TPA0252 Datasheet, PDF (20/29 Pages) Texas Instruments – 2.8-W STEREO AUDIO POWER AMPLIFIER WITH DIGITAL VOLUME CONTROL

TPA0252
SLOS288B – JUNE 2000 – REVISED SEPTEMBER 2004
www.ti.com
As Table 1 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.
USING LOW-ESR CAPACITORS
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.
BRIDGED-TIED LOAD VS SINGLE-ENDED MODE
Figure 36 shows a Class-AB audio power amplifier (APA) in a BTL configuration. The TPA0252 amplifier consists
of two Class-AB amplifiers driving both ends of the load. There are several potential benefits to this differential
drive configuration, but, initially consider power to the load. The differential drive to the speaker means that as
one side is slewing up, the other side is slewing down, and vice versa. This in effect doubles the voltage swing
on the load as compared to a ground referenced load. Substituting 2 × V_O(PP) into the power equation, where
voltage is squared, yields 4× the output power from the same supply rail and load impedance (see Equation 6).
V_(rms)
+
V_O(PP)
2 ^Ǹ2
Power
+
V_(rms)2
R_L
(6)
V_DD
V_O(PP)
R_L
V_DD
2x V_O(PP)
−V_O(PP)
Figure 36. Bridge-Tied Load Configuration
In a typical computer sound channel operating at 5 V, bridging raises the power into an 8-Ω speaker from a
singled-ended (SE, ground reference) limit of 250 mW to 1 W. In sound power, this is a 6-dB improvement —
loudness that can be heard. In addition to increased power there are frequency-response concerns. Consider the
single-supply SE configuration shown in Figure 37. A coupling capacitor is required to block the dc offset voltage
from reaching the load. These capacitors can be quite large (approximately 33 µF to 1000 µF), so they tend to be
expensive, heavy, occupy valuable PCB area, and have the additional drawback of limiting the low-frequency
performance of the system. This frequency-limiting effect is due to the high-pass filter network created with the
speaker impedance and the coupling capacitance, and is calculated with Equation 7.
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