1
Application Note 1748
ISL28617SMXXEV1Z User’s Guide
Introduction
The ISL28617SMXXEV1Z evaluation board is designed to assess
the performance of the ISL28617 differential input, differential
output, precision instrumentation amplifier (in-amp). With an
input voltage range up to ±34V, a supply voltage range of 8V (±4V)
to 40V (±20V) and gain ranging from 0.1 to 10,000, this in-amp is
ideal for a wide variety of applications. The gain accuracy is
limited only by the matching of the gain resistors, and the output
is capable of driving rail-to-rail.
The board is configured for ease of use, but allows for more
complex variations to fit the user’s need, as discussed in the
following sections. The evaluation board includes test points
(V
CC
, V
EE
, and GND) for the power supply inputs, and is
configured for operation from split supplies between ±4V to
±20V. There are two pairs of test points for the differential input
and output as well (V
IN+
, V
IN-
, V
OUT+
, and V
OUT-
). The board is
available in three different gain configurations: 0.25, 10 and
100. Ordering information is shown in Table 3.
Reference Documents
• ISL28617 Data sheet, FN6562
Power Supplies
External power connections are made to the positive supply rail
(TP1), the negative supply rail (TP9), and ground (TP4) for split
supply operation. The operating voltage range is ±4V to ±20V.
The in-amp has two distinct sets of power supplies; one on the
input stage and one on the output stage. For the evaluation
board, the output stage supplies are tied to the input stage
supplies, and the common mode voltage is tied to ground. The
supply voltage on the input stage must be 3V above and below
the maximum and minimum input signal voltage, respectively.
Note that while the output stage is rail-to-rail, the feedback
returns to the input stage, which is not rail-to-rail. Therefore, the
input power supply must be 3V above and below the maximum
and minimum output signal as well. Table 2 provides suggested
supply voltages for the three standard boards. For more
information, reference “Setting the Power Supply Voltages” on
page 13 of the ISL28617 data sheet.
If the user wants to control the output supplies separately, the R3
and R5 resistors must be removed, and the V
CO
(TP2) and V
EO
(TP6) test points are used for the positive output supply and
negative output supply respectively (reference evaluation board
schematic in Figure 4). Single supply operation requires removing
R7 and attaching the desired common mode voltage to the V
REF
(TP10) test point. Using the separate supply feature enables input
signals riding on a high common mode voltage to be level shifted
to a low voltage device such as an analog to digital converter
(ADC). The rail-to-rail output stage can be powered from the same
supplies as the ADC while preserving the in-amp’s maximum input
dynamic range. Once again, the positive input power supply must
be 3V above the maximum output signal, and the negative input
power supply must be 3V below the minimum output signal.
Amplifier Configuration
The ISL28617 evaluation board schematic is shown in Figure 4
with a closed loop gain of 10 and split supply operation with
input and output supplies tied together. Other gain options are
0.25 and 100, with the required resistor and capacitor changes
listed in Table 1. The in-amp gain is controlled through R1 and
R2, the feedback and input resistors, with the following simple
formula:
R1 and R2 also limit the maximum signal size at the input and
output due to the amplifier architecture. Table 2 shows the signal
limits for the boards at the preset resistor values. For more
information, refer to “Setting the Feedback Gain R
FB
“ and
“Setting the Input Gain R
IN
” on page 13 of the ISL28617 data
sheet.
The evaluation board allows the user to add an optional low pass
RC filter to the signal path. R8, R9, and C6 create a filter on the
output of the in-amp, while R10, R11, and C7 create a filter on
the input. The gain of 0.25 board option includes a filter on the
input to avoid gain peaking at the limits of the gain bandwidth
product.
TABLE 1. COMPONENTS PARTS LIST
DEVICE # VALUE DESCRIPTION
C1-C5 0.01µF Decoupling Capacitors
C6 Open Optional Output Filter Capacitor
C7 Open Optional Input Filter Capacitor
1.2pF Input Filter Capacitor (G = 0.25)
D1, D2 S1A Reverse Power Protection
R1 30.1kΩ Feedback Gain Resistor (G = 0.25)
100kΩ Feedback Gain Resistor (G = 10, 100)
R2 121kΩ Input Gain Resistor (G = 0.25)
10kΩ Input Gain Resistor (G = 10)
1kΩ Input Gain Resistor (G = 100)
R3, R5, R7 0Ω User Selectable Resistors
R8, R9 0Ω Optional Output Filter Resistors
R10, R11 0Ω Optional Input Filter Resistors
49.9kΩ Input Filter Resistors (G = 0.25)
R4, R6 1MΩ Ground Input for Stability
U1 ISL28617 TSSOP 24-Pin Package
A
V
R1
R2
-------
=
(EQ. 1)
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Copyright Intersil Americas Inc. 2012. All Rights Reserved.
1-888-INTERSIL or 1-888-468-3774
| Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
October 24, 2012
AN1748.2
