QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010
2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C
1
LTC2493, LTC2489, LTC2487
DESCRIPTION
Demonstration circuit 1010A-A features the LTC2493
2/4 Channel, 24-Bit ADC with I
2
C. Key DC specifica-
tions include 2ppm INL, 1ppm offset, 25ppm full-
scale error and 10nV/°C offset drift. In the
6.8Hz/600nV
RMS
mode, input normal mode rejection of
50Hz and 60Hz noise is better than 87dB. The
LTC2493 also includes an internal temperature sensor
that is accurate to 2 degrees C over the operating
temperature range.
The DC1010A-B features the LTC2489 16-Bit ADC
that is pin out and software compatible with the
LTC2493.
The DC1010A-C features the LTC2487 16-Bit ADC
that also includes a PGA with a gain range from 1 to
256 and the same temperature sensor as the
LTC2493.
The DC1010 is a member of Linear Technology‘s
QuickEval™ family of Demonstration Boards. It is de-
signed to allow easy evaluation of the LTC2493,
LTC2489 or LTC2487. DC1010 may be connected di-
rectly to the target application’s analog 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 / control-
ler for development of the serial interface.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
Figure 1. Proper Measurement Equipment Setup
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010
2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C
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QUICK START PROCEDURE
Connect the DC1010 to a DC590 USB Serial Con-
troller using the supplied 14 conductor ribbon ca-
ble. Connect DC590 to the host PC with a standard
USB A/B cable. Run the evaluation software sup-
plied with DC590 or downloaded from
www.linear.com. The correct program will be
loaded automatically. Click the COLLECT button to
start reading the input voltage. The software allows
for selecting the input channel, single ended or dif-
ferential mode and 50/60 Hz rejection settings. Se-
lecting 2x Speed located at the bottom of the strip-
chart display will double the data output rate at the
expense of offset accuracy (LTC2493 and LTC2487
only).
Tools are available for logging data, changing refer-
ence voltage, changing the number of points in the
strip chart and histogram, and changing the num-
ber of points averaged for the DVM display.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010
2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C
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HARDWARE SET-UP
JUMPERS
JP1, JP2 – Select the source for REF+ and REF-,
respectively. REF+ can be 5.00 volts from the on-
board LT1236 reference (default) or supplied exter-
nally. REF- can be Ground (0 volts, default) or sup-
plied externally.
JP3, JP4 – Control for I
2
C address lines A0 and A1
respectively. These lines can be floated by removing
the jumpers, grounded (Low) or tied to Vcc (High).
The default mode is JP3, JP4 tied to Vcc. This is
required for use with Quick Eval software. The ad-
dresses generated are shown below.
CA1 CA0 ADDRESS
LOW LOW 0010100
LOW HIGH 0010110
LOW FLOAT 0010101
HIGH LOW 0100110
HIGH HIGH 0110100 (Default)
HIGH FLOAT 0100111
FLOAT LOW 0010111
FLOAT HIGH 0100101
FLOAT FLOAT 0100100
CONNECTION TO DC590 SERIAL CONTROLLER
J2 is the power and digital interface connector.
Connect to a DC590 serial controller with the sup-
plied 14-conductor ribbon cable. Digital signals are
also connected to through-hole test points on the
circuit board.
ANALOG CONNECTIONS
Analog signal connections are made via the row of
turret posts along the edge of the board.
GND – Ground turrets are connected directly to the
internal analog ground plane.
VCC – 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 Vcc supply
on DC590. See the DC590 quick start guide for de-
tails.
REF+, REF- - These turrets are connected to the
LTC2487/2489/2493 REF+ and REF- pins. If the on-
board reference is being used, the reference voltage
may be monitored from this point. An external ref-
erence may be connected to these terminals if JP1
and JP2 are configured for external reference.
CH0 – CH3 – These are the differential inputs to the
LTC2493/2489/2487. They may be configured as
single–ended inputs with respect to the COM pin, or
as differential inputs (CH0-CH1, CH2-CH3) with the
polarity software selected.
DIGITAL CONNECTION
FO – Connects to the Frequency Control Pin. When
F
O
is connected to GND (Default connection), the
converter uses its internal oscillator running at
307.2 kHz. The conversion clock may also be over-
ridden by driving the F
O
pin with an external clock in
order to change the output rate and the digital filter
rejection null.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010
2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C
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EXPERIMENTS
INPUT NOISE
Solder a short wire between the CH0 and CH1 tur-
rets. Connect the inputs to ground through a short
wire and start taking data. LTC2493 Noise should
be approximately 0.12ppm of 5V (600nV RMS.) The
electrical noise of the LTC2489 is also 600nV RMS,
however this is masked by the 76.3µV quantization
level. If the input is well between code transitions,
the noise level will read zero. If the input is exactly
between two codes such that the two adjacent out-
put codes have equal probability, the noise level will
be approximately 7.9ppm. The input noise of the
LTC2487 is apparent at very high gain settings (128
or 256.) Note that with a 5V reference and gain set
to 256, 1LSB is equal to 298nV – which is lower
than the 600nVRMS electrical noise of the input
stage.
COMMON MODE REJECTION
Tie the two inputs (still connected together from
previous experiment) to ground through a short
wire and note the indicated voltage. Tie the inputs
to REF+; the difference should be less than 0.5 µV
due to the 140 dB+ CMRR of the LTC2493. The
LTC2489 will produce less than 1LSB difference.
INPUT NORMAL MODE REJECTION
The LTC2493 and LTC2487 SINC4 digital filter can
be software selected to reject 50Hz, 60Hz by 110dB,
or both 50 and 60Hz by 87dB. The LTC2489’s
SINC4 filter is fixed at 50/60Hz. To measure input
normal mode rejection, connect COM to a 2.5 volt
source such as an LT1790-2.5 reference or a power
supply. Connect any other input (CH0 – CH3) to the
same supply through a 10kΩ resistor. Apply a 10
Hz, 2V peak-to-peak sine wave to the input through
a 1uF capacitor.
Set the rejection frequency to 55Hz (LTC2493 only)
and start taking data. The input noise will be quite
large, and the graph of output vs. time should show
large variations.
Next, slowly increase the frequency to 55 Hz. The
noise should be almost undetectable in the graph.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010
2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C
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