SLASEM6C October 2017 – October 2020 TAS2770
The gain from audio input to speaker terminals is controlled by setting the amplifier’s output level and digital volume control (DVC). A separate DVC is provided for PDM (available from the PDM input pins) and PCM (available from the TDM ports pins) playback paths.
Amplifier output level settings are presented in dBV (dB relative to 1 Vrms) with a full scale digital audio input (0 dBFS) and the digital volume control set to 0 dB. It should be noted that these levels may not be achievable because of analog clipping in the amplifier, so they should be used to convey gain only. Table 8-37 below shows analog gain settings that can be programmed via the AMP_LEVEL[4:0] register bits.
|AMP_LEVEL[4:0]||FULL SCALE OUTPUT|
|19.0 (default)||12.6 (default)|
Equation 1 calculates the amplifiers output voltage.
The digital volume control (DVC) is independently configurable for PCM and PDM streams from 0 dB to -100 dB in 0.5 dB steps by setting the DVC_PCM[7:0] and PVC_PDM[7:0] register bits respectively. Settings greater than 0xC8 are interpreted as mute. When a change in digital volume control occurs, the device ramps the volume to the new setting based on the DVC_RATE[1:0] register bits. If DVC_RATE[1:0] is set to 2'b11, volume ramping is disabled. This can be used to speed up startup, shutdown and digital volume changes when volume ramping is handled by the system master.
|0.5 dB per 1 Sample (default)|
|0.5 dB per 4 Samples|
|0.5 dB per 8 Samples|
|Volume Ramping Disabled|
The Class-D amplifier uses a closed-loop architecture, so the gain does not depend on VBAT. The approximate threshold for the onset of analog clipping is calculated in Equation 2.
The effective on-resistance for this device (including HS+LS FET, Sense Resistor and bonding and packaging leads) is approximately 510 mΩ at room temperature. Table 8-41 shows approximate maximum unclipped peak output voltages at room temperature (excluding interconnect resistances).
|RL = 4 Ω||RL = 8 Ω|