LINEAR TECHNOLOGY LTC2485 Technical data

Input Current Cancellation and I

FEATURES

■

Easy DriveTM Technology Enables Rail-to-Rail
Inputs with Zero Differential Input Current

■

Directly Digitizes High Impedance Sensors with
Full Accuracy

■

Integrated Temperature Sensor

■

GND to VCC Input/Reference Common Mode Range

■

2-Wire I2C Interface

■

Programmable 50Hz, 60Hz or Simultaneous
50Hz/60Hz Rejection Mode

■

2ppm (0.25LSB) INL, No Missing Codes

■

1ppm Offset and 15ppm Full-Scale Error

■

Selectable 2x Speed Mode

■

No Latency: Digital Filter Settles in a Single Cycle

■

Single Supply 2.7V to 5.5V Operation

■

Internal Oscillator

■

Six Addresses Available and One Global Address for
Synchronization

■

Available in a Tiny (3mm × 3mm) 10-Lead
DFN Package

U

APPLICATIO S

■

Direct Sensor Digitizer

■

Weight Scales

■

Direct Temperature Measurement

■

Strain Gauge Transducers

■

Instrumentation

■

Industrial Process Control

■

DVMs and Meters

LTC2485

24-Bit ∆Σ ADC with Easy Drive

2

C Interface

U

DESCRIPTIO

®

The LTC
analog-to-digital converter with patented Easy Drive tech­nology and I
scheme eliminates dynamic input current errors and the
shortcomings of on-chip buffering through automatic
cancellation of differential input current. This allows large
external source impedances and input signals, with rail-to­rail input range to be directly digitized while maintaining
exceptional DC accuracy.

The LTC2485 includes on-chip temperature sensor and an
oscillator. The LTC2485 can be configured through an I
interface to measure an external signal or internal tem­perature sensor and reject line frequencies. 50Hz, 60Hz or
simultaneous 50Hz/60Hz line frequency rejection can be
selected as well as a 2x speed-up mode.

The LTC2485 allows a wide common mode input range
(0V to VCC) independent of the reference voltage. The
reference can be as low as 100mV or can be tied directly
to V
lator eliminating the need for external crystals or oscilla­tors. Absolute accuracy and low drift are automatically
maintained through continuous, transparent, offset and
full-scale calibration.

No Latency ∆Σ and Easy Drive are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.

2485 combines a 24-bit plus sign No Latency ∆Σ

2

C digital interface. The patented sampling

. The LTC2485 includes an on-chip trimmed oscil-

CC

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

TM

2

C

TYPICAL APPLICATIO

V

CC

SENSE

10k

10k

= 0

I

DIFF

1µF

V

IN

V

IN

REF+V

+

LTC2485

–

GND

REF

U

1µF

SCL

SDA

CA0/F

CA1

2485 TA01

2-WIRE

2

I

C INTERFACE

0

6 ADDRESSES

CC

–

+FS Error vs R

80

VCC = 5V

= 5V

V

REF

60

+

= 3.75V

V

IN

–

= 1.25V

V

IN

40

= GND

F

O

= 25°C

T

A

20

0

–20

+FS ERROR (ppm)

–40

–60

–80

10 100 10k

1

SOURCE

CIN = 1µF

R

SOURCE

at IN+ and IN

1k

(Ω)

–

100k

2485 TA02

2485fa

1

LTC2485

TOP VIEW

11

DD PACKAGE

10-LEAD (3mm × 3mm) PLASTIC DFN

10

9

6

7

8

4

5

3

2

1

CA0/F

0

CA1

GND

SDA

SCL

REF

+

V

CC

REF

–

IN

+

IN

–

WWWU

ABSOLUTE AXI U RATI GS

(Notes 1, 2)

Supply Voltage (VCC) to GND...................... –0.3V to 6V

Analog Input Voltage to GND ....... –0.3V to (V

Reference Input Voltage to GND .. – 0.3V to (V

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

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

Operating Temperature Range

LTC2485C ................................................... 0°C to 70°C

LTC2485I ................................................ – 40°C to 85°C

Storage Temperature Range ................ –65°C to 125°C

+ 0.3V)

CC

+ 0.3V)

CC

+ 0.3V)

CC

+ 0.3V)

CC

UU

W

PACKAGE/ORDER I FOR ATIO

T

= 125°C, θJA = 43°C/ W

JMAX

EXPOSED PAD (PIN 11) IS GND

MUST BE SOLDERED TO PCB

ORDER PART NUMBER

LTC2485CDD
LTC2485IDD

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts specified with wider operating temperature ranges.
*The temperature grade is identified by a label on the shipping container.

