PCM1730

SLES021 – NOVEMBER 2001

15

www.ti.com

PCB layout guidelines (continued)

Separate power supplies are recommended for the digital and analog sections of the board. This prevents the

switching noise present on the digital supply from contaminating the analog power supply and degrading the

dynamic performance of the D/A converters. In cases where a common 5-V supply must be used for the analog

and digital sections, an inductance (RF choke, ferrite bead) should be placed between the analog and digital

5-V supply connections to avoid coupling of the digital switching noise into the analog circuitry. Figure 10 shows

the recommended approach for single-supply applications.

bypass and decoupling capacitor requirements

Various-sized decoupling capacitors can be used, with no special tolerances being required. All capacitors

should be located as close to the appropriate pins of the PCM1730 as possible to reduce noise pickup from

surrounding circuitry. Aluminum electrolytic capacitors that are designed for hi-fi audio applications are

recommended for larger values, while metal-film or monolithic ceramic capacitors are used for smaller values.

I/V section

I/V conversion circuit by op amp IC and feedback resistor should achieve excellent performance of the

PCM1730. To obtain 0.0004% THD+N, 117-dB signal-to-noise ratio audio performance, THD+N and input noise

performance by the op amp IC should be considered, especially if the input noise of the op amp directly gives

be connected as short distance.

post LPF design

Out-band noise level and attenuated sampling spectrum level are much lower than typical delta-sigma type DAC

due to the combination of a high-performance digital filter and advanced segment DAC architecture. Second-

order or third-order post LPF is recommended as post LPF of the PCM1730. Cutoff frequency of post LPF is

Digital

Logic

and

Audio

Processor

Digital Power

+VD

DGND

Digital Section

Analog Section

Return Path for Digital Signals

Analog Power

+VS

AGND

–VS

+5VA

Digital

Ground

Analog

Ground

Output

Circuits

PCM1730

AGND

VCC

VDD

DGND

REG

Figure 9. Recommended PCB Layout