LM4752 datasheet(13/18 Pages) NSC

13 / 18 page

Application Information (Continued)

TO-263 HEATSINK DESIGN EXAMPLES:

Example 1: (Stereo Single-Ended Output)

Given:

A=30˚C

J=150˚C

L=4Ω

S=12V

JC=2˚C/W

DMAX from PD vs PO Graph:

DMAX ≈ 3.7W

Calculating P

DMAX:

DMAX = VCC

2 /(

π2R

L) = (12V)

2 /

π2(4Ω)) = 3.65W

Calculating Heatsink Thermal Resistance:

SA < [(T J −TA)/PDMAX]− θJC − θCS

SA < 120˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 30.2˚C/W

Therefore the recommendation is to use 1.5 x 1.5 square

inch of single-sided copper clad.

Example 2: (Stereo Single-Ended Output)

Given:

A=50˚C

J=150˚C

L=4Ω

S=12V

JC=2˚C/W

DMAX from PD vs PO Graph:

DMAX ≈ 3.7W

Calculating P

DMAX:

DMAX = VCC

2 /(

π2R

L) = (12V)

2 /(

π2(4Ω)) = 3.65W

Calculating Heatsink Thermal Resistance:

SA < [(TJ −TA)/PDMAX]− θJC − θCS

SA < 100˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 24.8˚C/W

Therefore the recommendation is to use 2.0 x 2.0 square

inch of single-sided copper clad.

Example 3: (Bridged Output)

Given:

A=50˚C

J=150˚C

L=8Ω

S=12V

JC=2˚C/W

Calculating P

DMAX:

DMAX = 4[VCC

2 /(2

π2R

L)] = 4(12V)

2 /(2

π2(8Ω)) = 3.65W

Calculating Heatsink Thermal Resistance:

SA < [(TJ −TA)/PDMAX]− θJC − θCS

SA < 100˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 24.8˚C/W

Therefore the recommendation is to use 2.0 x 2.0 square

inch of single-sided copper clad.

Layout and Ground Returns

Proper PC board layout is essential for good circuit perfor-

mance. When laying out a PC board for an audio power am-

plifer, particular attention must be paid to the routing of the

output signal ground returns relative to the input signal and

bias capacitor grounds. To prevent any ground loops, the

ground returns for the output signals should be routed sepa-

rately and brought together at the supply ground. The input

signal grounds and the bias capacitor ground line should

also be routed separately. The 0.1 µF high frequency supply

bypass capacitor should be placed as close as possible to

the IC.

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