DD PART MARKING*

LBST

ELECTRICAL CHARACTERISTICS ( OR AL SPEED)

apply over the full operating temperature range, otherwise specifications are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Resolution (No Missing Codes) 0.1 ≤ V
Integral Nonlinearity 5V ≤ VCC ≤ 5.5V, V

Offset Error 2.5V ≤ V
Offset Error Drift 2.5V ≤ V
Positive Full-Scale Error 2.5V ≤ V
Positive Full-Scale Error Drift 2.5V ≤ V

Negative Full-Scale Error 2.5V ≤ V
Negative Full-Scale Error Drift 2.5V ≤ V

Total Unadjusted Error 5V ≤ VCC ≤ 5.5V, V

Output Noise 5V ≤ VCC ≤ 5.5V, V
Internal PTAT Signal TA = 27°C 420 mV
Internal PTAT Temperature Coefficient 1.4 mV/°C

2

UW

The ● denotes the specifications which

= 25°C. (Notes 3, 4)

A

≤ VCC, –FS ≤ VIN ≤ +FS (Note 5)

REF

= 5V, V

2.7V ≤ VCC ≤ 5.5V, V

REF

REF

REF

REF

REF

REF

5V ≤ VCC ≤ 5.5V, V

2.7V ≤ VCC ≤ 5.5V, V

REF

= 2.5V, V

REF

≤ VCC, GND ≤ IN+ = IN– ≤ VCC (Note 13)
≤ VCC, GND ≤ IN+ = IN– ≤ V
≤ VCC, IN+ = 0.75V
≤ VCC, IN+ = 0.75V

≤ VCC, IN– = 0.75V
≤ VCC, IN– = 0.75V

= 2.5V, V

REF

= 5V, V

REF

= 2.5V, V

REF

= 5V, GND ≤ IN– = IN+ ≤ VCC (Note 12) 0.6 µV

REF

= 2.5V (Note 6)

IN(CM)

IN(CM)

= 1.25V (Note 6) 1 ppm of V

IN(CM)

CC

, IN– = 0.25V

REF

, IN– = 0.25V

REF

, IN+ = 0.25V

REF

, IN+ = 0.25V

REF

= 1.25V (Note 6) 15 ppm of V

IN(CM)

REF

REF

REF

REF

= 2.5V (Note 6) 15 ppm of V

= 1.25V (Note 6) 15 ppm of V

IN(CM)

●

24 Bits

●

●

2 10 ppm of V

0.5 2.5 µV
10 nV/°C

●

25 ppm of V

0.1 ppm of

●

25 ppm of V

0.1 ppm of

V

V

REF

REF

RMS

2485fa

REF
REF

REF

/°C

REF

/°C

REF

REF
REF

LTC2485

ELECTRICAL CHARACTERISTICS (2x SPEED)

full operating temperature range, otherwise specifications are at T

= 25°C. (Notes 3, 4)

A

The ● denotes the specifications which apply over the

PARAMETER CONDITIONS MIN TYP MAX UNITS

Resolution (No Missing Codes) 0.1 ≤ V
Integral Nonlinearity 5V ≤ VCC ≤ 5.5V, V

2.7V ≤ VCC ≤ 5.5V, V
Offset Error 2.5V ≤ V
Offset Error Drift 2.5V ≤ V
Positive Full-Scale Error 2.5V ≤ V
Positive Full-Scale Error Drift 2.5V ≤ V

Negative Full-Scale Error 2.5V ≤ V
Negative Full-Scale Error Drift 2.5V ≤ V

Output Noise 5V ≤ VCC ≤ 5.5V, V

≤ VCC, –FS ≤ VIN ≤ +FS (Note 5)

REF

= 5V, V

REF

= 2.5V, V

REF

≤ VCC, GND ≤ IN+ = IN– ≤ VCC (Note 13)

REF

≤ VCC, GND ≤ IN+ = IN– ≤ V

REF

≤ VCC, IN+ = 0.75V

REF

≤ VCC, IN+ = 0.75V

REF

≤ VCC, IN– = 0.75V

REF

≤ VCC, IN– = 0.75V

REF

= 5V, GND ≤ IN– = IN+ ≤ V

REF

= 2.5V (Note 6)

