AD8571ARMZ-R2 Analog Devices Inc, AD8571ARMZ-R2 Datasheet - Page 21

• Manufacturer Part Number: AD8571ARMZ-R2
• Description: IC OPAMP CHOPPER R-R 30MA 8MSOP
• Manufacturer: Analog Devices Inc

Specifications of AD8571ARMZ-R2

• Amplifier Type: Chopper (Zero-Drift)
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 0.4 V/µs
• Gain Bandwidth Product: 1.5MHz
• Current - Input Bias: 10pA
• Voltage - Input Offset: 1µV
• Current - Supply: 850µA
• Current - Output / Channel: 30mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -

THERMOCOUPLE
HIGH ACCURACY THERMOCOUPLE AMPLIFIER
Figure 66 shows a K-type thermocouple amplifier configuration
with cold-junction compensation. Even from a 5 V supply, the
AD8571 can provide enough accuracy to achieve a resolution of
better than 0.02°C from 0°C to 500°C. D1 is used as a tempera-
ture measuring device to correct the cold-junction error from
the thermocouple and should be placed as close as possible to
the two terminating junctions. With the thermocouple measuring
tip immersed in a 0°C ice bath, R6 should be adjusted until the
output is at 0 V.
Using the values shown in Figure 66, the output voltage tracks
temperature at 10 mV/°C. For a wider range of temperature
measurement, R9 can be decreased to 62 kΩ. This creates a
5 mV/°C change at the output, allowing measurements of up
to 1000°C.
PRECISION CURRENT METER
Because of its low input bias current and superb offset voltage at
single-supply voltages, the AD857x family is an excellent amplifier
for precision current monitoring. Its rail-to-rail input allows the
amplifier to be used as either a high-side or a low-side current
monitor. Using both amplifiers in the AD8572 provides a simple
method to monitor both current supply and return paths for
load or fault detection.
Figure 67 shows a high-side current monitor configuration.
Here, the input common-mode voltage of the amplifier is at or
near the positive supply voltage. The rail-to-rail input of the
amplifier provides a precise measurement, even with the input
common-mode voltage at the supply voltage. The CMOS input
structure does not draw any input bias current, ensuring a
minimum of measurement error.
The 0.1 Ω resistor creates a voltage drop to the noninverting
input of the AD857x. The output of the amplifier is corrected
until this voltage appears at the inverting input, which creates a
current through R1 that in turn flows through R2. The monitor
output is given by
40.7µV/°C
K-TYPE
12V
0.1µF
Figure 66. Precision K-Type Thermocouple Amplifier
–
+
with Cold-Junction Compensation
2
REF02EZ
–
+
1N4148
D1
5.62kΩ
4
10.7kΩ
2.74kΩ
R4
6
R1
R2
5V
R3
53.6Ω
200Ω
R6
R5
40.2kΩ
453Ω
R8
2
3
124kΩ
5V
R9
4
7
0.1µF
10µF
0V TO 5V
(0°C TO 500°C)
AD8571
6
Rev. E | Page 21 of 24
Using the components shown in Figure 67, the monitor output
transfer function is 2.49 V/A.
Figure 68 shows the low-side monitor equivalent. In this circuit,
the input common-mode voltage to the AD8572 is at or near
ground. Again, a 0.1 Ω resistor provides a voltage drop propor-
tional to the return current. The output voltage is given as
For the component values shown in Figure 68, the monitor
output transfer function is V+ − 2.49 V/A.
PRECISION VOLTAGE COMPARATOR
The AD857x can be operated open loop and used as a precision
comparator. The AD857x have less than 50 μV of offset voltage
when they run in this configuration. The slight increase of
offset voltage stems from the fact that the autocorrection
architecture operates with the lowest offset in a closed-loop
configuration, that is, one with negative feedback. With 50 mV
of overdrive, the device has a propagation delay of 15 μs on the
rising edge and 8 μs on the falling edge.
Care should be taken to ensure that the maximum differential
voltage of the device is not exceeded. For more information, see
the Input Overvoltage Protection section.
Monitor Output = R2 × (R
Monitor
MONITOR
MONITOR
OUTPUT
OUTPUT
V+
Output
Figure 67. High-Side Load Current Monitor
Figure 68. Low-Side Load Current Monitor
Si9433
100Ω
100Ω
R1
M1
R1
Q1
V+
D
S
R2
2.49kΩ
=
R2
2.49kΩ
R
R
V
SENSE
0.1Ω
0.1Ω
SENSE
AD8571/AD8572/AD8574
+
G
−
⎛
⎜
⎝
R
R
2
SENSE
3
2
1
2
3
+
AD8572
–
I
×
L
/R1) × I
1/2
R
V+
V+
SENSE
4
I
8
L
1/2 AD8572
0.1µF
×
L
1
I
L
⎞
⎟
⎠
V+
LOAD
LOAD
(23)
(24)