ZHCSBA9C July 2013 – November 2017 TAS5760LD
PRODUCTION DATA.
Single-supply line-driver amplifiers typically require dc-blocking capacitors. The top drawing in Figure 58 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 3 shows the relationship between the load impedance (RL), the capacitor (CO), and the cutoff frequency (fC).
CO can be determined using Equation 4, where the load impedance and the cutoff frequency are known.
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.
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 58 illustrate the ground-referenced line-driver architecture. This is the architecture of the headphone / line driver inside of the TAS5760LD.