TEXAS INSTRUMENTS ADS1251 Technical data

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A

D

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SBAS184A – MARCH 2001 – REVISED SEPTEMBER 2003

24-Bit, 20kHz, Low-Power

ANALOG-TO-DIGITAL CONVERTER

ADS1251

FEATURES

● 24 BITS—NO MISSING CODES

● 19 BITS EFFECTIVE RESOLUTION UP TO

20kHz DATA RATE

● LOW NOISE: 1.5ppm

● DIFFERENTIAL INPUTS

● INL: 15ppm (max)

● EXTERNAL REFERENCE (0.5V to 5V)

● POWER-DOWN MODE

● SYNC MODE

● LOW POWER: 8mW at 20kHz

5mW at 10kHz

APPLICATIONS

● CARDIAC DIAGNOSTICS

● DIRECT THERMOCOUPLE INTERFACES

● BLOOD ANALYSIS

● INFRARED PYROMETERS

● LIQUID/GAS CHROMATOGRAPHY

● PRECISION PROCESS CONTROL

DESCRIPTION

The ADS1251 is a precision, wide dynamic range, delta­sigma, Analog-to-Digital (A/D) converter with 24-bit resolu­tion operating from a single +5V supply. The delta-sigma
architecture features wide dynamic range, and 24 bits of no
missing code performance. Effective resolution of 19 bits
(1.5ppm of rms noise) is achieved at conversion rates up to
20kHz.

The ADS1251 is designed for high-resolution measurement
applications in cardiac diagnostics, smart transmitters, indus­trial process control, weigh scales, chromatography, and
portable instrumentation. The converter includes a flexible,
2-wire synchronous serial interface for low-cost isolation.

The ADS1251 is a single-channel converter and is offered in
an SO-8 package. It is pin-compatible with the faster ADS1252
(41.7kHz data rate).

ADS1251

+V

IN

–V

IN

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.

4th-Order

∆Σ

Modulator

Digital

Filter

www.ti.com

Serial

Interface

Control

V

REF

CLK

SCLK
DOUT/DRDY

+V

DD

GND

Copyright © 2001-2003, Texas Instruments Incorporated

ABSOLUTE MAXIMUM RATINGS

Analog Input: Current ............................................... ±100mA, Momentary

V

to GND ............................................................................ –0.3V to 6V

DD

V

REF

Digital Input Voltage to GND ................................... –0.3V to V

Digital Output Voltage to GND .................................–0.3V to V

Operating Temperature ...................................................... –40°C to 85°C

Lead Temperature (soldering, 10s).............................................. +300°C

Power Dissipation .......................................................................... 500mW

NOTE: (1) Stresses above those listed under “Absolute Maximum Ratings”
may cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.

Voltage .................................... GND – 0.3V to V

Voltage to GND ............................................... –0.3V to VDD + 0.3V

(1)

±10mA, Continuous

+ 0.3V

DD

+ 0.3V

DD

+ 0.3V

DD

ELECTROSTATIC
DISCHARGE SENSITIVITY

This integrated circuit can be damaged by ESD. Texas
Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper han­dling and installation procedures can cause damage.

ESD damage can range from subtle performance degrada­tion to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.

PACKAGE/ORDERING INFORMATION

PRODUCT PACKAGE-LEAD DESIGNATOR

PACKAGE TEMPERATURE PACKAGE ORDERING TRANSPORT

ADS1251 SO-8 D –40°C to +85°C ADS1251U ADS1251U Rails, 100

(1)

SPECIFIED

RANGE MARKING NUMBER MEDIA, QUANTITY

" """"ADS1251U/2K5 Tape and Reel, 2500

NOTE: (1) For the most current specifications and package information, refer to our web site at www.ti.com.

