OP492GS(RevB) 데이터 시트보기 (PDF) - Analog Devices
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OP492GS Datasheet PDF : 20 Pages
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OP292/OP492
voltage. However, the output can be offset by setting VREFERENCE
from 0 V to 4 V, as long as the input common-mode voltage of
the amplifier is not exceeded.
؉
VIN
؊
1/2 1
OP292
5V
58
1/2 7
OP292
4
VOUT
VREF
20k⍀
5k⍀
5k⍀
20k⍀
VOUT = 5 ؉40k⍀ + VREF
RG
RG
Figure 4. A Single-Supply Instrumentation Amplifier
In this configuration, while the output can swing to near zero
volts, one needs to be careful because the input’s common-mode
voltage range cannot operate to zero volts. This is because of the
limitation of the circuit configuration where the first amplifier
must be able to swing below ground in order to attain a 0 V
common-mode voltage, which it cannot do. Depending on the
gain of the instrumentation amplifier, the input common-mode
extends to within about 0.3 V of zero. One can easily calculate
the worst-case common-mode limit for a given gain.
DAC Output Amplifier
The OP292/OP492 are ideal for buffering the output of single-
supply D/A converters. Figure 5 shows a typical amplifier used to
buffer the output of a CMOS DAC that is connected for single-
supply operation. To do that, the normally current output 12-bit
CMOS DAC (R-2R ladder type) is connected backward to pro-
duce a voltage output. This operating configuration necessitates
a low voltage reference. In this case, a 1.235 V low-power reference
is used. The relatively high output impedance (10 k⍀) is buffered by
the OP292 and at the same time gained up to a much more usable
level. The potentiometer provides an accurate gain trim for a
4.095 V full-scale, allowing 1mV increment per LSB of control
resolution.
The DAC8043 device comes in an 8-pin DIP package providing
a cost-effective, compact solution to a 12-bit analog channel.
5V
7.5k⍀
5V
DAC8043
1 VREF
VDDDD 8
NC 2 VFB
CCLKlk 7
1.235V 3 t0
SRSIri 6
Ad589
4 VND
LD 5
5V
؉
1/2
OP292
؊
20k⍀
8.45k⍀
500k⍀
VOUT
1mV/LSB
0V؊4.095V
FS
A 50 Hz/60 Hz Single-Supply Notch Filter
Figure 6 shows a notch filter that achieves nearly 30 dB of 60 Hz
rejection while powered by only a single 12 V supply. The circuit
also works well on 5 V systems. The filter utilizes a twin-T configu-
ration whose frequency selectivity depends heavily on the relative
matching of the capacitors and resistors in the twin-T section.
Mylar is a good choice for the twin-T’s capacitors, and the relative
matching of the capacitors and resistors determines the filter’s
passband symmetry. Using 1% resistors and 5% capacitors
produces satisfactory results.
The amount of rejection and the Q of the filter is solely determined
by one resistor, and is shown in the table. The bottom amplifier
is used to split the supply to bias the amplifier to midlevel. The
circuit can be modified to reject 50 Hz by simply changing the
resistors in the twin-T section (Rl through R4) from 2.67 k⍀ to
3.16 k⍀, and changing R5 to 1⁄2 of 3.16 k⍀. For best results,
the common value resistors can be from a resistor array for opti-
mum matching characteristics.
R2
2.67k⍀
R1
2.67k⍀
C1
C2
12V
؉1/4
1F
1F
OP492
VIN
؊
؉1/4
OP492
؊
R3
R4
2.67k⍀
2.67k⍀
R6
100k⍀
C3
2F
(1F؋2)
R5
1.335k⍀
(2.67k،2)
R7 RQ
1k⍀ 8k⍀
VOUT
12V
R8
100k⍀
R9
100k⍀
؉
C4
1F
؉1/4
OP492
؊
6V
NOTE
FOR 50Hz APPLICATION
CHANGE R12؊R4 TO 3.16k⍀
AND R5 TO 1.58k (3.16k⍀ 2)
FILTER Q RQ (k⍀) REJECTION (dB) VOLTAGE GAIN
0.75
1.0
40
1.33
1.00
2.0
35
1.50
1.25
3.0
30
1.60
2.50
8.0
25
1.80
5.00
18
20
1.90
10.00
38
15
1.95
Figure 6. A Single-Supply 50 Hz/60 Hz Notch Filter
5V
5V
6
5k⍀
2
8
0.01F 1/2
1
0.022F
5
1/2
OP292
7
VIN
3 OP292
4
1.1k⍀ 14.3k⍀
100F 1.78k⍀ 16.2k⍀
2200pF
5k⍀
3300pF
VOUT
LD SRI CLK
DIGITAL
CONTROL
Figure 5. A 12-Bit Single-Supply DAC with Serial Bus Control
Figure 7. A 4-Pole Bessel Low-Pass Filter Using Sallen-Key
Topology
A 4-Pole Bessel Low-Pass Filter
The linear phase filter in Figure 7 is designed to roll off at a
voiceband cutoff frequency of 3.6 kHz. The 4 poles are formed
by two cascading stages of two-pole Sallen-Key filters.
REV. B
–11–
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