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C

O

C

O

V

OUT

V

OUT

GND

GND

V

DD

V

DD

V

/2

DD

V

BIAS

Conventional

Capless

GND

V

DD

V

SS

V

BIAS

DirectPath

TM

Input-Blocking Capacitors

fc

1

2p R

C

1

2p fc

or

(3)

TPA4411

TPA4411M

SLOS430E – AUGUST 2004 – REVISED MARCH 2008

Figure 64. Amplifier Applications

The DirectPath™ amplifier architecture operates from a single supply but makes use of an internal charge pump

to provide a negative voltage rail. Combining the user provided positive rail and the negative rail generated by

the IC, the device operates in what is effectively a split supply mode. The output voltages are now centered at

zero volts with the capability to swing to the positive rail or negative rail. The DirectPath™ amplifier requires no

output dc blocking capacitors, and does not place any voltage on the sleeve. The bottom block diagram and

waveform of Figure 64 illustrate the ground-referenced headphone architecture. This is the architecture of the

TPA4411.

DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the

TPA4411 and TPA4411M. These capacitors block the DC portion of the audio source and allow the TPA4411

and TPA4411M inputs to be properly biased to provide maximum performance.

These capacitors form a high-pass filter with the input impedance of the TPA4411 and TPA4411M. The cutoff

frequency is calculated using Equation 3. For this calculation, the capacitance used is the input-blocking

capacitor and the resistance is the input impedance of the TPA4411 or TPA4411M. Because the gains of both

the TPA4411 and TPA4411M are fixed, the input impedance remains a constant value. Using the input

impedance value from the operating characteristics table, the frequency and/or capacitance can be determined

when one of the two values are given.

16

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