PRODUCT FAMILY

PRODUCT # OF INPUTS MAXIMUM DATA RATE COMMENTS

ADS1250 1 Differential 25.0kHz Includes PGA from 1 to 8
ADS1251 1 Differential 26.8kHz
ADS1252 1 Differential 41.7kHz
ADS1253 4 Differential 20.8kHz
ADS1254 4 Differential 20.8kHz Includes Separate Analog and Digital Supplies

ELECTRICAL CHARACTERISTICS

All specifications at T

PARAMETER CONDITIONS MIN TYP MAX UNITS
ANALOG INPUT

Full-Scale Input Voltage +V
Absolute Input Voltage +V
Differential Input Impedance CLK = 3.84kHz 430 MΩ

Input Capacitance 6pF
Input Leakage At +25°C550pA

DYNAMIC CHARACTERISTICS

Data Rate 20.8 kHz
Bandwidth –3dB, CLK = 8MHz 4.24 kHz
Serial Clock (SCLK) 8MHz
System Clock Input (CLK) 8MHz

ACCURACY

Integral Nonlinearity Differential Input ±0.0002 ±0.0015 % of FSR
THD 1kHz Input; 0.1dB below FS 105 dB

Noise 1.5 2.5 ppm of FSR, rms
Resolution 24 Bits
No Missing Codes 24 Bits
Common-Mode Rejection 60Hz, AC 90 98 dB
Gain Error 0.1 1 % of FSR
Offset Error ±30 ±100 ppm of FSR
Gain Sensitivity to V
Power-Supply Rejection Ratio 70 80 dB

PERFORMANCE OVER TEMPERATURE

Offset Drift 0.07 ppm/°C
Gain Drift 0.4 ppm/°C

MIN

REF

to T

, VDD = +5V, CLK = 8MHz, and V

MAX

= 4.096, unless otherwise specified.

REF

ADS1251U

– (–VIN) ±V

IN

or –VIN to GND –0.3 V

IN

CLK = 1MHz 1.7 MΩ
CLK = 8MHz 210 kΩ

to T

At T

MIN

MAX

REF

DD

1nA

1:1

V
V

2

www.ti.com

ADS1251

SBAS184A

ELECTRICAL CHARACTERISTICS (Cont.)

All specifications at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

VOLTAGE REFERENCE

V

REF

Load Current 32 µA

DIGITAL INPUT/OUTPUT

Logic Family CMOS
Logic Level: V

Input (SCLK, CLK) Hysteresis 0.6 V
Data Format

POWER-SUPPLY REQUIREMENTS

Operation +4.75 +5 +5.25 VDC
Quiescent Current V
Operating Power 7.5 10 mW
Power-Down Current 0.4 1 µA

TEMPERATURE RANGE

Operating –40 +85 °C
Storage –60 +100 °C

to T

MIN

, VDD = +5V, CLK = 8MHz, and V

MAX

= 4.096, unless otherwise specified.

REF

ADS1251U

0.5 4.096 V

IH

V

IL

V

OH

V

OL

IOH = –500µA +4.5 V

IOL = 500µA 0.4 V

+4.0 +VDD + 0.3 V
–0.3 +0.8 V

DD

Offset Binary Two’s Complement

= +5VDC 1.5 2 mA

DD

V

PIN CONFIGURATION

Top View SO

+V

–V

+V

CLK

1

IN

2

IN

ADS1251U

3

DD

4

V

8

REF

7

GND

SCLK

6

5

DOUT/DRDY

PIN DESCRIPTIONS

PIN NAME PIN DESCRIPTION

1+V

2–V

3+V

IN

IN

DD

4 CLK Digital Input: Device System Clock. The

5

DOUT/DRDY

6 SCLK Digital Input: Serial Clock. The serial clock

7 GND Input: Ground
8V

REF

Analog Input: Positive Input of the Differen­tial Analog Input

Analog Input: Negative Input of the Differ­ential Analog Input.

Input: Power-Supply Voltage, +5V

system clock is in the form of a CMOS­compatible clock. This is a Schmitt-Trigger
input.

Digital Output: Serial Data Output/Data
Ready. This output indicates that a new
output word is available from the ADS1251
data output register. The serial data is
clocked out of the serial data output shift
register using SCLK.

is in the form of a CMOS-compatible clock.
The serial clock operates independently
from the system clock, therefore, it is pos­sible to run SCLK at a higher frequency
than CLK. The normal state of SCLK is
LOW. Holding SCLK HIGH will either ini­tiate a modulator reset for synchronizing
multiple converters or enter power-down
mode. This is a Schmitt-Trigger input.

Analog Input: Reference Voltage Input

ADS1251

SBAS184A

www.ti.com

3

TYPICAL CHARACTERISTICS

At TA = +25°C, VDD = +5V, CLK = 8MHz, and V

= 4.096, unless otherwise specified.

