The TAC5412-Q1 consists of two pairs of analog input pins (INxP and INxM) that can be configured as either differential or single-ended inputs for the recording channel. The device supports simultaneous recording of up to two channels using the multichannel ADC. The input source for the analog pins can be either analog microphones or line, aux inputs from the system board. Table 6-8 describes how to set the input configuration for the record channel.

Similarly, the input source selection setting for input channel 2 can be configured using the ADC_CH2_INSRC[1:0] (P0_R85_D[7:6]) register bits.

The device supports the input DC fault diagnostic feature for microphone recording with the DC-coupled inputs configuration; however, the device also supports an option for AC-coupled inputs if the DC diagnostic is not required for the specific input pins.

For the DC-coupled line input configuration, the DC common-mode difference (INxP – INxM) for the analog input pins must be 0V to support the 10-V_RMS full-scale differential input. For the DC-coupled microphone input configuration, the DC common-mode difference (INxP – INxM) for the analog input pins must be within 3.4V to 6.0V to support the 2-V_RMS full-scale differential input in the default mode of operation. The DC differential common-mode voltage is later filtered out by the digital high-pass filter and the digital output full-scale corresponds to the 10V_RMS AC signal in this case.

Figure 6-15 and Figure 6-16 show how to connect a DC-coupled microphone for a differential and single-ended input, respectively. The value of the external bias resistor, R1, must be appropriately chosen based upon the microphone impedance. For a differential input, the value of the external bias resistor is recommended to be used for half of the microphone impedance, whereas for a single-ended input, the external bias resistor is recommended to be the same as the microphone impedance.

Figure 6-15 DC-Coupled Microphone Differential Input Connection

Figure 6-16 DC-Coupled Microphone Single-Ended Input Connection

In AC-coupled mode, the value of the coupling capacitor must be so chosen that the high-pass filter formed by the coupling capacitor and the input impedance do not affect the signal content. At power-up, before proper recording can begin, this coupling capacitor must be charged up to the common-mode voltage. For single-ended input configuration, the INxM pin must be grounded after the AC coupling capacitor in AC-coupled mode.

Figure 6-17 and Figure 6-18 show how to connect an AC-coupled microphone or line source for a differential and single-ended input, respectively. In AC-coupled mode, the device input pins INxP and INxM, must be biased appropriately for the DC common-mode value either using the on-chip MICBIAS output voltage along with external bias resistor, R0, or using an external bias generator circuit. The maximum value for resistor R0 depends upon the signal swing and the MICBIAS value programmed. See the TAC5xxx-Q1 AC Coupled External Resistor Calculator to calculate the R0 value for the desired system configuration.

Figure 6-17 AC-Coupled Microphone or Line Differential Input Connection

Figure 6-18 AC-Coupled Microphone or Line Single-Ended Input Connection