TEXAS INSTRUMENTS ADS1244 Technical data

Digital

Filter

Serial

Interface

DRDY/DOUT

SCLK

CLK

AINN

AINP

VREFP VREFN AVDD

GND

DVDD

3rd-Order
Modulator

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A

D

S

1

2

4

4

SBAS273 – DECEMBER 2002

Low-Power, 24-Bit

ANALOG-TO-DIGITAL CONVERTER

ADS1244

FEATURES

● 20-BIT EFFECTIVE RESOLUTION

● CURRENT CONSUMPTION: 90µA

● ANALOG SUPPLY: 2.5V to 5.25V

● DIGITAL SUPPLY: 1.8V to 3.6V

● ±5V DIFFERENTIAL INPUT RANGE

● 0.0002% INL (TYP), 0.0008% INL (MAX)

● SIMPLE 2-WIRE SERIAL INTERFACE

● SIMULTANEOUS 50Hz AND 60Hz REJECTION

● SINGLE CONVERSIONS WITH SLEEP MODE

● SINGLE-CYCLE SETTLING

● SELF-CALIBRATION

● WELL-SUITED FOR MULTICHANNEL SYSTEMS

● EASILY CONNECTS TO THE MSP430

APPLICATIONS

● HAND-HELD INSTRUMENTATION

● PORTABLE MEDICAL EQUIPMENT

● INDUSTRIAL PROCESS CONTROL

● WEIGH SCALES

DESCRIPTION

The ADS1244 is a 24-bit, delta-sigma Analog-to-Digital (A/D)
converter. It offers excellent performance and very low power
in an MSOP-10 package and is well suited for demanding
high-resolution measurements, especially in portable and
other space- and power-constrained systems.

A 3rd-order delta-sigma modulator and digital filter form the
basis of the A/D converter. The analog modulator has a ±5V
differential input range. The digital filter rejects both 50Hz
and 60Hz signals, completely settles in one cycle, and
outputs data at 15 samples per second.

A simple, 2-wire serial interface provides all the necessary
control. Data retrieval, self-calibration, and Sleep Mode are
handled with a few simple waveforms. When only single
conversions are needed, the ADS1244 can be shut down
(Sleep Mode) while idle between measurements to dramati­cally reduce the overall power dissipation. Multiple ADS1244s
can be connected together to create a synchronously sam­pling multichannel measurement system. The ADS1244 is
designed to easily connect to microcontrollers, such as the
MSP430.

The ADS1244 supports 2.5V to 5.25V analog supplies and

1.8V to 3.6V digital supplies. Power is typically less than
270µW in normal operation and less than 1µW during Sleep
Mode.

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.

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.

Copyright © 2002, Texas Instruments Incorporated

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ABSOLUTE MAXIMUM RATINGS

AVDD to GND.......................................................................–0.3V to +6V

DVDD to GND ................................................................... –0.3V to +3.6V

Input Current ............................................................... 100mA, Momentary

Input Current ................................................................ 10mA, Continuous

Analog Input Voltage to GND .............................. –0.5V to AVDD + 0.5V

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

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

Maximum Junction Temperature................................................... +150°C

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

Storage Temperature Range ......................................... –60°C to +150°C

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

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.

(1)

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.

DEMO BOARD ORDERING INFORMATION

PRODUCT DESCRIPTION

ADS1244-EVM ADS1244 Evaluation Module

PACKAGE/ORDERING INFORMATION

PRODUCT PACKAGE-LEAD DESIGNATOR

PACKAGE TEMPERATURE PACKAGE ORDERING TRANSPORT

ADS1244 MSOP-10 DGS –40°C to +85°C BHG ADS1244IDGST Tape and Reel, 250

(1)

SPECIFIED

RANGE MARKING NUMBER MEDIA, QUANTITY

" """"ADS1244IDGSR Tape and Reel, 2500

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

PIN CONFIGURATION

Top View MSOP

GND
VREFP
VREFN

AINN
AINP

1
2
3
4
5

ADS1244

10

9
8
7
6

CLK
SCLK
DRDY/DOUT
DVDD
AVDD

PIN DESCRIPTIONS

PIN

NUMBER NAME DESCRIPTION

1 GND Analog and Digital Ground
2 VREFP Positive Reference Input
3 VREFN Negative Reference Input
4 AINN Negative Analog Input
5 AINP Positive Analog Input
6 AVDD Analog Power Supply, 2.5V to 5.25V
7 DVDD Digital Power Supply, 1.8V to 3.6V
8 DRDY/ Dual-Purpose Output:

DOUT Data Ready: Indicates valid data by going LOW.

