Datasheet

Input Capacitor (C
I
) Decoupling Capacitor (C
S
)
f
c
+
1
2pR
I
C
I
(2)
USING LOW-ESR CAPACITORS
–3 dB
f
c
DIFFERENTIAL OUTPUT VERSUS
C
I
+
1
2pR
I
f
c
(3)
TPA6203A1
www.ti.com .......................................................................................................................................................... SLOS364F – MARCH 2002 – REVISED JUNE 2008
The TPA6203A1 does not require input coupling The TPA6203A1 is a high-performance CMOS audio
capacitors if using a differential input source that is amplifier that requires adequate power supply
biased from 0.5 V to V
DD
- 0.8 V. Use 1% tolerance decoupling to ensure the output total harmonic
or better gain-setting resistors if not using input distortion (THD) is as low as possible. Power supply
coupling capacitors. decoupling also prevents oscillations for long lead
lengths between the amplifier and the speaker. For
In the single-ended input application an input
higher frequency transients, spikes, or digital hash on
capacitor, C
I
, is required to allow the amplifier to bias
the line, a good low equivalent-series- resistance
the input signal to the proper dc level. In this case, C
I
(ESR) ceramic capacitor, typically 0.1 µ F to 1 µ F,
and R
I
form a high-pass filter with the corner
placed as close as possible to the device V
DD
lead
frequency determined in Equation 2 .
works best. For filtering lower frequency noise
signals, a 10- µ F 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.
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.
The value of C
I
is important to consider as it directly
affects the bass (low frequency) performance of the
SINGLE-ENDED OUTPUT
circuit. Consider the example where R
I
is 10 k Ω and
Figure 31 shows a Class-AB audio power amplifier
the specification calls for a flat bass response down
(APA) in a fully differential configuration. The
to 100 Hz. Equation 2 is reconfigured as Equation 3 .
TPA6203A1 amplifier has differential outputs 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
In this example, C
I
is 0.16 µ F, so one would likely
drive to the speaker means that as one side is
choose a value in the range of 0.22 µ F to 0.47 µ F. A
slewing up, the other side is slewing down, and vice
further consideration for this capacitor is the leakage
versa. This in effect doubles the voltage swing on the
path from the input source through the input network
load as compared to a ground referenced load.
(R
I
, C
I
) and the feedback resistor (R
F
) to the load.
Plugging 2 × V
O(PP)
into the power equation, where
This leakage current creates a dc offset voltage at the
voltage is squared, yields 4 × the output power from
input to the amplifier that reduces useful headroom,
the same supply rail and load impedance (see
especially in high gain applications. For this reason, a
Equation 4 ).
ceramic capacitor is the best choice. When polarized
capacitors are used, the positive side of the capacitor
should face the amplifier input in most applications,
as the dc level there is held at V
DD
/2, which is likely
higher than the source dc level. It is important to
confirm the capacitor polarity in the application.
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