OP292_02 Datasheet, PDF (10/20 Pages) Analog Devices – Dual/Quad Single-Supply Operational Amplifiers

OP292/OP492
CH A: 800dV FS
100dV/DIV
MKR: 16.9␮V/ͱHz
0Hz
MKR: 1000 Hz
25 kHz
BW: 150 Hz
TPC 31. Voltage Noise Density
APPLICATION INFORMATION
Phase Reversal
The OP492 has built-in protection against phase reversal when
the input voltage goes to either supply rail. In fact, it is safe for
the input to exceed either supply rail by up to 0.6 V with no risk
of phase reversal. However, the input should not go beyond the
positive supply rail by more than 0.9 V, otherwise the output
will reverse phase. If this condition can occur, the problem can
be fixed by adding a 5 k⍀ current limiting resistor in series with
the input pin. With this addition, the input can go to more than
5 V beyond the positive rail without phase reversal.
An input voltage that is as much as 5 V below the negative rail
will not result in phase reversal.
OV
11.8V p-p
5V
؉
OP492
؊
1V
100
90
2K⍀
10
0%
5µS
Figure 1. Output Phase Reverse If Input Exceeds the Posi-
tive Supply (V+) by More Than 0.9 V
OV
10V p-p
5V
؉
OP492
؊
1V
100
90
Power Supply Considerations
The OP292/OP492 are designed to operate equally well at single 5 V
or Ϯ15 V supplies. The lowest supply voltage recommended is 4.5 V.
It is a good design practice to bypass the supply pins with a 0.1 mF
ceramic capacitor. It helps improve filtering of high frequency noise.
For dual supply operation, the negative supply (V–) must be applied
at the same time, or before V؉. If V؉ is applied before V–, or in
the case of a loss of V– supply, while either input is connected to
ground or other low impedance source, excessive input current
may result. Potentially damaging levels of input current can de-
stroy the amplifier. If this condition can exist, simply add a l k⍀
or larger resistor in series with the input to eliminate the problem.
TYPICAL APPLICATIONS
Direct Access Arrangement for Telephone Line Interface
Figure 3 shows a 5 V- only transmit/receive telephone line inter-
face for a modem circuit. It allows full duplex transmission of modem
signals on a transformer-coupled 600 V line in a differential man-
ner. The transmit section gain can be set for the specific modem
device output. Similarly the receive amplifier gain can be appro-
priately selected based on the modem device input requirements.
The circuit operates on a single 5 V supply. The standard value
resistors allow the use of a SIP-packaged resistor array; coupled
with a quad op amp in a single package, this offers a compact,
low part-count solution.
To
Telephone
Line
1:1
T1
6.2V
300k⍀
300k⍀
6.2V
TX GAIN ADJUST
50k⍀
؉
1/4
OP492
؊
20k⍀
20k⍀
20k⍀ ^0.1␮F
5V dc
؉
1/4
OP492
؊
5k⍀
TRANSMIT
TXA
MODEM
100pF 5k⍀
10␮F
20k⍀
20k⍀
20k⍀
5V
0.1␮F
؊
1/4
OP492
؉
20k⍀
RX GAIN ADJUST
20k⍀ 50k⍀ 0.1␮F
؊
؉
RECEIVE
RXA
2k⍀ 10
0%
5µS
Figure 2. No Negative Rail Phase Reversal, Even with Input
Signal at 5 V Below Ground
Figure 3. A Universal Direct Access Arrangement for
Telephone Line Interface
A Single-Supply Instrumentation Amplifier
A low-cost, single-supply instrumentation amplifier can be built
as shown in Figure 4. The circuit utilizes two op amps to form a
high-input impedance differential amplifier. Gain can be set by
selecting resistor R_G which can be calculated using the transfer
function equation. Normally, V_REFERENCE is set to 0 V. Then the
output voltage is a function of the gain times the differential input
–10–
REV. B