TAS5721 datasheet(62/71 Pages) TI1

62 / 71 page

OPAMP

Mute Circuit

Output

MUTE

9–12 V

–

Conventional Solution

Mute Circuit

Output

DR_SD

3.3 V

–

TAS5721 Solution

VDD

VSS

GND

VDD

VDD/2

GND

DirectPath

TAS5721

SLOS739 – JULY 2012

www.ti.com

USING LINE DRIVER AMPLIFIER IN TAS5721

Single-supply headphone and line driver amplifiers typically require dc-blocking capacitors. The top drawing in

Figure 74 illustrates the conventional line driver amplifier connection to the load and output signal.

DC blocking capacitors for headphone amps are often large in value, and a mute circuit is needed during power

up to minimize click and pop for both headphone and line driver. The output capacitors and mute circuits

consume PCB area and increase cost of assembly, and can reduce the fidelity of the audio output signal.

Figure 74. Conventional and DirectPath HP and Line Driver

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,

combining this with the built in click and pop reduction circuit, the DirectPath amplifier requires no output dc

blocking capacitors.

The bottom block diagram and waveform of Figure 74 illustrate the ground-referenced headphone and line driver

architecture. This is the architecture of the TAS5721.

COMPONENT SELECTION

Charge Pump

The charge pump flying capacitor serves to transfer charge during the generation of the negative supply voltage.

The capacitor connected to the DR_VSS pin must be at least equal to the charge pump capacitor in order to

allow maximum charge transfer. Low ESR capacitors are an ideal selection, and a value of 1 µF is typical.

Capacitor values that are smaller than 1 µF are not recommended for the DR_VSS pin as they will limit the

negative voltage swing when driving low impedance loads.

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