Datasheet

POWER SUPPLY AND GROUNDING
DAC OUTPUT FILTER CIRCUITS
–
2
3
1
OPA2134
+
V
OUT
R
4
C
2
C
1
R
3
R
2
R
1
V
IN
A
V
+ *
R
2
R
1
S0053-01
PCB LAYOUT GUIDELINES
PCM1680
SLES133B – MARCH 2005 – REVISED OCTOBER 2008 .................................................................................................................................................. www.ti.com
The PCM1680 requires 5 V for the analog supply and digital supply. The 5-V supply is used to power not only
the DAC analog and output filter circuitry, but also the digital filter and serial interface circuitry. For best
performance, a 5-V supply using a linear regulator is recommended.
Four capacitors are required for supply bypassing, as shown in Figure 32 . These capacitors should be located as
close as possible to the PCM1680 package. The 10- µ F capacitor should be tantalum or aluminum electrolytic,
while the three 1- µ F capacitors are ceramic.
Δ Σ 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 is accomplished by a
combination of on-chip and external low-pass filtering.
Figure 31 and Figure 33 show the recommended external low-pass active filter circuits for dual- and
single-supply applications. These circuits are second-order Butterworth filters using a multiple-feedback (MFB)
circuit arrangement, which reduces sensitivity to passive component variations over frequency and temperature.
For more information regarding MFB active filter design, see Dynamic Performance Testing of Digital Audio D/A
Converters (SBAA055 ).
Because the overall system performance is defined by the quality of the DACs and their associated analog
output circuitry, high-quality audio operational amplifiers are recommended for the active filters. Texas
Instruments ’ OPA2134 and OPA2353 dual operational amplifiers are shown in Figure 31 and Figure 33 , and are
recommended for use with the PCM1680.
Figure 33. Dual-Supply Filter Circuit
A typical PCB floor plan for the PCM1680 is shown in Figure 34 . A ground plane is recommended, with the
analog and digital sections being isolated from one another using a split or cut in the circuit board. The PCM1680
should be oriented with the digital I/O pins facing the ground plane split/cut to allow for short, direct connections
to the digital audio interface and control signals originating from the digital section of the board.
Separate power supplies are recommended for the digital and analog sections of the board. This separation
prevents the switching noise present on the digital supply from contaminating the analog power supply and
degrading the dynamic performance of the PCM1680. 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 35
shows the recommended approach for single-supply applications.
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Product Folder Link(s): PCM1680