OPAMP

Co

Mute Circuit

Output

Enable

+

+

+

–

Conventional Solution

DRV632

Mute Circuit

Output

Enable

3.3 V

+

–

DRV632 Solution

VDD

VSS

GND

VDD

VDD/2

GND

DirectPath

9 V–12 V

O

L c

1

C

=

2 R f

p

c

L

O

1

f =

2 R C

p

9

DRV632

www.ti.com

SLOS681C – JANUARY 2011 – REVISED AUGUST 2019

Product Folder Links: DRV632

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Copyright © 2011–2019, Texas Instruments Incorporated

9.3 Feature Description

9.3.1 Line Driver Amplifiers

Single-supply line-driver amplifiers typically require dc-blocking capacitors. The top drawing in Figure 6 illustrates

the conventional line-driver amplifier connection to the load and output signal. DC blocking capacitors are often

large in value. The line load (typical resistive values of 600 Ω to 10 kΩ) combines with the dc blocking capacitors

to form a high-pass filter. Equation 1 shows the relationship between the load impedance (RL), the capacitor

(CO), and the cutoff frequency (fC).

(1)

CO can be determined using Equation 2, where the load impedance and the cutoff frequency are known.

(2)

If fC is low, the capacitor must then have a large value because the load resistance is small. Large capacitance

values require large package sizes. Large package sizes consume PCB area, stand high above the PCB,

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

Figure 6. Conventional and DirectPath Line Drivers

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 6 illustrate the ground-referenced line-driver architecture. This is the architecture of the

DRV632.

9.3.2 Charge-Pump Flying Capacitor and PVSS Capacitor

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 1 μF is typical. Capacitor values that are

smaller than 1 μF can be used, but the maximum output voltage may be reduced and the device may not operate

to specifications. If the DRV632 is used in highly noise-sensitive circuits, TI recommends adding a small LC filter

on the VDD connection.