IN(CM)

IN(CM)

, IN– = 0.25V

REF

, IN– = 0.25V

REF

, IN+ = 0.25V

REF

, IN+ = 0.25V

REF

= 1.25V (Note 6) 1

CC

REF

REF

REF

REF

CC

●

24 Bits

●

●

2 10 ppm of V

0.5 2 mV

100 nV/°C

●

25 ppm of V

0.1 ppm of

●

25 ppm of V

0.1 ppm of

0.84 µV

V

REF

V

REF

RMS

U

CO VERTER CHARACTERISTICS

temperature range, otherwise specifications are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Common Mode Rejection DC 2.5V ≤ V
Input Common Mode Rejection 2.5V ≤ V

50Hz ±2%
Input Common Mode Rejection 2.5V ≤ V

60Hz ±2%
Input Normal Mode Rejection 2.5V ≤ V

50Hz ±2%
Input Normal Mode Rejection 2.5V ≤ V

60Hz ±2%
Input Normal Mode Rejection 2.5V ≤ V

50Hz/60Hz ±2%
Reference Common Mode 2.5V ≤ V

Rejection DC

Power Supply Rejection DC V

Power Supply Rejection, 50Hz ± 2% V

Power Supply Rejection, 60Hz ± 2% V

REF

REF

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

≤ VCC, GND ≤ IN– = IN+ ≤ V

REF

= 2.5V, IN– = IN+ = GND 120 dB

= 2.5V, IN– = IN+ = GND (Notes 7, 9) 120 dB

= 2.5V, IN– = IN+ = GND (Notes 8, 9) 120 dB

The ● denotes the specifications which apply over the full operating

= 25°C. (Notes 3, 4)

A

(Note 5)

CC

(Note 5)

CC

(Note 5)

CC

(Notes 5, 7)

CC

(Notes 5, 8)

CC

(Notes 5, 9)

CC

(Note 5)

CC

●

140 dB

●

140 dB

●

140 dB

●

110 120 dB

●

110 120 dB

●

87 dB

●

120 140 dB

REF

REF

/°C

REF

/°C

UUU

A ALOG I PUT AUD REFERE CE

temperature range, otherwise specifications are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

+

IN

–

IN

FS Full Scale of the Differential Input (IN+ – IN–)

LSB Least Significant Bit of the Output Code

V

IN

V

REF

Absolute/Common Mode IN+ Voltage GND – 0.3V VCC + 0.3V V

Absolute/Common Mode IN– Voltage GND – 0.3V VCC + 0.3V V

Input Differential Voltage Range (IN+ – IN–)

Reference Voltage Range (REF+ – REF–)

= 25°C. (Note 3)

A

The ● denotes the specifications which apply over the full operating

●

0.5V

REF

●

●

●

24

FS/2

–FS +FS V

0.1 V

CC

2485fa

3

V

V

LTC2485

UUU

A ALOG I PUT AUD REFERE CE

temperature range, otherwise specifications are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

CS (IN+)IN

CS (IN–)IN

CS (V

)V

REF

I

I

I

(IN+)IN+ DC Leakage Current Sleep Mode, IN+ = GND

DC_LEAK

(IN–)IN– DC Leakage Current Sleep Mode, IN– = GND

DC_LEAK

DC_LEAK (VREF

+

Sampling Capacitance 11 pF

–

Sampling Capacitance 11 pF

Sampling Capacitance 11 pF

REF

)REF+, REF– DC Leakage Current Sleep Mode, V

= 25°C. (Note 3)

A

The ● denotes the specifications which apply over the full operating

REF

= V

CC

●

●

●

–10 1 10 nA

–10 1 10 nA

–100 1 100 nA

UU

I2C DIGITAL I PUTS A D DIGITAL OUTPUTS

the full operating temperature range, otherwise specifications are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IH

V

IL

V

IL(CA1)

V

IH(CA0/F0,CA1)

R

INH

R

INL

R

INF

I

I

V

HYS

V

OL

t

OF

t

SP

I

IN

C

I

C

B

C

CAX

V

IH(EXT,OSC)

V

IL(EXT,OSC)

