Analog Inputs; Iepe Interface - Analog Devices EVAL-ADAQ7767-1 User Manual

User Guide
EVALUATION BOARD HARDWARE

ANALOG INPUTS

The analog inputs, AINP and AINN, are accessible either through
the Subminiature Version B (SMB) connectors, or the turrets (T1
and T2). A Subminiature Version A (SMA) connector is also provid-
ed to connect to the IEPE sensor, which receives its current bias
from the on-board IEPE interface.
The default settings of the EV-ADAQ7767-1FMC1Z are as follows:
Analog inputs to ADAQ7767-1
►
and IEPE_IN is disconnected by P4.
The AINP and AINN inputs are buffered by a pair of optional
►
amplifiers, ADA4625-1 (U2 and U3).
Using the ADR444 (U4) as a 4.096 V reference and the IN2+
►
and IN2− inputs of the ADAQ7767-1, the full-scale differential
input range is ±11.2 V.
See Table 2 for the suggested power supply rails and
the necessary jumper positions and link options for the different in-
put configurations and input ranges. It is recommended to use a low
distortion AC source, such as the Audio Precision APx555 series,
when evaluating the dynamic performance of the ADAQ7767-1.

IEPE INTERFACE

An IEPE sensor can be used as an input to the EV-
ADAQ7767-1FMC1Z through the SMA connector at IEPE_IN. The
on-board IEPE interface biases the IEPE sensor, which operates
Table 1. Jumper Settings when Applying an IEPE Sensor Input
Function
IEPE Input
Single-Ended Input
Input Buffer U2
Input Buffer U3
Input Range
IEPE Input Coupling
IEPE Interface Supply (HV_VDD)
S2
analog.com
obtained from AINP and AINN,
Table 3 for
Recommended
Link Jumper Position for IEPE Input
P4 Insert jumper
P3 Insert jumper
JP1 Position A
JP2 Position A
JP3 Position B
JP4 Position B
P1, P2 Connect Pin 1 and Pin 2 (IN3+ and IN3−)
R13 0 Ω at R13
JP5 Position A
SW_S1 High
Low
SW_S2 High
Low
EVAL-ADAQ7767-1
by providing a 24 V rail at HV_VDD via the on-board supply or
an external supply, and switches on SW_S1 and SW_S2 on the
S2 mechanical switch. Inserting P4 connects the IEPE input to the
ADAQ7767-1. With a dropout of 1.2 V across the current source
(LT3092, U6) delivering a 4.5 mA bias to the IEPE sensor, this
circuit complies to the usable excitation voltage and current bias of
a typical IEPE interface (see Figure
from the IEPE sensor, the ADG5421F
is placed at the IEPE input. Under normal operating conditions, the
IEPE LED indicator (DS1) is on.
Most IEPE sensors have their output biased at 8 V to 14 V, with
an AC swing ±5 V around the bias. The EV-ADAQ7767-1FMC1Z
can be modified to allow an AC-coupled or DC-coupled IEPE input.
By default, the 0 Ω resistor at R13 configures the IEPE input to
be DC-coupled. The ADAQ7767-1 28 V (IN3) input is designed to
allow direct DC-coupled connections to IEPE sensors. For an AC-
coupled IEPE input, simply replace R13 with a ceramic capacitor,
and insert a resistor at R14 to implement a high-pass filter with
a cut-off frequency at the subhertz range. The AC-coupled IEPE
signal swing is suitable for the 4.096 V (IN1) or the 11.2 V (IN2)
input ranges of the ADAQ7767-1, depending on the AC swing of
the IEPE sensor.
Table 1 summarizes the recommended jumper settings related to
using an IEPE sensor input.
Comment
Connects IEPE_IN to ADAQ7767-1.
Shorts AINN to GND to allow single-ended input.
U2 acts as a high-impedance buffer to IEPE_IN.
Bypasses U3 to allow direct INx− short to GND.
Recommends use of IN3 (28 V) input range, which is designed
for a DC-coupled IEPE sensor input.
IEPE input is DC-coupled (default). Optionally, replace R13 with
a capacitor to have an AC-coupled IEPE input.
IEPE interface uses on-board supply INT_VDD (default).
Optionally, change to Position B to use an external supply,
EXT_VDD.
ADG5421F Channel 1 Enable. Connects IEPE interface to
IEPE_IN.
Disconnects IEPE interface from IEPE_IN.
ADG5421F Channel 2 Enable. Connects IEPE_IN to
ADAQ7767-1.
Disconnects IEPE_IN from ADAQ7767-1.
7). For overvoltage protection
(U5) fault protection switch
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