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Trace Width

EFFICIENCY AND THERMAL INFORMATION

q

JA

+

1

Derating Factor

+

1

0.041

+ 24

°C W

(3)

T

A

Max + TJMax * qJAPDmax + 150 * 24 (1.5) + 114°C

(4)

OPERATION WITH DACs AND CODECs

FILTER FREE OPERATION AND FERRITE BEAD FILTERS

1 nF

Ferrite

Chip Bead

OUTP

OUTN

Ferrite

Chip Bead

1 nF

TPA2012D2

SLOS438C – DECEMBER 2004 – REVISED MARCH 2007

Recommended trace width at the solder balls is 75

µm to 100 µm to prevent solder wicking onto wider PCB

traces.

solder balls and at least 500-

µm PCB traces to ensure proper performance and output power for the device.

For the remaining signals of the TPA2012D2, use 75-

µm to 100-µm trace widths at the solder balls. The audio

input pins (INR+/- and INL+/-) must run side-by-side to maximize common-mode noise cancellation.

The maximum ambient temperature depends on the heat-sinking ability of the PCB system. The derating factor

for the packages are shown in the dissipation rating table. Converting this to

θ

Given

θ

dissipation of 1.5W (0.75 W per channel) for 2.1 W per channel, 4-

Ω load, 5-V supply, from Figure 25, the

maximum ambient temperature can be calculated with the following equation.

Equation 4 shows that the calculated maximum ambient temperature is 114

°C at maximum power dissipation

with a 5-V supply and 4-

Ω a load. The TPA2012D2 is designed with thermal protection that turns the device off

when the junction temperature surpasses 150

°C to prevent damage to the IC. Also, using speakers more

resistive than 4-

Ω dramatically increases the thermal performance by reducing the output current and increasing

the efficiency of the amplifier.

In using Class-D amplifiers with CODECs and DACs, sometimes there is an increase in the output noise floor

from the audio amplifier. This occurs when mixing of the output frequencies of the CODEC/DAC mix with the

switching frequencies of the audio amplifier input stage. The noise increase can be solved by placing a low-pass

filter between the CODEC/DAC and audio amplifier. This filters off the high frequencies that cause the problem

and allow proper performance. See Figure 33 for the block diagram.

A ferrite bead filter can often be used if the design is failing radiated emissions without an LC filter and the

frequency sensitive circuit is greater than 1 MHz. This filter functions well for circuits that just have to pass FCC

and CE because FCC and CE only test radiated emissions greater than 30 MHz. When choosing a ferrite bead,

choose one with high impedance at high frequencies, and very low impedance at low frequencies. In addition,

select a ferrite bead with adequate current rating to prevent distortion of the output signal.

Use an LC output filter if there are low frequency (< 1 MHz) EMI sensitive circuits and/or there are long leads

from amplifier to speaker.

Figure 37 shows typical ferrite bead and LC output filters.

Figure 37. Typical Ferrite Chip Bead Filter (Chip bead example: TDK: MPZ1608S221A)

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