High Level Input Voltage

Low Level Input Voltage

Low Level Input Voltage for Address Pin

High Level Input Voltage for Address Pins

Resistance from CA0/F0,CA1 to VCC to Set
Chip Address Bit to 1

Resistance from CA1 to GND to Set
Chip Address Bit to 0

Resistance from CA0/F0, CA1 to VCC or
GND to Set Chip Address Bit to Float

Digital Input Current

Hysteresis of Schmitt Trigger Inputs (Note 5) 0.05V

Low Level Output Voltage SDA I = 3mA

Output Fall Time from V

IHMIN

to V

ILMAX

Bus Load CB 10pF to 400pF (Note 14)

Input Spike Suppression

Input Leakage 0.1V

CC

≤ V

IN

Capacitance for Each I/O Pin

Capacitance Load for Each Bus Line

External Capacitive Load on Chip
Address Pins (CA0/F

High Level CA0/F0 External Oscillator 2.7V ≤ V

Low Level CA0/F0 External Oscillator 2.7V ≤ V

,CA1) for Valid Float

0

CC

CC

= 25°C. (Note 3)

A

≤ V

CC

< 5.5V

< 5.5V

The ● denotes the specifications which apply over

●

0.7V

CC

●

●

●

0.95V

CC

●

●

●

●

●

●

●

●

●

●

●

●

●

2MΩ

–10 10 µA

CC

20+0.1C

B

10 pF

V

– 0.5V V

CC

0.3V

CC

0.05V

CC

10 kΩ

10 kΩ

0.4 V

250 ns

50 ns

1 µA

400 pF

10 pF

0.5 V

V

V

V

V

V

WU

POWER REQUIRE E TS

range, otherwise specifications are at TA = 25°C. (Note 3)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

I

CC

Supply Voltage

Supply Current Conversion Mode (Note 11)

The ● denotes the specifications which apply over the full operating temperature

Sleep Mode (Note 11)

●

●

●

2.7 5.5 V

160 250 µA

12 µA

2485fa

4

LTC2485

WU

TI I G CHARACTERISTICS

range, otherwise specifications are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

f

EOSC

t

HEO

t

LEO

t

CONV_1

t

CONV_2

External Oscillator Frequency Range

External Oscillator High Period

External Oscillator Low Period

Conversion Time for 1x Speed Mode 50Hz Mode

Conversion Time for 2x Speed Mode 50Hz Mode

= 25°C. (Note 3)

A

The ● denotes the specifications which apply over the full operating temperature

60Hz Mode
Simultaneous 50Hz/60Hz Mode
External Oscillator (Note 10)

60Hz Mode
Simultaneous 50Hz/60Hz Mode
External Oscillator (Note 10)

●

●

●

●

●

●

●

●

●

●

●

10 4000 kHz

0.125 100 µs

0.125 100 µs

157.2 160.3 163.5 ms

131.0 133.6 136.3 ms

144.1 146.9 149.9 ms
41036/f

EOSC

ms

78.7 80.3 81.9 ms

65.6 66.9 68.2 ms

72.2 73.6 75.1 ms
20556/f

EOSC

ms

UW

I2C TI I G CHARACTERISTICS

temperature range, otherwise specifications are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

f

SCL

t

HD(SDA)

t

LOW

t

HIGH

t

SU(STA)

t

HD(DAT)

t

SU(DAT)

t

r

t

f

t

SU(STO)

SCL Clock Frequency

Hold Time (Repeated) START Condition

LOW Period of the SCL Clock Pin

HIGH Period of the SCL Clock Pin

Set-Up Time for a Repeated START Condition

Data Hold Time

Data Set-Up Time

Rise Time for Both SDA and SCL Signals (Note 14)

Fall Time for Both SDA and SCL Signals (Note 14)

Set-Up Time for STOP Condition

The ● denotes the specifications which apply over the full operating

= 25°C. (Notes 3, 15)

A

●

●

●

●

●

●

●

●

●

●

0 400 kHz

0.6 µs

1.3 µs

0.6 µs

0.6 µs

0 0.9 µs

100 ns

20+0.1C

B

20+0.1C

B

0.6 µs

300 ns

300 ns

Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.

Note 2: All voltage values are with respect to GND.
Note 3: V

= 2.7V to 5.5V unless otherwise specified.

CC

= REF+ – REF–, V

V

REF

V

= IN+ – IN–, V

IN

INCM

= (REF+ + REF–)/2, FS = 0.5V

REFCM

= (IN+ + IN–)/2.