Data Output: Outputs data, MSB first, on the first
rising edge of SCLK.

9 SCLK Serial Clock Input: Clocks out data on the rising

edge. Used to initiate calibration and Sleep Mode,
see text for more details.

10 CLK System Clock Input: Typically 2.4576MHz

2

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ADS1244

SBAS273

ELECTRICAL CHARACTERISTICS

All specifications –40°C to +85°C, AVDD = 5V, DVDD = +3V, f

PARAMETER CONDITIONS MIN TYP MAX UNITS
ANALOG INPUT

Full-Scale Input Voltage Range
Absolute Input Range AINP, AINN with Respect to GND GND – 0.1
Differential Input Impedance f

SYSTEM PERFORMANCE

Resolution No Missing Codes 24 Bits
Data Rate f
Integral Nonlinearity (INL) Differential Input Signal, End Point Fit ±0.0002 ±0.0008 % FSR
Offset Error 1 10 ppm of FSR
Offset Error Drift
Gain Error 0.005 0.02 %
Gain Error Drift
Common-Mode Rejection at DC 90 130 dB

Normal-Mode Rejection f

Input Referred Noise 1 ppm of FSR, rms

(3)

(3)

(4)

f

= 50 ± 1Hz, f

CM

f

= 60 ± 1Hz, f

CM

(5)

= 50 ± 1Hz, f

SIG

f

= 60 ± 1Hz, f

SIG

Analog Power-Supply Rejection at DC, ∆AVDD = 5% 105 dB
Digital Power-Supply Rejection at DC, ∆DVDD = 5% 100 dB

VOLTAGE REFERENCE INPUT

Reference Input Voltage (V
Negative Reference Input (VREFN) GND – 0.1 VREFP – 0.5 V

)V

REF

REF

Positive Reference Input (VREFP) VREFN + 0.5 AVDD + 0.1 V
Voltage Reference Impedance f

DIGITAL INPUT/OUTPUT

Logic Levels

V

(CLK, SCLK) 2.1 5.25 V

IH

V

(CLK, SCLK) GND 0.9 V

IL

V

(

DRDY/DOUT

OH

V

(

DRDY/DOUT

OL

Input Leakage (CLK, SCLK) 0 < (CLK, SCLK) < DVDD ±10 µA
CLK Frequency (f
CLK Duty Cycle 30 70 %

)I

)I

) 6MHz

CLK

POWER SUPPLY

AVDD 2.5 5.25 V
DVDD 1.8 3.6 V
AVDD Current Sleep Mode 0.1 1 µA

DVDD Current Sleep Mode, CLK Stopped 0.1 µA

Sleep Mode, 2.4576MHz CLK Running 1.3 5 µA

Total Power Dissipation AVDD = DVDD = 3V 270 µW

NOTES: (1) sps = Samples Per Second. (2) FSR = Full-Scale Range = 4V
of the common-mode input. (5) f

is the frequency of the input signal. (6) It will not be possible to reach the digital output full-scale code when V

SIG

= 2.4576MHz, and V

CLK

= 2.5V, unless otherwise specified.

REF

ADS1244

AINP – AINN

= 2.4576MHz 5 MΩ

CLK

= 2.4576MHz 15 sps

CLK

±2V

REF

AVDD + 0.1

0.01 ppm of FSR/°C

0.5 ppm/°C

= 2.4576MHz 100 dB

CLK

= 2.4576MHz 100 dB

CLK

= 2.4576MHz 60 dB

CLK

= 2.4576MHz 70 dB

CLK

≡ VREFP – VREFN 0.5 2.5 AVDD

= 2.4576MHz 1 MΩ

CLK

= 1mA 2.6 V

OH

= 1mA 0.4 V

OL

(6)

AVDD = 3V 85 µA
AVDD = 5V 90 150 µA

DVDD = 3V

. (3) Recalibration can reduce these errors to the level of the noise. (4) fCM is the frequency

REF

4.5 10 µA

REF

V
V

(1)

V

> AVDD/2.

(2)

ADS1244

SBAS273

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TYPICAL CHARACTERISTICS

At TA = +25°C, AVDD = +5V, DVDD = +3V, f

= 2.4576MHz, and V

CLK

= +2.5V, unless otherwise specified.

