ISL28533 Datasheet, PDF (25/30 Pages) Intersil Corporation – 5V, Rail-Rail I/O, Zero-Drift, Programmable Gain Instrumentation Amplifiers

ISL28533, ISL28534, ISL28535, ISL28633, ISL28634, ISL28635
Applications Information
Precision Sensor Amplifier
The ISL2853x and ISL2863x are a family of ultra high precision
instrumentation amplifiers. These amplifiers feature zero drift
circuitry that provides auto offset voltage correction and noise
reduction, delivering very low offset voltage drift of 5nV/°C and a
low 1/F noise frequency corner down in the sub Hz range. The
instrumentation amplifier integrates precision matched resistors
for the front gain stage and the differential second stage,
providing very high gain accuracy and excellent CMRR. The
precision performance makes these amplifiers ideal for analog
sensor front end, instrumentation and data acquisition
applications such as weigh scales, flow sensors and shunt
current sensing that require very low noise and high dynamic
range.
SINGLE-ENDED OUTPUT
The ISL28533, ISL28534 and ISL28535 family of parts are
differential input, single ended output instrumentation amplifiers
using a three op amp architecture (Figure 71). The first stage is
differential input/differential output and is used to set the gain.
The second stage is a difference amplifier which is used to
remove the common mode voltage from the differential signal.
With the integrated gain resistors and the programmable gains,
these instrumentation amplifiers require no external
components for gain setting and operation.
There is an additional uncommitted zero drift operational
amplifier included on the chip. This can be used to drive the REF
pin if needed to provide a low impedance to REF. The REF pin is
used to shift the output DC reference. Note that on this device the
REF input is a resistor that is part of the difference amplifier non-
inverting input. To ensure good common mode rejection in the
output stage the REF pin should be driven by a low impedance
source, such as the output of amplifier A4. Any parasitic
resistance added to the REF pin degrades the common mode
rejection of the difference amplifier.
INA-
VA-
VA+
INA+
G0
G1
+
A1
-
R_G
R_G
20kΩ 20kΩ
-
A3
+
OUTA
-
A2
+
20kΩ
3-STATE LOGIC FOR
R_G GAIN CONTROL
20kΩ
REF
OUT
IN-
-
A4
+
IN+
FIGURE 71. ISL2853x BLOCK DIAGRAM
DIFFERENTIAL OUTPUT
The ISL28633, ISL28634 and ISL28635 family of parts are
differential input, differential output instrumentation amplifiers
and are ideal as a pre-amplifier/driver for differential input ADCs
(Figure 72). With the integrated gain resistors and the
programmable gains, these instrumentation amplifiers require
no external components for gain setting and operation.
INA-
VA-
VA+
INA+
G0
G1
+
A1
-
R_G
20kΩ 20kΩ
-
A3
+
-
A2
+
-
+
R_G
A4
20kΩ
20kΩ
3-STATE LOGIC FOR
R_G GAIN CONTROL
OUTA+
1MΩ
REF
1MΩ
OUTA-
FIGURE 72. ISL2863x BLOCK DIAGRAM
The first stage amplifier is identical to the first stage in the
ISL2853x family. The output stage is a difference amplifier which
is configured to provide differential output drive. The REF pin is
also available on this device and can be used to provide a DC
shift of the output signal. On this device the REF pin is a high
impedance input of an operational amplifier. The voltage used to
drive this pin can be developed using a resistor divider without
the need of an additional buffer without penalty of CMRR
degradation.
RFI FILTER
The instrumentation amplifier inputs of the ISL2853x and
ISL2863x have RFI filters for Electro Magnetic Interference (EMI)
reduction. In EMI sensitive applications, the high frequency RF
signal can appear as a rectified DC offset at the output of
precision amplifiers. Because the gain of the precision front end
can be 100 or greater it is critical not to amplify any conducted or
radiated noise that may be present at the amplifier inputs. The
RFI input is a 1kΩ, 3pF LPF with a corner frequency of
approximately 50MHz (See Figure 73).
INA-
RFI Filter
Fc = 50MHz
INA+
RFI Filter
Fc = 50MHz
+
A1
-
R_G
R_G
-
A2
+
FIGURE 73. RFI FILTER INPUTS
GAIN STAGE OUTPUT VA+/VA- PINS
The ISL2853x and ISL2863x instrumentation amplifiers include
pinouts for the output of the differential gain stage. VA+ is
referenced to the non-inverting input of the difference amplifier
while VA- is referenced to the inverting input. These pins can be
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FN8364.0
September 24, 2013