OP727 Analog Devices, OP727 Datasheet - Page 12

• Manufacturer Part Number: OP727
• Description: Precision Rail-to-Rail Output Single Supply Dual Op Amp
• Manufacturer: Analog Devices

Specifications of OP727

• -3db Bandwidth: 700kHz
• Slew Rate: 200mV/µs
• Vos: 30µV
• Ib: 5.5nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 15nV/rtHz
• Vcc-vee: 3V to 36V
• Isy Per Amplifier: 290µA
• Packages: SOIC,SOP

and limiting device power dissipation is of prime importance in
these designs. Figure 7 shows an example of 5 V, single-supply
current monitor that can be incorporated into the design of a voltage
regulator with foldback current limiting or a high current power
supply with crowbar protection. The design capitalizes on the
OP777’s common-mode range that extends to ground. Current
is monitored in the power supply return where a 0.1
resistor, R
inverting terminal becomes equal to the voltage at the noninverting
terminal through the feedback of Q1, which is a 2N2222 or equiva-
lent NPN transistor. This makes the voltage drop across R1 equal to
the voltage drop across R
becomes directly proportional to the current through R
the output voltage is given by:
The voltage drop across R2 increases with I
decreases with higher supply current being sensed. For the element
values shown, the V
The OP777/OP727/OP747 is very useful in many bridge applica-
tions. Figure 8 shows a single-supply bridge circuit in which its
output is linearly proportional to the fractional deviation ( ) of
the bridge. Note that = R/R.
In systems where dual supplies are available, the circuit of Figure
9 could be used to detect bridge outputs that are linearly related
to the fractional deviation of the bridge.
4
15V
REF
192
2
3
1/4 OP747
Figure 8. Linear Response Bridge, Single Supply
2.5V
R2
Figure 7. A Low-Side Load Current Monitor
SENSE
0.1 F
V
R1(1+ )
R1 = 100
OUT
, creates a very small voltage drop. The voltage at the
V
OUT
R1
OUT
Q1
5V
5
is 2.5 V for return current of 1 A.
R
R2 = 2.49k
4
SENSE
0.1
REF
SENSE
192
V
R1
2
R1(1+ )
3
. Therefore, the current through Q1
6
1M
R
R
V1
V2
2
1
5V
OP777
R
10.1k
15V
SENSE
RG = 10k
1/4 OP747
RETURN TO
GROUND
L
10.1k
increasing, so V
V
I
O
L
= 300
=
=
AR1 V
R1
R1
2R2
1M
15V
SENSE
shunt
REF
1/4 OP747
, and
OUT
+ 2.5V
V
O
–12–
A single-supply current source is shown in Figure 10 . Large resistors
are used to maintain micropower operation. Output current can be
adjusted by changing the R2B resistor. Compliance voltage is:
A single-supply instrumentation amplifier using one OP727
amplifier is shown in Figure 11. For true difference R3/R4 =
R1/R2. The formula for the CMRR of the circuit at dc is CMRR =
20 log (100/(1–(R2 R3)/(R1 R4)). It is common to specify t he
accuracy of the resistor network in terms of resistor-to-resistor
percentage mismatch. We can rewrite the CMRR equation to
reflect this CMRR = 20
high CMRR is a network of resistors that are well matched from
the perspective of both resistive ratio and relative drift. It should
be noted that the absolute value of the resistors and their absolute
drift are of no consequence. Matching is the key. CMRR is 100 dB
with 0.1% mismatched resistor network. To maximize CMRR,
one of the resistors such as R4 should be trimmed. Tighter match-
ing of two op amps in one package (OP727) offers a significant
boost in performance over the triple op amp configuration.
4
Figure 11. Single-Supply Micropower Instrumentation
Amplifier
15V
REF
192
3
R4 = 1M
V1
V2
Figure 10. Single-Supply Current Source
3.0
V
Figure 9. Linear Response Bridge
20k
V TO 30V
O
3.0
R3 = 10.1k
R2 = R2A + R2B
= 100 (V2
0.02mV
2mV
USE MATCHED RESISTORS
I
O
V TO 30V
=
= 1mA
R1
R1 = 100k
1/4 OP747
V
V
1/2 OP727
OUT
R2
100k
+15V
L
10pF
V1
15V
R2B
V1)
12k
11mA
log (10000/% Mismatch). The key to
1k
1/4 OP747
29V
V2
V
S
R1 = 10.1k
R(1+ )
V
SAT
290mV
R1
97.3k
R2A
OP777
2N2222
100k
10pF
R1
V
R
S
3.0
R2 = 1M
V
R2B
2.7k
V TO 30V
L
I
O
R
+
LOAD
1/2 OP727
+15V
R2
15V
1/4 OP747
V
O
=
=
V
R2
R1
O
R
REV.
R
V
REF
V
O
D