OP291GSZ-REEL7 Analog Devices Inc, OP291GSZ-REEL7 Datasheet - Page 21

• Manufacturer Part Number: OP291GSZ-REEL7
• Description: IC,Operational Amplifier,DUAL,BICMOS,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of OP291GSZ-REEL7

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.5 V/µs
• Gain Bandwidth Product: 3MHz
• Current - Input Bias: 30nA
• Voltage - Input Offset: 80µV
• Current - Supply: 260µA
• Current - Output / Channel: 16mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V, ±1.35 V ~ 6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A 3 V, COLD JUNCTION COMPENSATED
THERMOCOUPLE AMPLIFIER
The OP291 low supply operation makes it ideal for 3 V battery-
powered applications such as the thermocouple amplifier
shown in Figure 70. The K-type thermocouple terminates in an
isothermal block where the junction ambient temperature is
continuously monitored using a simple 1N914 diode. The diode
corrects the thermal EMF generated in the junctions by feeding
a small voltage, scaled by the 1.5 MΩ and 475 Ω resistors, to the
op amp.
To calibrate this circuit, immerse the thermocouple measuring
junction in a 0°C ice bath and adjust the 500 Ω potentiometer
to 0 V out. Next, immerse the thermocouple in a 250°C
temperature bath or oven and adjust the scale adjust
potentiometer for an output voltage of 2.50 V. Within this
temperature range, the K-type thermocouple is accurate to
within ±3°C without linearization.
SINGLE-SUPPLY, DIRECT ACCESS ARRANGEMENT
FOR MODEMS
An important building block in modems is the telephone line
interface. In the circuit shown in Figure 71, a direct access
arrangement is used to transmit and receive data from the
telephone line. Amplifier A1 is the receiving amplifier;
Amplifier A2 and Amplifier A3 are the transmitters. The fourth
amplifier, A4, generates a pseudo ground halfway between the
supply voltage and ground. This pseudo ground is needed for
the ac-coupled bipolar input signals.
ALUMEL
K-TYPE
THERMOCOUPLE
40.7μV/°C
CHROMEL
Figure 70. A 3 V, Cold Junction Compensated Thermocouple Amplifier
AL
CR
ISOTHERMAL
BLOCK
1N914
COLD
JUNCTIONS
AD589
11.2mV
7.15kΩ
1.5MΩ
1%
475Ω
1%
1%
1.235V
24.9kΩ
1%
2.1kΩ
1%
10kΩ
24.3kΩ
1%
500Ω
10 TURN
ZERO
ADJUST
4.99kΩ
1%
3.0V
2
3
OP291
1/2
4
8
1.33MΩ 20kΩ
SCALE
ADJUST
1
0V = 0°C
3V = 300°C
V
Rev. E | Page 21 of 24
OUT
The transmit signal, TXA, is inverted by A2 and then reinverted
by A3 to provide a differential drive to the transformer, where
each amplifier supplies half the drive signal. This is needed
because of the smaller swings associated with a single supply as
opposed to a dual supply. Amplifier A1 provides some gain for
the received signal, and it also removes the transmit signal
present at the transformer from the received signal. To do this,
the drive signal from A2 is also fed to the noninverting input of
A1 to cancel the transmit signal from the transformer.
The OP491 bandwidth of 3 MHz and rail-to-rail output swings
ensure that it can provide the largest possible drive to the
transformer at the frequency of transmission.
RXA
TXA
Figure 71. Single-Supply, Direct Access Arrangement for Modems
0.1μF
0.1μF
20kΩ,1%
0.0047μF
14
10
A4
1
9
6
5
750pF
OP491
OP491
A1
37.4kΩ
390pF
1/4
1/4
37.4kΩ,1%
OP491
20kΩ,1%
OP491
20kΩ,1%
3.3kΩ
11
1/4
1/4
4
A3
OP191/OP291/OP491
A2
7
8
12
13
2
3
100kΩ
3V OR 5V
100kΩ
20kΩ,1%
5.1V TO 6.2V
ZENER 5
20kΩ,1%
475Ω,1%
10μF
0.033μF
0.1μF
T1
1:1