OPAMP

Co

MuteCircuit

Output

MUTE

9-12 V

+

+

+

-

ConventionalSolution

DRV604

MuteCircuit

Output

MUTE

3.3V

+

-

DRV604Solution

VDD

VSS

GND

VDD

VDD/2

GND

DirectPath

DRV604

www.ti.com

SLOS659 – JANUARY 2010

APPLICATION INFORMATION

LINE DRIVER AMPLIFIERS

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

Figure 13 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 13. 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 build in click and pop reduction circuit, the DirectPath™ amplifier requires no output dc

blocking capacitors.

The bottom block diagram and waveform of Figure 13 illustrate the ground-referenced headphone and line driver

architecture. This is the architecture of the DRV604.

COMPONENT SELECTION

Charge Pump

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

The PVSS capacitor 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 1µF is typical. Capacitor values that are

smaller than 1µF can not be recommended for the HP section as it will limit the negative voltage swing in low

impedance loads.

Copyright © 2010, Texas Instruments Incorporated

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Product Folder Link(s) :DRV604