REF

2.0

1.6

1.2

0.8

RMS Noise (ppm of FS)

0.4

0

2.0

1.8

1.6

10010 10k1k 100k

RMS NOISE vs TEMPERATURE

RMS NOISE vs DATA RATE

Data Rate (Hz)

EFFECTIVE RESOLUTION vs DATA OUTPUT RATE

20.0

19.5

19.0

18.5

Effective Resolution (Bits)

18.0

19.5

19.0

EFFECTIVE RESOLUTION vs TEMPERATURE

1k100 10k 100k

Data Output Rate (Hz)

1.4

RMS Noise (ppm of FS)

1.2

1.0
–40 –20 0 20 40 60 80 100

Temperature (°C)

18
16
14
12
10

8
6

RMS Noise (µV)

4
2
0

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

RMS NOISE vs V

V

REF

VOLTAGE

REF

Voltage (V)

18.5

Effective Resolution (Bits)

18.0
–40 –20 0 20 40 60 80 100

Temperature (°C)

14

12

10

8

6

4

RMS Noise (ppm of FS)

2

0

012345

RMS NOISE vs V

V

REF

VOLTAGE

REF

Voltage (V)

4

www.ti.com

ADS1251

SBAS184A

TYPICAL CHARACTERISTICS (Cont.)

40
35
30
25
20
15
10

5
0

OFFSET vs TEMPERATURE

Temperature (°C)

–40 –20 0 20 40 60 80 100

Offset (ppm of FS)

–60
–65
–70
–75
–80
–85
–90
–95

–100

POWER-SUPPLY REJECTION RATIO

vs CLK FREQUENCY

Clock Frequency (MHz)

12345678

PSRR (dB)

At TA = +25°C, VDD = +5V, CLK = 8MHz, and V

= 4.096, unless otherwise specified.

REF

2.0

1.5

1.0

0.5

RMS Noise (ppm of FS)

0

–5 –4 –3 –2 –10 1 23 4 5

INTEGRAL NONLINEARITY vs DATA OUTPUT RATE

5

4

3

RMS NOISE vs INPUT VOLTAGE

Input Voltage (V)

4.0

3.5

3.0

2.5

2.0

1.5

INL (ppm of FS)

1.0

0.5

INTEGRAL NONLINEARITY vs TEMPERATURE

0

–40 –20 0 20 40 60 80 100

Temperature (°C)

2

INL (ppm of FS)

1

0

100 1k 10k 100k

Data Output Rate (Hz)

650

625

600

575

550

Gain Error (ppm of FS)

525

500

–40 –20 0 20 40 60 80 100

ADS1251

SBAS184A

GAIN ERROR vs TEMPERATURE

Temperature (°C)

www.ti.com

5

TYPICAL CHARACTERISTICS (Cont.)

At TA = +25°C, VDD = +5V, CLK = 8MHz, and V

= 4.096, unless otherwise specified.

REF

COMMON-MODE REJECTION RATIO

–60
–65
–70
–75
–80
–85
–90

CMRR at 60Hz (dB)

–95
–100
–105

12345678

1.65

1.60

1.55

1.50

Current (mA)

1.45

1.40
–40 –20 0 20 40 60 80 100

vs CLK FREQUENCY

Clock Frequency (MHz)

CURRENT vs TEMPERATURE

Temperature (°C)

COMMON-MODE REJECTION RATIO

–60
–65
–70
–75
–80
–85

CMRR (dB)

–90

–95
–100
–105

10 100 1k 10k 100k

9
8
7
6
5
4
3
2

Power Dissipation (mW)

1
0

012345 768

vs COMMON-MODE FREQUENCY

Common-Mode Signal Frequency (Hz)

POWER DISSIPATION vs CLK FREQUENCY

Clock Frequency (MHz)

V

CURRENT vs CLK FREQUENCY

35

30

25

20

15

Current (µA)

REF

V

10

5

0

0.1 1 10

6

REF

Clock Frequency (MHz)

www.ti.com

0

–20
–40
–60

–80
–100
–120

Relative Magnitude (dB)

–140
–160

01234567891011

(1kHz input at 0.1dB less than full-scale)

TYPICAL FFT

Frequency (kHz)

ADS1251

SBAS184A