TAS5721 datasheet(63/71 Pages) TI1

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S0446-01

TAS5721

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SLOS739 – JULY 2012

Decoupling Capacitors

The TAS5721 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 µF, placed as close as possible to the device PVDD leads works best. Placing this decoupling

capacitor close to the TAS5721 is important for the performance of the amplifier. For filtering lower frequency

noise signals, a 10µF 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. Please refer to the TAS5721 for the

recommended layout for these components.

Gain Setting Resistors Ranges

The gain setting resistors, Rin and Rfb, must be chosen so that noise, stability and input capacitor size of the

TAS5721 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 24 lists the recommended resistor values for different gain settings.

Table 24. Recommended Resistor Values

INPUT RESISTOR

FEEDBACK RESISTOR

DIFFERENTIAL

INVERTING INPUT

NON INVERTING

VALUE, Rin

VALUE, Rfb

INPUT GAIN

GAIN

INPUT GAIN

10 k

1 V/V

–1 V/V

2 V/V

10 k

15 k

1.5 V/V

–1.5 V/V

2.5 V/V

10 k

20 k

2 V/V

–2 V/V

3 V/V

4.7 k

47 k

10 V/V

–10 V/V

11 V/V

Figure 75. 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

TAS5721. These capacitors block the DC portion of the audio source and allow the TAS5721 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 24, then the frequency and/or capacitance can be determined when one of the

two values is given.

(1)

Using the TAS5721 as a Second Order Filter

Several audio DACs used today require an external low-pass filter to remove out of band noise. This is possible

with the TAS5721 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 reduce the output dc-offset to a minimum.

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