TPA152D datasheet(13/16 Pages) TI

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TPA152

75-mW STEREO AUDIO POWER AMPLIFIER

SLOS210A – JUNE 1998 – REVISED MARCH 2000

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

power supply decoupling, CS

The TPA152 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to

ensure that the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also

prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is

achieved by using two capacitors of different types that target different types of noise on the power supply leads.

For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance

(ESR) ceramic capacitor, typically 0.1

µF, placed as close as possible to the device VDD lead, works best. For

filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10

µF or greater placed near

the power amplifier is recommended.

midrail bypass capacitor, CB

The midrail bypass capacitor, CB, serves several important functions. During startup or recovery from shutdown

mode, CB determines the rate at which the amplifier starts up. This helps to push the start-up pop noise into

the subaudible range (so slow it can not be heard). The second function is to reduce noise produced by the

power supply caused by coupling into the output drive signal. This noise is from the midrail generation circuit

internal to the amplifier. The capacitor is fed from a 160-k

Ω source inside the amplifier. To keep the start-up pop

as low as possible, the relationship shown in equation 6 should be maintained.

(6)

160 k

Ω

I RI

As an example, consider a circuit where CB is 1 µF, CI is 1 µF and RI is 20 kΩ. Inserting these values into the

equation 9 results in:

6.25

v 50

which satisfies the rule. Bypass capacitor, CB, values of 0.1 µF to 1 µF ceramic or tantalum low-ESR capacitors

are recommended for the best THD and noise performance.

output coupling capacitor, CC

In the typical single-supply single-ended (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 7.

(7)

c(high) +

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

drive the low-frequency corner higher. Large values of CC are required to pass low frequencies into the load.

Consider the example where a CC of 68 µF is chosen and loads vary from 32 Ω to 47 kΩ. Table 1 summarizes

the frequency response characteristics of each configuration.

TPA152D Datasheet(PDF) 13 Page - Texas Instruments

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