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Description
DEMO MANUAL DC951A
LTC2481
16-Bit ∆Σ ADC with Easy Drive
Input Current Cancellation
and I
2
C Interface
Demonstration circuit 951A features the LTC2481, a 16-Bit
high performance Δ∑ analog-to-digital converter (ADC).
The LTC2481 features 2ppm linearity, 25ppm full-scale
accuracy, 2.5μV offset, and 600nV
is fully differential, with input common mode rejection of
140dB. The LTC2481 is available in a 10-pin DFN package
and has an easy to use I
DC951A is a member of Linear Technology’s QuikEval™
family of demonstration boards. It is designed to allow easy
evaluation of the LTC2481 and may be connected directly
to the target application’s analog signals while using the
Monitor reference or
Monitor reference or
external reference
external reference
source (See Hardware
source (See Hardware
Set-up)
Set-Up)
Differential
Differential
Input
Input
2
C interface.
noise. The input
RMS
DC590 USB Serial Controller board and supplied software
to measure performance. The exposed ground planes allow
proper grounding to prototype circuitry. After evaluating
with Linear Technology’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.
Ribbon
Ribbon
cable To
Cable To
DC590
DC590
Controller
Controller
Figure 1. Proper Measurement Equipment Setup
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DEMO MANUAL DC951A
Quick start proceDure
Connect DC951A 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 evaluation software supplied with DC590 or downloaded from
http://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
documented 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 averaged for the DVM display.
HarDware setup
CONNECTION TO DC590 SERIAL CONTROLLER
J1 is the power and digital interface connector. Connect
to DC590 serial controller with supplied 14-conductor
ribbon cable.
JUMPERS
JP1: Select the source for REF+, either an LT1236A-5, an
LT1790-5, or externally supplied if JP1 is removed.
2
Figure 2. Software Screenshot
JP4: Select the source for REF–, either Ground (GND) or
externally supplied.
JP2, JP3: I
to CA0/F0 and CA1, respectively. Refer to the LTC2481
data sheet for address mapping.
ANALOG CONNECTIONS
Analog signal connections are made via the row of turret
posts along the edge of the board. Also, when connecting
2
C Address Selection. These pins are connected
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HarDware setup
DEMO MANUAL DC951A
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: Three ground turrets are connected directly to the
internal ground planes.
VCC: This is the supply for the ADC. Do not draw any
power from this point.
REF+: Connected to the LTC2481 reference pin. If the
onboard reference is being used, the reference voltage
may be monitored from this point. An external reference
may be connected to these terminals if JP1 is removed.
experiments
INPUT NOISE
One of the characteristics of the LTC2481 is that the
600nV input noise floor is far below the quantization level
of 38µV when a 5V reference is used and the PGA is set
to a gain of 1. This means that the output will be stable if
the input noise level is significantly below 38µV. In this
sense, the LTC2481 is a true 17 effective bit part, whereas
many 16-bit SAR converters have several LSBs of noise.
Solder a short wire from the IN– turret post to the IN+
turret post. Noise should be below the quantization level
of the LTC2481. This will result in a noise reading of zero
on the control software.
Increase the gain setting to 256 (1× speed mode.) This
results in a 149nV LSB size, allowing a true measurement
of the input noise. Tw o references are included on DC951A;
an LT1790-5.0 and an LT1236-5. For applications using the
lower gain settings, the LT1790 is adequate. However, in
the highest gain settings the LT1790 can elevate the input
noise by a factor of 2 or 3. The LT1236 is significantly
quieter than the LT1790 and is a good choice for very high
resolution
low power applications or where small size is required.
applications. The LT1790 is a good choice for
REF–: Connected to the LTC2481 REF– pin. Normally at
ground when JP4 is set to GND.
IN+, IN–: These are the differential inputs to the LTC2481.
CA0/F0: IMPORTANT – Remove JP2 before applying signals
to this turret. An external conversion clock may be applied
to the CA0/F0 turret to modify the frequency rejection
characteristics or data output rate of the LTC2481. This
should be a square wave with a low level equal to ground
and a high level equal to V
can be used, performance may be compromised. Refer
to the LTC2481
CO
MMON MODE REJECTION
Tie the two inputs (still connected together) to ground
through a short wire and note the indicated voltage. Tie
the inputs to REF+; the difference should be less than
0.5μV due to the 140dB minimum CMRR of the LTC2481.
BIPOLAR SYMMETRY
To demonstrate the symmetry of the ADCs transfer function, connect a stable, low noise, floating voltage source
(with a voltage less than V
the indicated voltage. Reverse the polarity; the indicated
voltage will typically be within one LSB of the first reading
multiplied by –1.
One convenient voltage source for this experiment is a
single alkaline battery. While a battery has fairly low noise,
it is sensitive to temperature drift. It is best to use a large
(D-size) battery that is insulated from air currents. A better source is a battery powered series reference such as
the LT1790. This part is available with output voltages of
1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V and 5V.
data sheet.
