Datasheet

100mF
+
10-100nF
+
10-100nF
+
100mF
AGND
AGND
+
VREFR
REFGNDR
REFGNDL
VREFL
46
47
14
15
PCM4220
COMMON-MODE VOLTAGE OUTPUTS
VCOML
or
VCOMR
PCM4220
Precision,Low-NoiseOpAmp
(OPA227 orequivalent)
To
BiasNodes
R
(Optional)
DirectConnectto
High-ZBiasNode
(Z >10M )W
L
100nFto1mF
ClosetoICpins
PCM4220
www.ti.com ............................................................................................................................................. SBAS407C – DECEMBER 2006 – REVISED AUGUST 2009
Figure 36. Recommended Reference Capacitor Connections and Values
The PCM4220 includes two dc common-mode voltage outputs, VCOML (pin 13) and VCOMR (pin 48), which
correspond to the left and right input channels, respectively. The common-mode voltage is utilized to bias internal
op amps within the modulator section of the PCM4220, and may be used to bias external input circuitry when
proper design guidelines are followed. The common-mode voltages are derived from the VCC1 and VCC2
analog power supplies using internal voltage dividers. The voltage divider outputs are buffered and then routed to
internal circuitry and the VCOML and VCOMR outputs.
The common-mode output voltage is nominally equal to (0.4875 × VCC1) for VCOMR and (0.4875 × VCC2) for
VCOML. Given an analog supply voltage of +4.0V connected to both VCC1 and VCC2, the resulting
common-mode voltages are +1.95V.
The common-mode voltage outputs have limited drive capability. If multiple bias points are to be driven, or the
external bias nodes are not sufficiently high impedance, an external output buffer is recommended. Figure 37
shows a typical buffer configuration using the OPA227 . The op amp utilized in the buffer circuit should exhibit low
dc offset and drift characteristics, as well as low output noise.
Figure 37. Common-Mode Output Connections
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