TPA0312 datasheet(21/32 Pages) TI

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OUTPUT COUPLING CAPACITOR, C

c(high) +

2 p R

−3 dB

(4)

USING LOW-ESR CAPACITORS

TPA0312

SLOS335A – DECEMBER 2000 – REVISED OCTOBER 2004

In the typical single-supply SE configuration, an output coupling capacitor (CC) is required to block the dc bias at

the output of the amplifier thus preventing dc currents in the load. As with the input coupling capacitor, the output

coupling capacitor and impedance of the load form a high-pass filter governed by Equation 4.

The main disadvantage, from a performance standpoint, is the load impedances are typically small, which drives

the low-frequency corner higher, degrading the bass response. Large values of CC are required to pass low

frequencies into the load. Consider the example where a CC of 330 µF is chosen and loads vary from 3 Ω, 4 Ω,

Ω, 32 Ω, 10 kΩ, to 47 kΩ. Table 2 summarizes the frequency response characteristics of each configuration.

Table 2. COMMON LOAD IMPEDANCES VS LOW FREQUENCY OUTPUT CHARACTERISTICS IN SE MODE

RL (Ω)

CC (µF)

LOWEST FREQUENCY( Hz)

330

161

330

120

330

10,000

330

0.05

47,000

330

0.01

As Table 2 indicates, most of the bass response is attenuated into a 4-

Ω load, an 8-Ω load is adequate,

headphone response is good, and drive into line level inputs (a home stereo, for example) is exceptional.

Low-ESR capacitors are recommended throughout this applications section. A real (as opposed to ideal)

capacitor can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this

resistor minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this

resistance, the more the real capacitor behaves like an ideal capacitor.

TPA0312 Datasheet(PDF) 21 Page - Texas Instruments