DEMO MANUAL DC571A
LTC2418
8-/16-Channel Differential
DESCRIPTION
The LTC®2418 is a high resolution, 24-bit ΔΣ ADC with
5ppm INL and 5μV offset. Channel selection is programmed
through a simple serial interface. Since there is no latency,
each conversion is valid, even after a change in input
channel.
DC571A is a member of Linear Technology‘s QuikEval™
family of demonstration boards.
It is designed to allow easy evaluation of the LTC2418 and
may be connected directly to the target application’s analog
QUICK START PROCEDURE
Connect DC571 to DC590 USB serial controller using the
supplied 14-conductor ribbon cable. Connect DC590 to
host PC with a standard USB A/B cable. Run the evaluation software supplied with DC590 or downloaded from
www.linear.com/software. The correct program will be
loaded automatically.
24-Bit
signals while using the DC590 USB serial controller board
and supplied software to measure performance.
After evaluating with LTC’s software, the digital signals can
be connected to the application’s processor/controller for
development of the serial interface.
Design files for this circuit board are available at
www.linear.com/demo
http://
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
QuikEval is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners.
∆Σ ADC
Click the COLLECT button to start reading the input voltage.
Click the slider at the bottom of the strip-chart display to
change the input channel being displayed. For differential
measurements, Even channel pos and odd channel pos
correspond to even channels being positive inputs or
odd channels being positive inputs, respectively. See the
LTC2418 data sheet for details of channel selection.
Tools are available for logging data, changing reference
voltage, changing the number of points in the strip-chart
and histogram, and changing the number of points averaged for the DVM display.
Figure 1. DC590 Program
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DEMO MANUAL DC571A
HARDWARE SETUP
JUMPERS
JP1: Select the connection for the common pin, either
ground or external connection. Single-ended measurements are taken with respect to this pin.
JP2 and JP3: Select the source for differential reference.
Selecting 5V and GND will use the onboard 5V reference.
Select EXT to use an external reference.
JP5: Select notch frequency, 60Hz or 50Hz. Alternatively,
this jumper may be removed and an external conversion
clock applied to the center pin of JP5.
EXPERIMENTS
Figure 2 shows a number of applications for the LTC2418.
CH0, CH1, CH2
Channels 0 and 1 measure the differential output of an
Intersema MS5401 absolute pressure sensor. The 6.8k
resistor performs a first order temperature compensation
of the bridge output. CH2 measures the bridge voltage,
which provides a convenient temperature measurement.
This can also be used to perform further temperature
compensation in software.
CH3
Channel 3 measures the output of a thermistor in a half
bridge circuit. Many thermistors will work, the constraints
are that the bridge output must have an impedance of
less than 20k and the voltage must not go above V
CH4
Channel 4 measures the output of a type J thermocouple.
The circuit shown for channel 3 can be used for cold junction compensation. The cold junction sensor should be
close to the connections of the thermocouple to the board.
CH5
REF
/2.
CONNECTION TO DC590 SERIAL CONTROLLER
J1 is the power and digital interface connector. Connect
to DC590 serial controller with supplied 14-conductor
ribbon cable.
ANALOG CONNECTIONS
Analog signal connections are made via the turret posts
along the edge of the board (CH0 to CH15.) Also, if you are
connecting the board to an existing circuit, make full use
of the four ground connections at the corners of the board.
CH7
Channel 7 measures the output of a resistive attenuator.
CH8, CH9
Channels 8 and 9 measure the drop across a Deltec SWE3000-50 current shunt. Up to 3000A can be measured,
with a resolution of 60mA. With careful grounding, both
positive and negative currents can be measured. Care
must be taken to ensure that both inputs stay more positive than GND–0.3V.
CH10
Channel 10 is buffered with an LT1793 FET input amplifier
suitable for very high source impedance measurements.
CH11
Channel 11 measures the output of a precision rectifier.
CH12, CH13
Channels 12 and 13 measure a 3-wire RTD. The differential
voltage is the output, and CH12 single-ended reading is
the ground lead compensation.
Channel 5 measures the output of an Omega OS36-01
infrared thermocouple. This can be used for remote temperature measurement.
CH6
Channel 6 measures the photocurrent of a Hamamatsu
S1336-5BK photodiode.
2
CH14, CH15
Channels 14 and 15 measure the output of a 350Ω bridge.
This is standard for a wide variety of sensors. Typically
the full-scale output voltage is only 10mV. However, the
LTC2418 still gives 13 effective bits of resolution with no
amplification.
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