Datasheet

R
L
2x V
O(PP)
V
O(PP)
-V
O(PP)
V
DD
V
DD
f
c
+
1
2p R
L
C
C
V
(rms)
+
V
O(PP)
2 2
Ǹ
Power +
V
(rms)
2
R
L
TPA6211A1
www.ti.com SLOS367D –AUGUST 2003– REVISED JUNE 2011
lengths between the amplifier and the speaker. For
higher frequency transients, spikes, or digital hash on
the line, a good low equivalent-series-resistance
(ESR) ceramic capacitor, typically 0.1 μF to 1 μF,
placed as close as possible to the device V
DD
lead
works best. For filtering lower frequency noise
signals, a 10-μF or greater capacitor placed near the
audio power amplifier also helps, but is not required
in most applications because of the high PSRR of this
device.
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
Figure 33. Differential Output Configuration
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
In a typical wireless handset operating at 3.6 V,
value of this resistance the more the real capacitor
bridging raises the power into an 8-Ω speaker from a
behaves like an ideal capacitor.
singled-ended (SE, ground reference) limit of 200
mW to 800 mW. This is a 6-dB improvement in sound
DIFFERENTIAL OUTPUT VERSUS
power—loudness that can be heard. In addition to
SINGLE-ENDED OUTPUT
increased power, there are frequency-response
concerns. Consider the single-supply SE
Figure 33 shows a Class-AB audio power amplifier
configuration shown in Figure 34. A coupling
(APA) in a fully differential configuration. The
capacitor (C
C
) is required to block the dc-offset
TPA6211A1 amplifier has differential outputs driving
voltage from the load. This capacitor can be quite
both ends of the load. One of several potential
large (approximately 33 μF to 1000 μF) so it tends to
benefits to this configuration is power to the load. The
be expensive, heavy, occupy valuable PCB area, and
differential drive to the speaker means that as one
have the additional drawback of limiting
side is slewing up, the other side is slewing down,
low-frequency performance. This frequency-limiting
and vice versa. This in effect doubles the voltage
effect is due to the high-pass filter network created
swing on the load as compared to a
with the speaker impedance and the coupling
ground-referenced load. Plugging 2 × V
O(PP)
into the
capacitance. This is calculated with Equation 13.
power equation, where voltage is squared, yields 4×
the output power from the same supply rail and load
impedance Equation 12.
(13)
(12)
Copyright © 2003–2011, Texas Instruments Incorporated 17