REF

;

Note 4: Use internal conversion clock or external conversion clock source
with f

= 307.2kHz unless otherwise specified.

EOSC

Note 5: Guaranteed by design, not subject to test.
Note 6: Integral nonlinearity is defined as the deviation of a code from a

straight line passing through the actual endpoints of the transfer curve.
The deviation is measured from the center of the quantization band.

Note 7: 50Hz mode (internal oscillator) or f

= 256kHz ±2% (external

EOSC

oscillator).
Note 8: 60Hz mode (internal oscillator) or f

= 307.2kHz ±2% (external

EOSC

oscillator).
Note 9: Simultaneous 50Hz/60Hz mode (internal oscillator) or f

EOSC

280kHz ±2% (external oscillator).
Note 10: The external oscillator is connected to the CA0/F

external oscillator frequency, f

, is expressed in kHz.

EOSC

pin. The

0

Note 11: The converter uses the internal oscillator.
Note 12: The output noise includes the contribution of the internal

calibration operations.

Note 13: Guaranteed by design and test correlation.
Note 14: C
Note 15: All values refer to V

= capacitance of one bus line in pF.

B

and V

IH(MIN)

IL(MAX)

levels.

=

2485fa

5

LTC2485

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Integral Nonlinearity
(V

= 5V, V

CC

3

VCC = 5V

= 5V

V

REF

2

)

1

REF

0

–1

INL (ppm OF V

–2

–3

= 2.5V

V

IN(CM)

–45°C

85°C

–1.5 –0.5 0.5 1.5

INPUT VOLTAGE (V)

Total Unadjusted Error
(V

= 5V, V

CC

12

VCC = 5V

= 5V

V

REF

8

)

4

REF

0

V

IN(CM)

= 2.5V

REF

25°C

REF

= 5V)

= 5V)

25°C

85°C

–45°C

2485 G01

Integral Nonlinearity
(VCC = 5V, V

3

VCC = 5V

= 2.5V

V

REF

2

)

1

REF

0

–1

INL (ppm OF V

–2

2.5–2–2.5 –1 0 1 2

–3

= 1.25V

V

IN(CM)

–0.75 –0.25 0.25 0.75

= 2.5V)

REF

–45°C, 25°C, 90°C

INPUT VOLTAGE (V)

1.25–1.25

2485 G02

Total Unadjusted Error
(VCC = 5V, V

12

VCC = 5V
V

8

V

)

4

REF

0

REF
IN(CM)

= 2.5V

= 1.25V

REF

= 2.5V)

85°C

25°C

–45°C

Integral Nonlinearity
(VCC = 2.7V, V

3

VCC = 2.7V

= 2.5V

V

REF

2

)

1

REF

0

–1

INL (ppm OF V

–2

–3

= 1.25V

V

IN(CM)

–0.75 –0.25 0.25 0.75

INPUT VOLTAGE (V)

Total Unadjusted Error
(VCC = 2.7V, V

12

VCC = 2.7V

= 2.5V

V

REF

8

)

4

REF

0

V

IN(CM)

= 1.25V

= 2.5V)

REF

–45°C, 25°C, 90°C

= 2.5V)

REF

25°C

1.25–1.25

2485 G03

85°C

–45°C

–4

TUE (ppm OF V

–8

–12

–1.5 –0.5 0.5 1.5

INPUT VOLTAGE (V)

2.5–2–2.5 –1 0 1 2

2485 G04

–4

TUE (ppm OF V

–8

–12

–0.75 –0.25 0.25 0.75

INPUT VOLTAGE (V)

Noise Histogram (6.8sps) Long-Term ADC ReadingsNoise Histogram (7.5sps)

14

10,000 CONSECUTIVE
READINGS

12

= 5V

V

CC

= 5V

V

REF

= 0V

V

10

IN

= 25°C

T

A

8

6

4

NUMBER OF READINGS (%)

2

0

–3

–1.8 –0.6

–2.4 1.2

–1.2 0 1.8

OUTPUT READING (µV)

RMS = 0.60µV

AVERAGE = –0.69µV

0.6

2485 G07

14

10,000 CONSECUTIVE
READINGS

12

= 2.7V

V

CC

= 2.5V

V

REF

= 0V

V

10

IN

= 25°C

T

A

8

6

4

NUMBER OF READINGS (%)

