SBAS052 Datasheet, PDF (12/17 Pages) Texas Instruments – Stereo Audio DIGITAL-TO-ANALOG CONVERTER MPEG2/AC-3 COMPATIBLE

Not Recommended For New Designs
POWER SUPPLY
CONNECTIONS
PCM1720 has two power supply connections: digital (V_DD)
and analog (V_CC). Each connection also has a separate
ground. If the power supplies turn on at different times, there
is a possibility of a latch-up condition. To avoid this condi-
tion, it is recommended to have a common connection
between the digital and analog power supplies. If separate
supplies are used without a common connection, the delta
between the two supplies during ramp-up time must be less
than 0.6V.
An application circuit to avoid a latch-up condition is shown
in Figure 10.
THEORY OF OPERATION
The delta-sigma section of PCM1720 is based on a 5-level
amplitude quantizer and a 3rd-order noise shaper. This
section converts the oversampled input data to 5-level delta-
sigma format. A block diagram of the 5-level delta-sigma
modulator is shown in Figure 11. This 5-level delta-sigma
modulator has the advantage of stability and clock jitter over
the typical one-bit (2-level) delta-sigma modulator.
The combined oversampling rate of the delta-sigma modu-
lator and the internal 8X interpolation filter is 48f_S for a
384f_S system clock, and 64f_S for a 256f_S system clock. The
theoretical quantization noise performance of the 5-level
delta-sigma modulator is shown in Figure 12.
Digital
Power Supply
Analog
Power Supply
V_DD
DGND
V_CC
AGND
3rd ORDER ∆Σ MODULATOR
20
0
–20
–40
–60
FIGURE 10. Latch-up Prevention Circuit.
–80
–100
–120
BYPASSING POWER SUPPLIES
–140
The power supplies should be bypassed as close as possible
to the unit. Refer to Figure 13 for optimal values of bypass
–160
0
5
10
15
20
25
capacitors. It is also recommended to include a 0.1µF ce-
Frequency (kHz)
ramic capacitor in parallel with the 10µF tantalum capacitor.
FIGURE 12. Quantization Noise Spectrum.
+
+
In
Z^–1
8f_S
–
18-Bit
+
+
Z^–1
–
+
+
Z^–1
Out
48f_S (384f_S)
64f_S (256f_S)
FIGURE 11. 5-Level ∆Σ Modulator Block Diagram.
®
PCM1720
+
+
+
5-level Quantizer
4
3
2
1
0
12