Datasheet

1
ǒ
C
(B)
230 kΩ
Ǔ
v
1
ǒ
C
i
R
i
Ǔ
1
ǒ
C
(B)
230 kΩ
Ǔ
v
1
ǒ
C
i
R
i
Ǔ
Ơ
1
R
L
C
(C)
f
c
+
1
2p R
L
C
(C)
TPA6110A2
www.ti.com SLOS314B –DECEMBER 2000– REVISED MARCH 2011
Table 1. Common Load Impedances vs Low-
MIDRAIL BYPASS CAPACITOR, C
(B)
Frequency Output Characteristics in SE Mode
The midrail bypass capacitor, C
(B)
, serves several
R
L
C
(C)
LOWEST FREQUENCY
important functions. During start up, C
(B)
determines
32 Ω 68 µF 73 Hz
the rate at which the amplifier starts up. This helps to
push the start-up pop noise into the subaudible range
10,000 Ω 68 µF 0.23 Hz
(so low it can not be heard). The second function is to
47,000 Ω 68 µF 0.05 Hz
reduce noise produced by the power supply caused
by coupling into the output drive signal. This noise is
As Table 1 indicates, headphone response is
from the midrail generation circuit internal to the
adequate, and drive into line level inputs (a home
amplifier. The capacitor is fed from a 230-kΩ source
stereo for example) is very good.
inside the amplifier. To keep the start-up pop as low
The output coupling capacitor required in
as possible, maintain the relationship shown in
single-supply SE mode also places additional
Equation 6.
constraints on the selection of other components in
the amplifier circuit. With the rules described earlier
still valid, add the following relationship:
(6)
Consider an example circuit where C
(B)
is 1 µF, C
i
is
1 µF, and R
i
is 20 kΩ. Subsitituting these values into
(8)
the equation 9 results in: 6.25 ≤ 50 which satisfies the
rule. Bypass capacitor, C
(B)
, values of 0.1 µF to 1 µF
USING LOW-ESR CAPACITORS
ceramic or tantalum low-ESR capacitors are
Low-ESR capacitors are recommended throughout
recommended for the best THD and noise
this application. A real capacitor can be modeled
performance.
simply as a resistor in series with an ideal capacitor.
The voltage drop across this resistor minimizes the
OUTPUT COUPLING CAPACITOR, C
(C)
beneficial effects of the capacitor in the circuit. The
In a typical single-supply, single-ended (SE)
lower the equivalent value of this resistance, the
configuration, an output coupling capacitor (C
(C)
) is
more the real capacitor behaves like an ideal
required to block the dc bias at the output of the
capacitor.
amplifier, thus preventing dc currents in the load. As
with the input coupling capacitor, the output coupling
5-V VERSUS 3.3-V OPERATION
capacitor and impedance of the load form a
The TPA6110A2 was designed for operation over a
high-pass filter governed by Equation 7.
supply range of 2.5 V to 5.5 V. This data sheet
provides full specifications for 5-V and 3.3-V
operation, since these are considered to be the two
most common supply voltages. There are no special
(7)
considerations for 3.3-V versus 5-V operation as far
as supply bypassing, gain setting, or stability. The
The main disadvantage, from a performance
most important consideration is that of output power.
standpoint, is that the typically-small load impedance
Each amplifier in theTPA6110A2 can produce a
drives the low-frequency corner higher. Large values
maximum voltage swing of V
DD
– 1 V. This means,
of C
(C)
are required to pass low frequencies into the
for 3.3-V operation, clipping starts to occur when
load. Consider the example where a C
(C)
of 68 µF is
V
O(PP)
= 2.3 V as opposed when V
O(PP)
= 4 V while
chosen and loads vary from 32 Ω to 47 kΩ. Table 1
operating at 5 V. The reduced voltage swing
summarizes the frequency response characteristics
subsequently reduces maximum output power into
of each configuration.
the load before distortion becomes significant.
Copyright © 2000–2011, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Link(s): TPA6110A2