2

0

–3

–1.8 –0.6

–2.4 1.2

–1.2 0 1.8

OUTPUT READING (µV)

2485 G05

RMS = 0.59µV

AVERAGE = –0.19µV

0.6

2485 G08

–4

TUE (ppm OF V

–8

1.25–1.25

–12

ADC READING (µV)

–0.75 –0.25 0.25 0.75

INPUT VOLTAGE (V)

5

VCC = 5V, V

= 25°C, RMS NOISE = 0.60µV

T

4

A

3

2

1

0

–1

–2

–3

–4

–5

0

10

= 5V, VIN = 0V, V

REF

20

TIME (HOURS)

IN(CM)

30 40

= 2.5V

50

1.25–1.25

2485 G06

60

2485 G09

2485fa

6

UW

V

IN(CM)

(V)

–1

OFFSET ERROR (ppm OF V

REF

)

0.1

0.2

0.3

24

2485 G15

0

–0.1

01

356

–0.2

–0.3

VCC = 5V
V

REF

= 5V

V

IN

= 0V

T

A

= 25°C

TYPICAL PERFOR A CE CHARACTERISTICS

RMS Noise
vs Input Differential Voltage RMS Noise vs V

1.0
VCC = 5V

= 5V

V

REF

0.9

)

REF

0.8

V

IN(CM)

T

A

= 2.5V

= 25°C

1.0

0.9

0.8

VCC = 5V

= 5V

V

REF

= 0V

V

IN

V

IN(CM)

T

= 25°C

A

= GND

IN(CM)

LTC2485

RMS Noise vs Temperature (TA)

1.0
VCC = 5V

= 5V

V

REF

0.9

= 0V

V

IN

= GND

V

IN(CM)

0.8

0.7

0.6

RMS NOISE (ppm OF V

0.5

0.4
–1.5 –0.5 0.5 1.5

INPUT DIFFERENTIAL VOLTAGE (V)

RMS Noise vs V

1.0

V

= 2.5V

REF

= 0V

V

IN

= GND

V

0.9

IN(CM)

= 25°C

T

A

0.8

0.7

RMS NOISE (µV)

0.6

0.5

0.4

2.7

3.1 3.5

CC

4.3 5.1 5.5

3.9 4.7
VCC (V)

2485 G10

2485 G13

0.7

RMS NOISE (µV)

0.6

0.5

0.4
–1

2.5–2–2.5 –1 0 1 2

01

RMS Noise vs V

1.0

VCC = 5V

= 0V

V

IN

0.9

0.8

0.7

RMS NOISE (µV)

0.6

0.5

0.4

= GND

V

IN(CM)

= 25°C

T

A

0

1234

356

24

V

(V)

IN(CM)

REF

V

(V)

REF

2485 G11

5

2485 G14

0.7

RMS NOISE (µV)

0.6

0.5

0.4
–45

–30 –15 15

Offset Error vs V

0304560

TEMPERATURE (°C)

IN(CM)

75 90

2485 G12

Offset Error vs Temperature Offset Error vs V

0.3
VCC = 5V

V

REF

0.2

V

)

IN

V

REF

IN(CM)

0.1

0

–0.1

OFFSET ERROR (ppm OF V

–0.2

–0.3

–30 0

–45

= 5V

= 0V

= GND

–15

TEMPERATURE (°C)

30 90

15

45

CC

0.3
REF+ = 2.5V

–

= GND

REF

)

REF

OFFSET ERROR (ppm OF V

60

75

2485 G16

0.2

0.1

–0.1

–0.2

–0.3

0

2.7

= 0V

V

IN

V

IN(CM)

= 25°C

T

A

3.1 3.5

= GND

4.3 5.1 5.5

3.9 4.7
VCC (V)

2485 G17

Offset Error vs V

0.3

0.2

)

REF

0.1

0

–0.1

OFFSET ERROR (ppm OF V

–0.2

–0.3

0

1234

REF

VCC = 5V

–

= GND

REF

= 0V

V

IN

= GND

V

IN(CM)

= 25°C

T

A

V

(V)

REF

5

2485.G18

2485fa

7

LTC2485

TEMPERATURE (°C)

–45 –30

300

FREQUENCY (kHz)

304

310

–15

30

45

2485 G21

302

308

306

150

60 75

90

VCC = 4.1V
V

REF

= 2.5V

V

IN

= 0V

V

IN(CM)