REF

110
105

12

10

100

ANALOG CURRENT vs TEMPERATURE

95

AVDD = 5V, f

90
85

Current (µA)

= 4.9152MHz

CLK

8

6

Current (µA)

4

DIGITAL CURRENT vs TEMPERATURE

DVDD = 3V, f

= 4.9152MHz

CLK

80
75

AVDD = 3V, f

70

15–5–25 35 55 75 95–45

Temperature (°C)

ANALOG CURRENT vs ANALOG SUPPLY

94

92

90

f

= 4.9152MHz

CLK

88

86

Current (µA)

84

82

80

3 3.5 4

Analog Supply (V)

= 2.4576MHz

CLK

f

CLK

4.5 5

= 2.4576MHz

2

DVDD = 1.8V, f

= 2.4576MHz

CLK

0

15–5–25 35 55 75 95–45

Temperature (°C)

DIGITAL CURRENT vs DIGITAL SUPPLY

20
18
16
14
12
10

f

= 4.9152MHz

CLK

8

Current (µA)

6
4
2
0

5.52.5

2 2.5 3

f

= 2.4576MHz

CLK

3.5

41.5

Digital Supply (V)

INL (ppm of FSR)

4

3

2

T = 25°C

AVDD = 5V, V

1

0

–1

INTEGRAL NONLINEARITY vs V

–2

T = 85°C

–3

IN

T = –40°C

REF

= 2.5V

3

2

1

0

–1

INL (ppm of FSR)

–2

T = 85°C

–3

1–1–335–5

VIN (V)

INTEGRAL NONLINEARITY vs V

AVDD = 3V, V

T = –40°C

T = 25°C

0.5–0.5–1.5 1.5 2.5–2.5

VIN (V)

IN

REF

= 1.25V

ADS1244

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SBAS273

TYPICAL CHARACTERISTICS (Cont.)

INTEGRAL NONLINEARITY vs ANALOG SUPPLY

Analog Supply (V)

INL (ppm of FSR)

1.5 2 2.5 3 3.5 4 4.5 5 5.5

20
18
16
14
12
10

8
6
4
2
0

T = 25°C

T = 85°C

T = –40°C

V

REF

= AVDD/2

GAIN vs TEMPERATURE

Temperature (°C)

Normalized Gain

15–5–25 35 55 75 95–45

1.00008

1.00006

1.00004

1.00002
1

0.99998

0.99996

0.99994

0.99992

0.9999

NOISE vs TEMPERATURE

Temperature (°C)

Noise (ppm of FSR, rms)

–25 –515

35 55 75

95–45

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2
0

At TA = +25°C, AVDD = +5V, DVDD = +3V, f

INTEGRAL NONLINEARITY vs ANALOG SUPPLY

20
18
16
14
12
10

8

INL (ppm of FSR)

6
4
2
0

1.5 2 2.5 3 3.5 4 4.5 5 5.5

T = –40°C

T = 85°C

Analog Supply (V)

= 2.4576MHz, and V

CLK

T = 25°C

V

REF

= AVDD

= +2.5V, unless otherwise specified.

REF

1

0.5

0

–0.5

Normalized Offset (ppm of FSR)

–1

1.6

1.5

1.4

1.3

1.2

1.1
1

0.9

Noise (ppm of FSR, rms)

0.8

0.7

0.6

ADS1244

SBAS273

OFFSET vs TEMPERATURE

Temperature (°C)

NOISE vs INPUT SIGNAL

–3 –11

15–5–25 35 55 75 95–45

3

V

(V)

IN

5–5

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TYPICAL CHARACTERISTICS (Cont.)

At TA = +25°C, AVDD = +5V, DVDD = +3V, f

= 2.4576MHz, and V

CLK

= +2.5V, unless otherwise specified.

REF

1200

1000

800

600

400

Number of Occurences

200

0

–3 –2 –10 1 2 3 4–4

120

100

80

60

HISTOGRAM OF OUTPUT DATA

ppm of FSR

ANALOG PSRR vs FREQUENCY

14
13
12
11
10

Input-Referred Noise (µV, rms)

120

100

80

60

INPUT-REFERRED NOISE vs V

9
8
7
6

V

(V)

REF

DIGITAL PSRR vs FREQUENCY

REF

321450

Magnitude (dB)

40

20

0

1k10010 10k 100k1

Frequency (Hz)

160
140
120
100

80
60

Magnitude (dB)

40
20

0

Magnitude (dB)

40

20

0

CMRR vs FREQUENCY

1k10010 10k 100k1

Frequency (Hz)

1k10010 10k 100k1

Frequency (Hz)

6

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ADS1244

SBAS273