LDC08A datasheet(10/15 Pages) NSC

10 / 15 page

Typical Performance Characteristics (Continued)

Output Power vs

Supply Voltage, R

L =16

Ω

Output Power vs

Supply Voltage, R

L =32

Ω

20074069

20074070

Frequency Response vs

Input Capacitor Size

20074071

Application Information

EXPOSED-DAP PACKAGE PCB MOUNTING

CONSIDERATION

The LM4991’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

result is a low voltage audio power amplifier that produces

2W at

≤ 1% THD with a 4Ω load. This high power is achieved

through careful consideration of necessary thermal design.

Failing to optimize thermal design may compromise the

LM4991’s high power performance and activate unwanted,

though necessary, 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 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 PCB, or on an inner layer of a board with more

than two layers. Connect the DAP copper pad to the inner

layer or backside copper heat sink area with 4(2x2) vias. The

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

Ensure efficient thermal conductivity by plating through the

vias.

Best thermal performance is achieved with the largest prac-

tical heat sink area. If the heatsink and amplifier share the

same PCB layer, a nominal 2.5in

2 area is necessary for 5V

operation with a 4

Ω load. Heatsink areas not placed on the

same PCB layer as the LM4991 should be 5in

2 (min) for the

same supply voltage and load resistance. The last two area

recommendations apply for 25˚C ambient temperature. In-

crease the area to compensate for ambient temperatures

above 25˚C. The LM4991’s power de-rating curve in the

Typical Performance Characteristics shows the maximum

power dissipation versus temperature. An example PCB lay-

out for the LD package is shown in the Demonstration

Board Layout section. Further detailed and specific infor-

mation concerning PCB layout, fabrication, and mounting an

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