= GND

FREQUENCY AT VCC (Hz)

0

–140

REJECTION (dB)

–120

–80

–60

–40

0

20

100

140

2485 G24

–100

–20

80

180

220200

40

60

120 160

VCC = 4.1V DC ±1.4V
V

REF

= 2.5V

IN

+

= GND

IN

–

= GND

T

A

= 25°C

TEMPERATURE (°C)

–45

0

SLEEP MODE CURRENT (µA)

0.2

0.6

0.8

1.0

2.0

1.4

–15

15

30 90

2485 G27

0.4

1.6

1.8

1.2

–30 0

45

60

75

VCC = 5V

VCC = 2.7V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Temperature Sensor
vs Temperature

0.40

VCC = 5V

= 1.4V

V

REF

0.35

(V)

REF

0.30

/V

PTAT

V

0.25

0.20

–60

30090–30 60

TEMPERATURE (°C)

On-Chip Oscillator Frequency
vs V

CC

310

308

306

V

REF

V

IN

V

IN(CM)

= 2.5V

= 0V

2485 G19

= GND

120

Temperature Sensor Error
vs Temperature

5

VCC = 5V

4

3

2

1

0

–1

–2

TEMPERATURE ERROR (°C)

–3

–4

–5

–30

–60

0

TEMPERATURE (°C)

PSRR vs Frequency at V

0

VCC = 4.1V DC

= 2.5V

V

REF

–20

+

= GND

IN

–

= GND

IN

–40

= 25°C

T

A

–60

On-Chip Oscillator Frequency
vs Temperature

V

= 1.4V

REF

30

60

90

120

2485 G20

CC

PSRR vs Frequency at V

CC

FREQUENCY (kHz)

REJECTION (dB)

8

304

302

300

2.5

3.5 4.0 4.5

3.0
VCC (V)

PSRR vs Frequency at V

0

VCC = 4.1V DC ±0.7V

= 2.5V

V

REF

–20

+

= GND

IN

–

= GND

IN

–40

= 25°C

T

A

–60

–80

–100

–120

–140

30600

30650 30700 30800

FREQUENCY AT VCC (Hz)

CC

30750

5.0 5.5

2485 G22

2485 G25

–80

REJECTION (dB)

–100

–120

–140

1

10 100

FREQUENCY AT VCC (Hz)

Conversion Current
vs Temperature

200

180

160

140

CONVERSION CURRENT (µA)

120

100

–30 0

–45

–15

10k 1M

1k 100k

VCC = 5V

VCC = 2.7V

30 90

45

15

TEMPERATURE (°C)

2485 G23

Sleep Mode Current
vs Temperature

60

75

2485 G26

2485fa

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC2485

Conversion Current
vs Output Data Rate

500

V

= V

REF

CC

IN+ = GND

450

–

= GND

IN

= EXT OSC

CA0/F

400

350

300

250

SUPPLY CURRENT (µA)

200

150

100

0

= 25°C

T

A

0

20 40 60 1007010 30 50 90

OUTPUT DATA RATE (READINGS/SEC)

VCC = 5V

Integral Nonlinearity (2x Speed
Mode; V

3

VCC = 2.7V
V

REF

2

V

IN(CM)

)

1

REF

0

–1

INL (ppm OF V

–2

–3

= 2.7V, V

CC

= 2.5V

= 1.25V

90°C

–45°C, 25°C

–0.75 –0.25 0.25 0.75

INPUT VOLTAGE (V)

REF

VCC = 3V

80

= 2.5V)

2485 G28

2485 G31

Integral Nonlinearity (2x Speed
Mode; V

3

2

)

1

REF

0

–1

INL (ppm OF V

–2

–3

= 5V, V

CC

–1.5 –0.5 0.5 1.5

INPUT VOLTAGE (V)

= 5V)

REF

VCC = 5V
V
V

25°C, 90°C

REF
IN(CM)

–45°C

= 5V

= 2.5V

2.5–2–2.5 –1 0 1 2

2485 G29

Noise Histogram
(2x Speed Mode)

16

10,000 CONSECUTIVE
READINGS

14

= 5V

V

CC

= 5V

V

REF

12

= 0V

V

IN

= 25°C

T

A

10

8

6

4

NUMBER OF READINGS (%)

2

1.25–1.25

0

179

181.4 183.8 188.6
OUTPUT READING (µV)

