R
in
R
fb
+
–
C
in
–In
S0446-01
in
1
fc
=
C
=
2
R
C
2
fc
R
p
SLOS655A
– NOVEMBER 2010 – REVISED FEBRUARY 2011
Decoupling Capacitors
The TAS5717/9 is a DirectPath
amplifier that requires adequate power supply decoupling to ensure that the
noise and total harmonic distortion (THD) are low. A good low equivalent-series-resistance (ESR) ceramic
capacitor, typically 1
F, placed as close as possible to the device PVDD leads works best. Placing this
decoupling capacitor close to the TAS5717/9 is important for the performance of the amplifier. For filtering lower
frequency noise signals, a 10
F or greater capacitor placed near the audio power amplifier would also help, but it
is not required in most applications because of the high PSRR of this device.
Gain Setting Resistors Ranges
The gain setting resistors, Rin and Rfb, must be chosen so that noise, stability and input capacitor size of the
TAS5717/9 is kept within acceptable limits. Voltage gain is defined as Rfb divided by Rin. Selecting values that
are too low demands a large input ac-coupling capacitor, CIN. Selecting values that are too high increases the
noise of the amplifier.
Table 25 lists the recommended resistor values for different gain settings.
Table 25. Recommended Resistor Values
INPUT RESISTOR
FEEDBACK RESISTOR
DIFFERENTIAL
INVERTING INPUT
NON INVERTING
VALUE, Rin
VALUE, Rfb
INPUT GAIN
GAIN
INPUT GAIN
10 k
Ω
10 k
Ω
1.0 V/V
–1.0 V/V
2.0 V/V
10 k
Ω
15 k
Ω
1.5 V/V
–1.5 V/V
2.5 V/V
10 k
Ω
20 k
Ω
2.0 V/V
–2.0 V/V
3.0 V/V
4.7 k
Ω
47 k
Ω
10.0 V/V
–10.0 V/V
11.0 V/V
Figure 48. Inverting Gain Configuration
Input-Blocking Capacitors
DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the
TAS5717/9. These capacitors block the DC portion of the audio source and allow the TAS5717/9 inputs to be
properly biased to provide maximum performance. The input blocking capacitors also limit the DC gain to 1,
limiting the DC-offset voltage at the output.
These capacitors form a high-pass filter with the input resistor, Rin. The cutoff frequency is calculated using
Equation 1. For this calculation, the capacitance used is the input-blocking capacitor and the resistance is the
input resistor chosen from
Table 25, then the frequency and/or capacitance can be determined when one of the
two values is given.
(1)
Using the TAS5717/9 as a 2nd order filter
Several audio DACs used today require an external low-pass filter to remove out of band noise. This is possible
with the TAS5717/9 as it can be used like a standard OPAMP. Several filter topologies can be implemented both
single ended and differential. In the figure below a Multi Feed Back (MFB), with differential input and single
ended input is shown.
An AC-coupling capacitor to remove dc-content from the source is shown, it serves to block any dc content from
the source and lowers the dc-gain to 1 helping reducing the output dc-offset to minimum.
58
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