. While up to a 2MHz clock
CC
/2) from IN+ to IN– and note
REF
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DEMO MANUAL DC951A
experiments
INPUT NORMAL MODE REJECTION
The LTC2481’s SINC4 digital filter is trimmed to reject
50Hz or 60Hz line noise when operated with the internal
conversion clock. To measure input normal mode rejection, connect IN– to a 2.5V source such as an LT1790-2.5
reference or 1k – 1k divider from the onboard 5V reference
to ground. Apply a 10Hz, 2V peak-to-peak sine wave to IN+
through a 1µF capacitor. No DC bias is required because
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 60Hz (or 50Hz or
55Hz, depending on the selected rejection frequency.) The
noise should be almost undetectable in the graph. Note
that the indicated noise in ppm may still be above that of
the data sheet specification because the inputs are not
connected to a DC source.
the 2MΩ to 3MΩ input impedance of the LTC2481 tends
to self-bias the input to mid-reference (see data sheet
applications information for details.)
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 3 C1, C6, C7 CAP., X7R 0.1µF 16V, 20%, 0402 TDK, C1005X7R1C104M
2 2 C2, C3 CAP., X5R 4.7µF 6.3V, 20%, 0603 TDK, C1608X5R0J475M
3 1 C4 CAP., X5R, 1µF 6.3V, 20%, 0402 TDK, C1005X5R0J105M
4 1 C5 CAP., X7R 0.01µF 25V, 10%, 0402 AVX, 04023C103K AT1A
5 9 E1-E9 TESTPOINT, TURRET, 0.064" MILL-MAX, 2308-2
6 4 JP1, JP2, JP3, JP4 JMP, 3 PIN 1 ROW 0.079CC SAMTEC, TMM-103-02-L-S
7 4 SHUNTS FOR JP1-JP4 PIN 1 & 2 SHUNT, 0.079" CENTER SAMTEC, 2SN-BK-G
8 1 J1 HEADER, 2X7 PIN, 0.079CC MOLEX, 87331-1420
9 3 R1, R3, R4 RES., CHIP 4.99k 1/16W 1%, 0402 AAC, CR05-4991FM
10 1 R2 RES., CHIP 1 1/16W 5%, 0402 AAC, CR05-1R0JM
11 1 U1 I.C., LTC2481CDD, DFN10DD LINEAR TECH., LTC2481CDD
12 1 U2 I.C., LT1790ACS6-5, SOT23-6 LINEAR TECH., LT1790ACS6-5
13 1 U3 I.C., 24LC025, TSSOP8 MICROCHIP, 24LC025-I/ST
14 1 U4 I.C., LT1236ACS8-5, SO8 LINEAR TECH., LT1236ACS8-5
4
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scHematic Diagram
1
2
DEMO MANUAL DC951A
A
GND
CA0/FO
E7
E8
J1
1
0
JP2
CA0/FO
VCC
342
1
1
VIN
JP3
VCC
5
342
VCC
SDA
1
0
CA1
8
5
6
7
8
9
6
7
R4
4.99K
C6
0.1UF,16V
U3
SDASCL
9
1%
24LC025
10
10
81
VCCA0
12
11
12
11
R3
4.99K
1%
R1
4.99K
1%
7
6
WP
SCL
A1A2VSS
234
13
14
13
14
HD2X7-079-MOLEX
Fax: (408)434-0507
Milpitas, CA 95035
Phone: (408)432-1900
1630 McCarthy Blvd.
LTC Confidential-For Customer Use Only
TECHNOLOGY
5
SDA
SCHEMATIC
16-BIT DELTA SIGMA ADC WITH PGA AND I2C INTERFACE
TITLE:
KIM T.
APPROVALS
CONTRACT NO.
DRAWN:
CHECKED:
APPROVED:
SHEET OF
1
DC951A * LTC2481CDD
Monday, December 05, 2005 1 1
DWG NO. REV
A
2
SIZE
DATE:
MARK T.
ENGINEER:
DESIGNER:
C7
0.1UF,16V
1
2
3
45
3
U4
4
5
GNDTRIM
678
NC
VIN
VOUTNCNC
R2
1
NC
LT1236ACS8-5
C2
4.7UF,6.3V
0603
U2
LT1790ACS6-5
JP1
REF+
LT1236
LT1790
C1
0.1UF,16V
VIN
NC
4.7UF,6.3V
0603
NC
GND2
VOUTGND1
4
5
61
C3
CA0/FO
CA1
987
65
CA1
SCLIN-
SDA
3
2
U1
LTC2481CDD
C5
0.01UF
0402
C4
1UF,6.3V
0402
VCC
GND
GND
11
IN+
REF+ CA0/FO
VCC
REF-
4
1 10
2
3
IN-
IN+
REF+
REF- SCL
JP4
REF-
EXT
GND
CUSTOMER NOTICE
CIRUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
ALL CAPACITORS ARE 0402.
NOTES: UNLESS OTHERWISE SPECIFIED
E3
E4
E1
E2
GND
VCC
E9
REF+
E5
E6
IN+
IN-
REF-
GND
1. ALL RESISTORS ARE IN OHMS, 0402.
3
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
4
5
2. INSTALL SHUNT ON JP1-JP4 PIN 1 AND 2.
D D
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
C C
B B
A A
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DEMO MANUAL DC951A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LT C ) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LT C for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LT C from all claims
arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LT C currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
Linear Technology Corporation
6
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
dc951af
LT 0613 • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2013
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