DEMO MANUAL DC573A
LTC2400
24-Bit Micropower No Latency
Delta Sigma ADC
DESCRIPTION
This demonstration board features the LTC
®
2400, a 24-bit
high performance ΔΣ analog-to-digital converter (ADC).
The LTC2400 combines exemplary DC accuracy (INL
±2ppm, 2.5μV offset, 0.3ppm noise) with an easy to use
SPI interface in a SO-8 package.
DC573 is a member of Linear Technology’s QuikEval™
family of demonstration boards. It is designed to allow
easy evaluation of the LTC2400 and may be connected
directly to the target application’s analog signals while
using the DC590 USB serial controller board and supplied
software to measure performance. The exposed ground
planes allow proper grounding to prototype circuitry. After
evaluating with LTC’s software, the digital signals can be
connected to the end application’s processor/controller
for development of the serial interface.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
BOARD PHOTO
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DEMO MANUAL DC573A
QUICK START PROCEDURE
Connect DC573 to a 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 evalu-
ation software supplied with DC590 or downloaded from
www.linear.com/software.
The correct program will be loaded
automatically. Click the COLLECT button to start reading
the input voltage. Details on software features are docu-
mented in the control panel’s help menu.
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 aver-
aged for the DVM display.
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DEMO MANUAL DC573A
HARDWARE SETUP
JUMPERS
JP1:
Select the reference source, either external or 5V
from the onboard LT1236 reference (default).
JP2:
Select the line rejection frequency, either 50Hz or
60Hz (default.) This jumper must be removed if applying
an external conversion clock to the F
O
turret post.
JP3:
Trigger mode, either normal (default) or externally
triggered.
JP4:
Trigger input signal. Pin 1 is a 5V logic signal, pin 2
is ground. When triggered mode is selected on JP3, a
rising edge starts a new conversion.
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 row of turret
posts along the edge of the board. Also, if you are connect-
ing the board to an existing circuit, the exposed ground
planes along the edges of the board may be used to form
a solid connection between grounds.
GND:
Ground turrets are connected directly to the PCB’s
ground planes.
V
CC
:
This is the supply for the ADC. Do not draw any
power from this point. External power may be applied to
this point after disabling the switching supply on DC590.
If the DC590 serial controller is being used, the voltage
must be regulated 5V only, as the isolation circuitry will
also be powered from this supply. Refer to the DC590
quick start guide for more details.
V
REF
:
This turret is connected to the LTC2400 reference
pin. If the onboard reference is being used, the reference
voltage may be monitored from this point. An external
ground referred reference may be connected to this terminal
if JP1 is configured for external reference.
V
IN
:
Input voltage to the LTC2400. The absolute range of
the input voltage is GND – 0.3V to V
CC
+ 0.3V. The range
for a valid conversion is GND – 0.125 • V
REF
to 1.125 V
REF
.
See Figure 1.
DC573a F01
Figure 1. LTC2400 Input Range
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DEMO MANUAL DC573A
EXPERIMENTS
OFFSET
Short V
IN
to ground. The offset is typically less than 0.5ppm
of V
REF
, with a maximum of 2ppm of V
REF
(2.5μV typical
and 10μV max when using a 5V reference.)
FULL SCALE
Short V
IN
to V
REF
. The full-scale error is typically less than
4ppm, with a maximum of 10ppm of V
REF
(20μV typical
and 50μV max when using a 5V reference.)
RMS NOISE
Short V
IN
to ground. The RMS noise display indicates
the RMS noise based on a number of samples that can
be set in the software options. With the input shorted to
ground, the indicated noise is the noise of the LTC2400
input. When another source is connected, the indicated
noise is the total noise of the LTC2400 and the source.
The USB controller powers the LTC2400 from an LT1761
low noise regulator. Although this device has exceptionally
low noise for a power regulator, it may still slightly elevate
the noise floor of the LTC2400. For lowest noise operation,
the LTC2400 may be powered from the onboard LT1236
reference by cutting the indicated trace and connecting
V
REF
to V
CC
as shown in Figure 3.
DC573a F02
Figure 2. Proper Measurement Equipment Setup
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DEMO MANUAL DC573A
EXPERIMENTS
DC573a F03
Figure 3. Low Noise Setup
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