DC1012A-A - ANALOG DEVICES - Product.Network

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1012A

24-/16-BIT EASY DRIVE 8-/16-CHANNEL DELTA SIGMA ADC WITH I2C INTERFACE

LTC2499CUHF, LTC2497CUHF, LTC2495CUHF

DESCRIPTION

DC1012A-A features the LTC®2499 8/16 channel, 24-

bit ∆Σ

ADC with EasyDrive inputs. 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

LTC2499 also includes an internal temperature sensor

that is accurate to 2 degrees C over the operating

temperature range.

DC1012A-B features the LTC2497 16-bit ADC that is

pinout and software compatible with the LTC2499.

DC1012A-C features the LTC2495 16-bit ADC that

also includes a PGA with a gain range from 1 to 256

and the same temperature sensor as the LTC2499.

DC1012A is a member of Linear Technology‘s

QuickEval™ family of demonstration boards. It is de-

signed to allow easy evaluation of the LTC2499,

LTC2497 or LTC2495. DC1012A may be connected

directly to the target application’s analog signals while

using the DC590A USB Serial Controller board and

supplied software to measure performance. The ex-

posed ground planes allow proper grounding to pro-

totype circuitry. After evaluating with LTC’s software,

the digital signals can be connected to the applica-

tion’s processor / controller for development of the

serial interface.

Design files for this circuit board are available. Call

the LTC factory.

LTC is a registered trademark of Linear Technology Corporation

Figure 1. Proper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1012A

24-/16-BIT EASY DRIVE 8-/16-CHANNEL DELTA SIGMA ADC WITH I2C INTERFACE

QUICK START PROCEDURE

Connect the DC1012A to a DC590A USB Serial Con-

troller using the supplied 14 conductor ribbon ca-

ble. Connect DC590A to host PC with a standard

USB A/B cable. Run the evaluation software sup-

plied with DC590A 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 50/60Hz 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 (LTC2499 and LTC2495

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 1012A

24-/16-BIT EASY DRIVE 8-/16-CHANNEL DELTA SIGMA ADC WITH I2C INTERFACE

HARDWARE SET-UP

JUMPERS

JP1, JP3 – 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.

JP2 – Select source for analog COM input, either

tied to ground or supplied externally to the COM

turret post.

JP4 – JP6 – (CA0-CA2) Address select lines. Lines

may be 1, 0 or floating for a total of 27 different ad-

dresses. The default setting is all 1s.

CONNECTION TO DC590A SERIAL CONTROLLER

J2 is the power and digital interface connector.

Connect to a DC590A 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. Also, if

you are connecting the board to an existing circuit,

the exposed ground planes along the edges of the

board may be used to form a solid connection be-

tween grounds.

GND – Ground turrets are connected directly to the

internal analog ground plane.

PWR GND – Power ground, connected to the power

return trace.

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 DC590A. See the DC590A quick start guide for

details.

REF+, REF- - These turrets are connected to the

LTC2495/2497/2499 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 JP3 are configured for external reference.

Note: The REF+ and REF- terminals are decoupled

to ground with 0.01µF and 4.7 µF capacitors in par-

allel. Thus any source connected to these terminals

must be able to drive a capacitive load and have

very low impedance at DC. Examples are series ref-

erences that require an output capacitor and C-load

stable op amps such as the LT1219 and LT1368.

CH0 – CH15 – These are the differential inputs to

the LTC2499/2497/2495. They may be configured

as single–ended inputs with respect to the COM

pin, or as differential inputs (CH0-1, CH2-3, etc.)

with the polarity software selected.

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. LTC2499 Noise should

be approximately 0.12ppm of 5V (600nV RMS.) The

electrical noise of the LTC2497 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

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1012A

24-/16-BIT EASY DRIVE 8-/16-CHANNEL DELTA SIGMA ADC WITH I2C INTERFACE

be approximately 7.9ppm. The input noise of the

LTC2495 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 140dB+ CMRR of the LTC2499. The

LTC2497 will produce less than 1LSB difference.

INPUT NORMAL MODE REJECTION

The LTC2499 and LTC2495 SINC4 digital filter can

be software selected to reject 50Hz, 60Hz by 110dB,

or both 50 and 60Hz by 87dB. The LTC2497’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 – CH15) to

the same supply through a 10kΩ resistor. Apply a

10Hz, 2V peak-to-peak sine wave to the input

through a 1uF capacitor.

Set the rejection frequency to 55Hz (LTC2499 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 55Hz. The

noise should be almost undetectable in the graph.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1012A

24-/16-BIT EASY DRIVE 8-/16-CHANNEL DELTA SIGMA ADC WITH I2C INTERFACE