8.1.1 Connection Diagrams

A basic connection diagram is shown in Figure 39, with the necessary power-supply bypassing and decoupling components. Texas Instruments’ PLL170X is used to generate the system clock input at SCKI, as well as to generate the clock for the audio signal processor. The use of series resistors (22 Ω to 100 Ω) are recommended for SCKI, LRCK, BCK, and DIN for electromagnetic interference (EMI) reduction.

8.1.2 Power Supply and Grounding

The PCM1789 requires +5 V for the analog supply and +3.3 V for the digital supply. The +5-V supply is used to power the DAC analog and output filter circuitry, and the +3.3-V supply is used to power the digital filter and serial interface circuitry. For best performance, it is recommended to use a linear regulator (such as the REG101-5/33, REG102-5/33, or REG103-5/33) with the +5-V and +3.3-V supplies.

Five capacitors are required for supply bypassing, as shown in Figure 39. These capacitors should be located as close as possible to the PCM1789 package. The 10-μF capacitors are aluminum electrolytic, while the three 1-μF capacitors are ceramic.

8.1.3 Low-Pass Filter and Differential-to-Single-Ended Converter For DAC Outputs

ΔΣ DACs use noise-shaping techniques to improve in-band signal-to-noise ratio (SNR) performance at the expense of generating increased out-of-band noise above the Nyquist frequency, or f_S/2. The out-of-band noise must be low-pass filtered in order to provide optimal converter performance. This filtering is accomplished by a combination of on-chip and external low-pass filters.

Figure 37 and Figure 38 show the recommended external differential-to-single-ended converter with low-pass active filter circuits for ac-coupled and dc-coupled applications. These circuits are second-order Butterworth filters using a multiple feedback (MFB) circuit arrangement that reduces sensitivity to passive component variations over frequency and temperature. For more information regarding MFB active filter designs, please refer to Applications Bulletin SBAA055, Dynamic Performance Testing of Digital Audio D/A Converters, available from the TI web site (www.ti.com) or your local Texas Instruments' sales office.

Because the overall system performance is defined by the quality of the DACs and the associated analog output circuitry, high-quality audio op amps are recommended for the active filters. Texas Instruments’ OPA2134, OPA2353, and NE5532A dual op amps are shown in Figure 37 and Figure 38, and are recommended for use with the PCM1789.

NOTE: Amplifier is an NE5532A x 1/2 or OPA2134 x1/2; R₁ = 7.5 kΩ; R₂ = 5.6 kΩ; R₃ = 360 Ω; C₁ = 3300 pF; C₂ = 680 pF; Gain = 0.747;
f_{–3 dB} = 53 kHz.

Figure 37. AC-Coupled, Post-LPF and Differential to Single-Ended Buffer

NOTE: Amplifier is an NE5532A x 1/2 or OPA2134 x1/2; R₁ = 15 kΩ; R₂ = 11 kΩ; R₃ = 820 Ω; C₁ = 1500 pF; C₂ = 330 pF; Gain = 0.733;
f_{–3 dB} = 54 kHz.

Figure 38. DC-Coupled, Post-LPF and Differential to Single-Ended Buffer

8.2.1 Design Requirements

• Control: Hardware, I²C, or SPI
• Audio Input: PCM Serial Data, TDM, or DSP
• Audio Output: (1.6 × VCC1) Vpp Analog Audio Biased to (0.5 × VCC1) V
• Master Clock: PLL170X IC

8.2.2 Detailed Design Procedure