1
®
AN1290.2
ISL2827xINEVAL1Z Evaluation Board
User’s Guide
Introduction
The ISL2827xINEVAL1Z evaluation board is a design
platform containing all the circuitry needed to characterize
critical performance parameters of the ISL28270, ISL28271,
ISL28272 or ISL28273 Dual Instrumentation Amplifiers using
a variety of user defined test circuits.
The ISL2827x series of amplifiers are dual channel
instrumentation amplifiers optimized for 2.4V to 5V single
supplies. These devices feature an Input Range
Enhancement Circuit (IREC) which enables the inputs to
swing to the rails. The ISL28270 and ISL28273 maintain
CMRR performance from the positive rail down to within
50mV of the negative rail. The ISL28271 and ISL28272 can
swing 100mV beyond the rails. The output operation of all
devices is rail-to-rail. The ISL28270 and ISL28272 are
compensated for a minimum gain of 100 and the ISL28271
and ISL28273 are compensated for a minimum gain of 10.
Reference Documents
• ISL28270, ISL28273 Data Sheet, FN6260
• ISL28271, ISL28272 Data Sheet, FN6390
Evaluation Board Key Features
The ISL2827xINEVAL1Z is designed to be operated from a
single supply (+2.4VDC to +5VDC), or from split supplies
(±1.2VDC to ±2/5V). The board is configured for 2
independent instrumentation amplifiers connected for a
closed loop gain of 101 (ISL28270, ISL28272) or a gain of
10 (ISL28271, ISL28273) with inverting and non-inverting
high impedance terminated with 100k resistors to ground.
Each amplifier contains it’s own VREF input to establish an
input common mode reference. An ENABLE select switch is
provided for each amplifier to be used to save power by
powering the device down.
Power Supplies (Refer to Figure 1)
External power connections are made through the VSP (+V),
VSM (-V) and GND connections on the evaluation board.
For single supply operation, the VSM (-V) and GND pins are
tied together to the power supply negative terminal. For split
supplies, VSP (+V) and VSM (-V) terminals connect to their
respective power supply terminals. Resistors R
32
and R
33
are 0
Ω
but can be changed by the user to provide power
supply filtering, or
to
reduce the voltage rate-of-rise to less
than
±1
V/µs. Anti-reverse diodes D
1
and D
2
protect the
circuit in the case of accidental polarity reversal.
Amplifier Configuration (Refer to Figure 2)
The schematic of each of the two op amps with the
components supplied is shown in Figure 2. The circuit
implements a differential input instrumentation amp with a
closed loop gain of 101 for the ISL28270 and ISL28272, and
10 for the ISL28271, ISL28273. The circuit can operate from
a single 2.4VDC to +5VDC supply, or from dual supplies
from ±1.2VDC to ±2.5VDC.The output common mode
reference is applied to the VREF pin, and has a range from
ground (VM) to VP.
C
3
C
4
D
2
R
33
VSM
0.1µF
VM
1
2
10µF
1
2
D
1
1
1
1
2
2
D
3
1
2
VP
0.1µF
1
2
1
1
C
5
R
32
0
0
GND
VSP
3
A
NC
C
FIGURE 1. POWER SUPPLY CIRCUIT
-
+
-
+
IN+
IN-
FB+
FB-
R
F
R
G
VREF(x)
IN+(x)
IN-(x)
GND
100k
Ω
(ISL28270, ISL28272)
1k
Ω
100k
Ω
100k
Ω
VOUT(x)
1/2 ISL28270, ISL28271, ISL28272, ISL28273
VP
-V
ENABLE
10k
Ω
0
Ω
VM
VCM
IN+
IN-
VREF
9.09k
Ω
(ISL28271, ISL28273)
FIGURE 2. BASIC AMPLIFIER CONFIGURATION
Application Note
June 15, 2009
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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