DRV600_15 Datasheet, PDF (7/17 Pages) Texas Instruments – DIRECTPATH™ STEREO LINE DRIVER

DRV600
www.ti.com
APPLICATION INFORMATION
SLOS536 – JUNE 2007
Line Driver Amplifiers
Single-supply 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 are often large in value. The line load (typical resistive values of 600 Ω to 10 kΩ)
combine 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).
f_c
=
1
2pR_LC_O
(1)
C_O can be determined using Equation 2, where the load impedance and the cutoff frequency are known.
C_O =
1
2pR_Lf_c
(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.
Conventional
C_O
V_DD
V_OUT
V_DD/2
C_O
GND
DirectPath
V_DD
GND
V_SS
Figure 13. Amplifier Applications
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. The DirectPath™ amplifier requires no
output dc blocking capacitors. The bottom block diagram and waveform of Figure 13 illustrate the
ground-referenced Line Driver architecture. This is the architecture of the DRV600.
Input-Blocking Capacitors
DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the
DRV600. These capacitors block the DC portion of the audio source and allow the DRV600 inputs to be properly
biased to provide maximum performance.
These capacitors form a high-pass filter with the input impedance of the DRV600. The cutoff frequency is
calculated using Equation 3. For this calculation, the capacitance used is the input-blocking capacitor and the
resistance is the input impedance of the DRV600. Because the gain of the DRV600 is fixed, the input
impedance remains a constant value. Using the input impedance value from the operating characteristics table,
the frequency and/or capacitance can be determined when one of the two values are given.
fc_IN
+
2p
1
R_IN
C_IN
or
C_IN
+
2p
1
fc_IN
R_IN
(3)
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