3 nV/√Hz, Low Power
Instrumentation Amplifier
Enhanced Product
AD8421-EP
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FEATURES
Specified from −55°C to 125°C
0.9 μV/°C maximum input offset voltage drift
5 ppm/°C maximum gain drift (G = 1)
Low power
2.3 mA maximum supply current
Low noise
3.2 nV/√Hz maximum input voltage noise at 1 kHz
200 fA/√Hz current noise at 1 kHz
Excellent ac specifications
2 MHz bandwidth (G = 100)
0.6 μs settling time to 0.001% (G = 10)
80 dB minimum CMRR at 20 kHz (G = 1)
High precision dc performance
84 dB CMRR minimum (G = 1)
2 nA maximum input bias current
Inputs protected to 40 V from opposite supply
Gain set with a single resistor (G = 1 to 10,000)
ENHANCED PRODUCT FEATURES
Supports defense and aerospace applications (AQEC standard)
Military temperature range (−55°C to +125°C)
Controlled manufacturing baseline
One assembly/test site
One fabrication site
Enhanced product change notification
Qualification data available on request
PIN CONNECTION DIAGRAM
TOP VIEW
(Not to Scale)
–IN
1
R
G
2
R
G
3
+IN
4
+V
S
8
V
OUT
7
REF
6
–V
S
5
AD8421-EP
11139-001
Figure 1.
10µ
1n
100 1M
TOTAL NOISE DENSITY AT 1kHz (V/√Hz)
SOURCE RESISTANCE, R
S
(Ω)
1µ
100n
10n
1k 10k 100k
G = 100
AD8421
BEST AVAILABLE
1mA LOW POWER IN-AMP
BEST AVAILABLE
7mA LOW NOISE IN-AMP
R
S
NOISE ONLY
11139-078
Figure 2. Noise Density vs. Source Resistance
GENERAL DESCRIPTION
The AD8421-EP is a low cost, low power, extremely low noise,
ultralow bias current, high speed instrumentation amplifier that
is ideally suited for a broad spectrum of signal conditioning and
data acquisition applications. This product features extremely
high CMRR, allowing it to extract low level signals in the presence
of high frequency common-mode noise over a wide
temperature range.
The 10 MHz bandwidth, 35 V/μs slew rate, and 0.6 μs settling
time to 0.001% (G = 10) allow the AD8421-EP to amplify high
speed signals and excel in applications that require high channel
count, multiplexed systems. Even at higher gains, the current
feedback architecture maintains high performance; for example,
at G = 100, the bandwidth is 2 MHz and the settling time is
0.8 μs. The AD8421-EP has excellent distortion performance,
making it suitable for use in demanding applications such as
vibration analysis.
The AD8421-EP delivers 3 nV/√Hz input voltage noise and
200 fA/√Hz current noise with only 2 mA quiescent current,
making it an ideal choice for measuring low level signals. For
applications with high source impedance, the AD8421-EP employs
innovative process technology and design techniques to provide
noise performance that is limited only by the sensor.
The AD8421-EP uses unique protection methods to ensure robust
inputs while still maintaining very low noise. This protection
allows input voltages up to 40 V from the opposite supply rail
without damage to the part.
A single resistor sets the gain from 1 to 10,000. The reference
pin can be used to apply a precise offset to the output voltage.
The AD8421-EP is specified over the military temperature range of
−55°C to +125°C. It is available in an 8-lead MSOP package.
Additional application and technical information can be found
in the AD8421 data sheet.
