TPA6203A1
SLOS364 – MARCH 2002
www.ti.com
12
Selecting Components
Resistors (RF and RI)
The input (RI) and feedback resistors (RF) set the gain of
the amplifier according to equation 1.
Gain = RF/RI
RF and RI should range from 1 k to 100 k. Most graphs
were taken with RF = RI = 20 k.
Resistor matching is very important in fully differential
amplifiers. The balance of the output on the reference
voltage depends on matched ratios of the resistors.
CMRR, PSRR, and the cancellation of the second
harmonic distortion diminishes if resistor mismatch
occurs. Therefore, it is recommended to use 1% tolerance
resistors or better to keep the performance optimized.
Bypass Capacitor (CBYPASS) and Start-Up Time
The internal voltage divider at the BYPASS pin of this
device sets a mid-supply voltage for internal references
and sets the output common mode voltage to VDD/2.
Adding a capacitor to this pin filters any noise into this pin
and increases the kSVR. C(BYPASS) also determines the
rise time of VO+ and VO– when the device is taken out of
shutdown. The larger the capacitor, the slower the rise
time. Although the output rise time depends on the bypass
capacitor value, the device passes audio 4
s after taken
out of shutdown and the gain is slowly ramped up based
on C(BYPASS).
Input Capacitor (CI)
The TPA6203A1 does not require input coupling
capacitors if using a differential input source that is biased
from 0.5 V to VDD – 0.8 V. Use 1% tolerance or better
gain-setting resistors if not using input coupling capacitors.
In the single-ended input application an input capacitor, CI,
is required to allow the amplifier to bias the input signal to
the proper dc level. In this case, CI and RI form a high-pass
filter with the corner frequency determined in equation 2.
fc +
1
2
pR
I
C
I
–3 dB
fc
The value of CI is important to consider as it directly affects
the bass (low frequency) performance of the circuit.
Consider the example where RI is 10 k and the
specification calls for a flat bass response down to 100 Hz.
Equation 2 is reconfigured as equation 3.
C
I +
1
2
pR
I
fc
In this example, CI is 0.16 F, so one would likely choose
a value in the range of 0.22
F to 0.47 F. A further
consideration for this capacitor is the leakage path from
the input source through the input network (RI, CI) and the
feedback resistor (RF) to the load. This leakage current
creates a dc offset voltage at the input to the amplifier that
reduces useful headroom, especially in high gain
applications. For this reason, a 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
VDD/2, which is likely higher than the source dc level. It is
important to confirm the capacitor polarity in the
application.
Decoupling Capacitor (CS)
The TPA6203A1 is a high-performance CMOS audio
amplifier that requires adequate power supply decoupling
to ensure 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. For higher frequency transients, spikes, or
digital hash on the line, a good low equivalent-series-
resistance (ESR) ceramic capacitor, typically 0.1
F to
1
F, placed as close as possible to the device VDD lead
works best. For filtering lower frequency noise signals, a
10-
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.
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.
DIFFERENTIAL OUTPUT VERSUS SINGLE-
ENDED OUTPUT
Figure 32 shows a Class-AB audio power amplifier (APA)
in a fully differential configuration. The 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 drive to the speaker means that as one side
(1)
(2)
(3)