SLAU472C February 2013 – November 2023 TAS2505 , TAS2505-Q1
The DAC has a digital volume-control block which implements programmable gain. Each channel has an independent volume control that can be varied from 24 dB to –63.5 dB in 0.5-dB steps. The mono-channel DAC volume can be controlled by writing to page 0, register 65, bits D7–D0. DAC muting and setting up a master gain control to control the mono channel is done by writing to page 0, register 64, bits D3. The gain is implemented with a soft-stepping algorithm, which only changes the actual volume by 0.125 dB per input sample, either up or down, until the desired volume is reached. The rate of soft-stepping can be slowed to one step per two input samples by writing to page 0, register 63, bits D1–D0. Note that the default source for volume-control level settings is controlled by register writes to page 0, register 65.
During soft-stepping, the host does not receive a signal when the DAC has been completely muted. This may be important if the host must mute the DAC before making a significant change, such as changing sample rates. In order to help with this situation, the device provides a flag back to the host via a read-only register, page 0, register 38, bit D4 for the mono channel. This information alerts the host when the part has completed the soft-stepping, and the actual volume has reached the desired volume level. The soft-stepping feature can be disabled by writing to page 0, register 63, bits D1–D0.
If soft-stepping is enabled, the CODEC_CLKIN signal should be kept active until the DAC power-up flag is cleared. When this flag is cleared, the internal DAC soft-stepping process is complete, and CODEC_CLKIN can be stopped if desired. (The analog volume control can be ramped down using an internal oscillator.)