DRV632_15 Datasheet, PDF (9/23 Pages) Texas Instruments – DRV632 DirectPath™, 2-VRMS Audio Line Driver With Adjustable Gain

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DRV632
SLOS681B – JANUARY 2011 – REVISED AUGUST 2015
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 (R_L), the capacitor
(C_O), and the cutoff frequency (f_C).
1
f_c = _{2p RLCO}
(1)
C_O can be determined using Equation 2, where the load impedance and the cutoff frequency are known.
1
C_O = _{2p RLfc}
(2)
If f_C 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.
9 V–12 V
+
+
Co
OPAMP
+
–
Conventional Solution
Mute Circuit
Output
GND
VDD
VDD/2
Enable
3.3 V
+
DRV632
–
DRV632 Solution
Mute Circuit
Output
DirectPath
VDD
GND
VSS
Enable
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.
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