LM4856 datasheet(16/23 Pages) NSC

16 / 23 page

Application Information (Continued)

TABLE 3. Volume Control

Gain (dB)

IN,LIN

OUT,LOUT

00000

-34.5

-40.5

00001

-33.0

-39.0

00010

-31.5

-37.5

00011

-30.0

-36.0

00100

-28.5

-34.5

00101

-27.0

-33.0

00110

-25.5

-31.5

00111

-24.0

-30.0

01000

-22.5

-28.5

01001

-21.0

-27.0

01010

-19.5

-25.5

01011

-18.0

-24.0

01100

-16.5

-22.5

01101

-15.0

-21.0

01110

-13.5

-19.5

01111

-12.0

-18.0

10000

-10.5

-16.5

10001

-9.0

-15.0

10010

-7.5

-13.5

10011

-6.0

-12.0

10100

-4.5

-10.5

10101

-3.0

-9.0

10110

-1.5

-7.5

10111

0.0

-6.0

11000

1.5

-4.5

11001

3.0

-3.0

11010

4.5

-1.5

11011

6.0

0.0

11100

7.5

1.5

11101

9.0

3.0

11110

10.5

4.5

11111

12.0

6.0

EXPOSED-DAP MOUNTING CONSIDERATIONS

The LM4856’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 area heatsink, copper traces, ground plane, and

finally, surrounding air. The result is a low voltage audio

power amplifier that produces 1.1W dissipation in a 8

Ω load

≤ 1% THD+N. This high power is achieved through careful

consideration of necessary thermal design. Failing to opti-

mize thermal design may compromise the LM4856’s high

power performance and activate unwanted, though neces-

sary, thermal shutdown protection.

The LD package must have its DAP soldered to a copper

pad on the PCB. The DAP’s PCB copper pad is then, ideally,

connected to a large plane of continuous unbroken copper.

This plane forms a thermal mass, heat sink, and radiation

area. Place the heat sink area on either outside plane in the

case of a two-sided or multi-layer PCB. (The heat sink area

can also be placed on an inner layer of a multi-layer board.

The thermal resistance, however, will be higher.) Connect

the DAP copper pad to the inner layer or backside copper

heat sink area with 6 (3 X 2) (LD) vias. The via diameter

should be 0.012in - 0.013in with a 1.27mm pitch. Ensure

efficient thermal conductivity by plugging and tenting the vias

with plating and solder mask, respectively.

Best thermal performance is achieved with the largest prac-

tical copper heat sink area. If the heatsink and amplifier

share the same PCB layer, a nominal 2.5in

2 (min) area is

necessary for 5V operation with a 4

Ω load. Heatsink areas

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