C

I

I

1

f =

(2

R

C )

p ´

´

(1)

I

I

C

1

C =

(2

R

f )

p ´

´

(2)

COMPONENT LOCATION

EFFICIENCY AND THERMAL INFORMATION

100°C/W

(3)

JA

DMAX

T

T

P

C

A

J

Max =

Max -

= 150 - 100 (0.4) = 110

q

°

(4)

OPERATION WITH DACS AND CODECS

TPA2017D2

The TPA2017D2 is a high-performance Class-D audio amplifier that requires adequate power supply decoupling

to ensure the efficiency is high and total harmonic distortion (THD) is low. For higher frequency transients,

spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) 1-

µF ceramic capacitor

(typically) placed as close as possible to the device PVDD (L, R) lead works best. Placing this decoupling

capacitor close to the TPA2017D2 is important for the efficiency of the Class-D amplifier, because any resistance

or inductance in the trace between the device and the capacitor can cause a loss in efficiency. For filtering

lower-frequency noise signals, a 4.7

µF or greater capacitor placed near the audio power amplifier would also

help, but it is not required in most applications because of the high PSRR of this device.

Equation 1.

The value of the input capacitor is important to consider as it directly affects the bass (low frequency)

performance of the circuit. Speakers in wireless phones cannot usually respond well to low frequencies, so the

corner frequency can be set to block low frequencies in this application. Not using input capacitors can increase

output offset. Equation 2 is used to solve for the input coupling capacitance. If the corner frequency is within the

audio band, the capacitors should have a tolerance of ±10% or better, because any mismatch in capacitance

causes an impedance mismatch at the corner frequency and below.

the TPA2017D2 is important for the efficiency of the Class-D amplifier. Any resistance or inductance in the trace

between the device and the capacitor can cause a loss in efficiency.

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 0.4 W (0.2 W per channel) for 1.5 W per channel, 8-

Ω load, 5-V supply, from Figure 9, the

maximum ambient temperature can be calculated with the following equation.

Equation 4 shows that the calculated maximum ambient temperature is 110°C at maximum power dissipation

with a 5-V supply and 8-

Ω a load. The TPA2017D2 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 8-

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 the functional block diagram.

12

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