Linear DC951A Guide de configuration rapide

dc951af

DEMO MANUAL DC951A

Description

LTC2481

16-Bit ∆Σ ADC with Easy Drive

Input Current Cancellation

and I2C Interface

Demonstration circuit 951Afeatures the LTC2481, a16-Bit

high performance Δ∑ analog-to-digital converter (ADC).

The LTC2481 features 2ppm linearity, 25ppm full-scale

accuracy, 2.5μV offset, and 600nVRMS noise. The input

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 I2C interface.

DC951A is a member of Linear Technology’s QuikEval™

familyof demonstrationboards. Itis designedto alloweasy

evaluation of the LTC2481 and may be connected directly

to the target application’s analog signals while using the

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.

DC590 USB Serial Controller board and supplied software

tomeasure performance.The exposedground 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

Figure 1. Proper Measurement Equipment Setup

Differential

Input

Ribbon

cable To

DC590

Controller

Monitor reference or

external reference

source (See Hardware

Set-up)

Differential

Input

Ribbon

Cable To

DC590

Controller

Monitor reference or

external reference

source (See Hardware

Set-Up)

dc951af

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 evalu-

ation 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 aver-

aged for the DVM display.

Figure 2. Software Screenshot

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.

JP4: Select the source for REF–, either Ground (GND) or

externally supplied.

JP2, JP3: I2CAddress Selection. These pins are connected

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

dc951af

DEMO MANUAL DC951A

HarDware setup

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.

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– RemoveJP2before applyingsignals

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 VCC. While up to a 2MHz clock

can be used, performance may be compromised. Refer

to the LTC2481 data sheet.

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;

anLT1790-5.0 andan LT1236-5. Forapplications usingthe

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 applications. The LT1790 is a good choice for

low power applications or where small size is required.

COMMON 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 func-

tion, connect a stable, low noise, floating voltage source

(with a voltage less than VREF/2) from IN+ to IN– and note

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 bet-

ter 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.

dc951af

DEMO MANUAL DC951A

parts List

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 rejec-

tion, 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

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.)

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.

experiments

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, 04023C103KAT1A

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

dc951af

DEMO MANUAL DC951A

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

scHematic Diagram

D D

C C

B B

A A

2. INSTALL SHUNT ON JP1-JP4 PIN 1 AND 2.

1. ALL RESISTORS ARE IN OHMS, 0402.

NOTES: UNLESS OTHERWISE SPECIFIED

ALL CAPACITORS ARE 0402.

DC951A * LTC2481CDD

Monday, December 05, 2005 1 1

16-BIT DELTA SIGMA ADC WITH PGA AND I2C INTERFACE

KIM T.

MARK T.

SCHEMATIC

SIZE

DATE:

DWG NO. REV

SHEET OF

TITLE:

CONTRACT NO.

APPROVALS

DRAWN:

CHECKED:

APPROVED:

ENGINEER:

DESIGNER:

TECHNOLOGY

Fax: (408)434-0507

Milpitas, CA 95035

Phone: (408)432-1900

1630 McCarthy Blvd.

LTC Confidential-For Customer Use Only

CUSTOMER NOTICE

LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A

CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;

HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO

VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL

APPLICATION. COMPONENT SUBSTITUTION AND PRINTED

CIRUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT

PERFORMANCE OR RELIABILITY. CONTACT LINEAR

TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.

THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND

SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.

VIN

CA0/FO

IN-

IN+

VCC

REF+

REF- SCL

CA1

SDA

VCC

REF-

0.1UF,16V

JP2

CA0/FO

IN+

GND

IN-

4.99K

4.7UF,6.3V

0603

0.1UF,16V

GND

4.99K

CA0/FO

0.01UF

0402

SDASCL

REF+

24LC025

SDA

VCCA0

VSS

SCL

JP4

REF-

EXT

GND

VCC

HD2X7-079-MOLEX

JP1

REF+

LT1236

LT1790

JP3

CA1

LTC2481CDD

1 10

IN+

REF+ CA0/FO

CA1

GND

SDA

VCC

REF-

SCLIN-

GND

LT1790ACS6-5

VIN

VOUTGND1

GND2

4.99K

0.1UF,16V

GND

4.7UF,6.3V

0603

LT1236ACS8-5

8NC

VIN

GNDTRIM

VOUT

1UF,6.3V

0402

dc951af

DEMO MANUAL DC951A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ●FAX: (408) 434-0507 ●www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2013

LT 0613 • PRINTED IN USA

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. LT C 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 LT C applica-

tion engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

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