AD8638ARZ Analog Devices Inc, AD8638ARZ Datasheet - Page 15

• Manufacturer Part Number: AD8638ARZ
• Description: IC OPAMP CHOPPER R-R 37MA 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD8638ARZ

• Slew Rate: 2 V/µs
• Amplifier Type: Chopper (Zero-Drift)
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Gain Bandwidth Product: 1.5MHz
• Current - Input Bias: 1pA
• Voltage - Input Offset: 3µV
• Current - Supply: 1.25mA
• Current - Output / Channel: 37mA
• Voltage - Supply, Single/dual (±): 5 V ~ 16 V, ±2.5 V ~ 8 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Op Amp Type: Low Offset Voltage
• No. Of Amplifiers: 1
• Bandwidth: 1.5MHz
• Supply Voltage Range: 5V To 16V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

INFRARED SENSORS
Infrared (IR) sensors, particularly thermopiles, are increasingly
used in temperature measurement for applications as wide
ranging as automotive climate control, human ear thermometers,
home insulation analysis, and automotive repair diagnostics.
The relatively small output signal of the sensor demands high
gain with very low offset voltage and drift to avoid dc errors.
If interstage ac coupling is used, as shown in Figure 48, low
offset and drift prevent the output of the input amplifier from
drifting close to saturation. The low input bias currents generate
minimal errors from the output impedance of the sensor.
Similar to pressure sensors, the very low amplifier drift with
time and temperature eliminates additional errors once the
system is calibrated at room temperature. The low 1/f noise
improves SNR for dc measurements taken over periods often
exceeding one-fifth of a second.
Figure 48 shows a circuit that can amplify ac signals from
100 μV to 300 μV up to the 1 V to 3 V levels, with a gain of
10,000 for accurate analog-to-digital conversions.
–0.05
–0.05
–0.10
–0.15
0.15
0.10
0.05
0.05
0
0
Figure 47. Negative Input Overload Recovery for the AD8638
Figure 46. Positive Input Overload Recovery for the AD8638
V
A
SY
V
= –100
= ±8V
OUTPUT VOLTAGE
OUTPUT VOLTAGE
INPUT VOLTAGE
INPUT VOLTAGE
TIME (10µs/DIV)
TIME (10µs/DIV)
V
A
SY
V
= –100
= ±8V
0
–2.5
10
–5.0
–7.5
–10.0
5
0
–5
Rev. A | Page 15 of 20
PRECISION CURRENT SHUNT SENSOR
A precision current shunt sensor benefits from the unique
attributes of auto-zero amplifiers when used in a differencing
configuration, as shown in Figure 49. Current shunt sensors are
used in precision current sources for feedback control systems.
They are also used in a variety of other applications, including
battery fuel gauging, laser diode power measurement and
control, torque feedback controls in electric power steering, and
precision power metering.
In such applications, it is desirable to use a shunt with very low
resistance to minimize the series voltage drop; this minimizes
wasted power and allows the measurement of high currents
while saving power. A typical shunt might be 0.1 Ω. At measured
current values of 1 A, the output signal of the shunt is hundreds
of mV, or even V, and amplifier error sources are not critical.
However, at low measured current values in the 1 mA range,
the 100 μV output voltage of the shunt demands a very low offset
voltage and drift to maintain absolute accuracy. Low input bias
currents are also needed to prevent injected bias current from
becoming a significant percentage of the measured current. High
open-loop gain, CMRR, and PSRR help to maintain the overall
circuit accuracy. With the extremely high CMRR of the AD8638,
the CMRR is limited by the resistor ratio matching. As long as
the rate of change of the current is not too fast, an auto-zero
amplifier can be used with excellent results.
SUPPLY
e = 1,000 R
DETECTOR
100µV TO 300µV
Figure 48. AD8638 Used as a Preamplifier for Thermopile
100mV/mA
IR
S
100Ω
I
AD8638
Figure 49. Low-Side Current Sensing
100kΩ
100kΩ
100kΩ
16V
16V
C
C
AD8638
f
C
≈ 1.6Hz
10µF
100Ω
100Ω
10kΩ
VOLTAGE
10kΩ
TO BIAS
I
0.1Ω
R
S
100kΩ
16V
AD8638
AD8638
R
L