DRV604 Datasheet, PDF (9/21 Pages) Texas Instruments – DirectPath™ 2Vrms Line Driver and HP Amp With Adjustable Gain

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DRV604
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.
9-12 V
Conventional Solution
+
+
Co
OPAMP
+
-
Mute Circuit
Output
GND
VDD
VDD/2
MUTE
3.3 V
+
DRV604
-
DRV604 Solution
Mute Circuit
Output
DirectPath
VDD
GND
VSS
MUTE
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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