OPA1632 Datasheet, PDF (6/12 Pages) Texas Instruments – High-Perfomance, Fully-Differential AUDIO OP AMP

OPA1632
SBOS286 − DECEMBER 2003
APPLICATIONS INFORMATION
Figure 1 shows the OPA1632 used as a differential-output
driver for the PCM1804 high-performance audio ADC.
Supply voltages of ±15V are commonly used for the
OPA1632. The relatively low input voltage swing required
by the ADC allows use of lower power-supply voltage, if
desired. Power supplies as low as ±8V can be used in this
application with excellent performance. This reduces
power dissipation and heat rise. Power supplies should be
bypassed with 10µF tantalum capacitors in parallel with
0.1µF ceramic capacitors to avoid possible oscillations
and instability.
The V_COM reference voltage output on the PCM1804 ADC
provides the proper input common-mode reference
voltage (2.5V). This V_COM voltage is buffered with op amp
A₂ and drives the output common-mode voltage pin of the
OPA1632. This biases the average output voltage of the
OPA1632 to 2.5V.
The signal gain of the circuit is generally set to
approximately 0.25 to be compatible with commonly-used
audio line levels. Gain can be adjusted, if necessary, by
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changing the values of R₁ and R₂. The feedback resistor
values (R₃ and R₄) should be kept relatively low, as
indicated, for best noise performance.
R₅, R₆, and C₃ provide an input filter and charge glitch
reservoir for the ADC. The values shown are generally
satisfactory. Some adjustment of the values may help
optimize performance with different ADCs.
It is important to maintain accurate resistor matching on
R₁/R₂ and R₃/R₄ to achieve good differential signal
balance. Use 1% resistors for highest performance. When
connected for single-ended inputs (inverting input
grounded, as shown in Figure 1), the source impedance
must be low. Differential input sources must have
well-balanced or low source impedance.
Capacitors C₁, C₂, and C₃ should be chosen carefully for
good distortion performance. Polystyrene, polypropylene,
NPO ceramic, and mica types are generally excellent.
Polyester and high-K ceramic types such as Z5U can
create distortion.
Balanced or +
Single−Ended
Input ^−
V+
+8V to +16V
10µF
+
0.1µF
R₃
270Ω
C₁
1nF
R₁
1kΩ
8
3
5
R₂
V_OCM
2 _OPA1632
1kΩ
1
64
7
C₂
1nF
R₅
40Ω
R₆
40Ω
R₄
270Ω
C₃
2.7nF
1/2
PCM1804
V_COM
(2.5V)
Enable⁽¹⁾
NOTE: (1) Leave open to enable.
Logic signals referenced to V− supply.
See the Shutdown Function section.
0.1µF
10µF
OPA134
1kΩ
0.1µF
−8V to −16V
V−
Figure 1. ADC Driver for Professional Audio
6