result of Equation 3 or Equation 4 is greater than that of

Equation 5, then either the supply voltage must be decreased, the load impedance increased or TA reduced. For

the typical application of a 1.5V power supply, with a 16

Ω load, the maximum ambient temperature possible

without violating the maximum junction temperature is approximately 146°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 LM4916'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. 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.

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 battery (or 1.5V regulator) with 10µF tantalum or electrolytic capacitor and a ceramic

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

the LM4916. A bypass capacitor value in the range of 0.1µF to 1µF is recommended.

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