In applications like karaoke, where overlaying voice while music is streamed, mixing the external analog microphone input with the stored and recorded digital input is required. The mixed output needs to be played on the analog output of the DAC.

The TAD5212 supports mixing the DAC output with external analog inputs as well as routing external analog signals to the output.

In Figure 2-9, there are two independent paths to the output of the chip. One path is the output of the DAC that is connected through the buffers to output pins. The second path can be connected to external analog inputs.

The TAD5212 supports multiple data mixing options with up to eight input channels from Main ASI, two Input Channels from Aux ASI, and a tone generator that can be mixed with flexible gain options for each path before playback on DAC output. By default, these mixers are disabled and channels are configured for only one channel data. Table 2-3 summarizes the DAC defaults and configurations of the mixer. In Stereo Single Ended mode (SSE) the device can support up to four independent single-ended outputs. SSE is configured through OUT1x_CFG (B0_P0_R100_D[4:2]) and OUT2x_CFG (B0_P0_R107_D[4:2])

Mixers can be configured by setting ASI_DIN_Mixers in Page 17 of register map. If the DAC and analog input are both enabled, the user must verify that the combination of analog bypass and digital DAC signal chain does not cross the full scale value. There are independent gain knobs for the digital DAC signal chain (Book0, Page 0_Rregister 103 and 110) that can be adjusted as long as the end output is not beyond full scale.

A feature of the TAD5212 is the ability to bypass the DAC and send an analog input signal directly to the DAC output. This feature is accessed by using register 100 (0h64) and register 107 (0h6B) for VOUT1x and VOUT2x, respectively. If the output signal needs to be received from OUTP, then the analog signal needs to be applied at INM input and due to the negative feedback connection, the output signal is the inverted version of the input signal.

The input impedance of the analog input for single-ended use-cases has the option for 4.4kΩ or 20kΩ impedance. For fully-differential configurations, the options are 8.8kΩ or 40kΩ.

In Figure 2-9, the switches in the analog input signal path close, while the switches in the DAC output open up to route the analog signal to the output buffers and then to the output pins.

The OUT1x_CFG0 register (Address = 0x64) can be used for different configuration to direct the DAC and analog inputs to OUT2P and OUT2M. Similarly, the OUT2x_CFG0 register (Address = 0x6B) can be used for different configurations to direct the DAC and analog inputs to OUT2P and OUT2M.

As an example, the device can be programed to route the input from the DAC signal chain or the input from the analog bypass path to the DAC outputs. Similarly the device can independently route the DAC output to OUT2P, IN2P to OUT2M, the DAC output to OUT2M, or the analog input at IN2M to OUT2P, among many other options, including disabling output drivers. Table 2-4 summarizes the variety of options to route the analog or DAC output to the output pins.

The TAD5212 supports ±100mV common-mode voltage on the analog pins in bypass mode. In pseudo-differential configuration, the input and the common-mode voltage need to be applied to ANA_P and ANA_M, respectively, to get the output at OUT1P. This same rule applies to OUT2P, when the other channel is being used.