RMS = 0.86µV

AVERAGE = 0.184mV

186.2

2485 G32

Integral Nonlinearity (2x Speed
Mode; VCC = 5V, V

3

VCC = 5V

= 2.5V

V

REF

2

)

1

REF

0

–1

INL (ppm OF V

–2

–3

= 1.25V

V

IN(CM)

–45°C, 25°C

–0.75 –0.25 0.25 0.75

RMS Noise vs V

90°C

INPUT VOLTAGE (V)

REF

REF

= 2.5V)

(2x Speed Mode)

1.0

0.8

0.6

0.4

RMS NOISE (µV)

VCC = 5V

0.2
= 0V

V

IN

= GND

V

IN(CM)

= 25°C

T

A

0

1

0

3

2

V

(V)

REF

1.25–1.25

2485 G30

4

5

2485 G33

Offset Error vs V
(2x Speed Mode)

200

VCC = 5V

198

196

194

192

190

188

186

OFFSET ERROR (µV)

184

182

180

= 5V

V

REF

= 0V

V

IN

= 25°C

T

A

–1

0

IN(CM)

Offset Error vs Temperature
(2x Speed Mode)

240

VCC = 5V

= 5V

V

REF

230

= 0V

V

IN

= GND

V

IN(CM)

220

210

200

190

OFFSET ERROR (µV)

180

170

1

V

IN(CM)

4

(V)

3

2

5

6

2485 G34

160

–30 90

–45

–15

15

30

0

TEMPERATURE (°C)

75

45

60

2485 G35

2485fa

9

LTC2485

FREQUENCY AT VCC (Hz)

1

0

–20

–40

–60

–80

–100

–120

–140

1k 100k

2485 G38

10 100

10k 1M

REJECTION (dB)

VCC = 4.1V DC
REF

+

= 2.5V

REF

–

= GND

IN

+

= GND

IN

–

= GND

T

A

= 25°C

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Offset Error vs V
(2x Speed Mode)

250

V

= 2.5V

REF

= 0V

V

IN

V

IN(CM)

200

= 25°C

T

A

150

100

OFFSET ERROR (µV)

50

0

3

2.7

= GND

3.5

–20

–40

–60

–80

RREJECTION (dB)

–100

–120

–140

CC

4

VCC (V)

4.5

5.5

5

2485 G36

PSRR vs Frequency at V
(2x Speed Mode)

0

VCC = 4.1V DC ±1.4V

+

= 2.5V

REF

–

= GND

REF

+

= GND

IN

–

= GND

IN

= 25°C

T

A

0

60

20

80

40

FREQUENCY AT VCC (Hz)

100

120 160

140

Offset Error vs V
(2x Speed Mode)

240

VCC = 5V

= 0V

V

IN

230

V

IN(CM)

= 25°C

T

A

220

210

200

190

OFFSET ERROR (µV)

180

170

160

0

CC

180

2485 G39

REF

= GND

12 4

220200

3

V

(V)

REF

–20

–40

–60

–80

REJECTION (dB)

–100

–120

–140

30600

PSRR vs Frequency at V
(2x Speed Mode)

5

2485 G37

PSRR vs Frequency at V
(2x Speed Mode)

0

VCC = 4.1V DC ±0.7V

+

= 2.5V

REF

–

= GND

REF

+

= GND

IN

–

= GND

IN

= 25°C

T

A

30650 30700 30800

FREQUENCY AT VCC (Hz)

CC

CC

30750

2485 G40

10

2485fa

LTC2485

U

UU

PI FU CTIO S

REF+ (Pin 1), REF– (Pin 3): Differential Reference Input.
The voltage on these pins can have any value between GND
and V
more positive than the reference negative input, REF
at least 0.1V.

V

(Pin 8) with a 1µF tantalum capacitor in parallel with 0.1µF
ceramic capacitor as close to the part as possible.

IN+ (Pin 4), IN– (Pin 5): Differential Analog Input. The
voltage on these pins can have any value between
GND – 0.3V and V
converter bipolar input range (VIN = IN+ – IN–) extends
from –0.5 • V
the converter produces unique overrange and underrange
output codes.

SCL (Pin 6): Serial Clock Pin of the I2C Interface. The
LTC2485 can only act as a slave and the SCL pin only
accepts external serial clock. Data is shifted into the SDA
pin on the rising edges of the SCL clock and output
through the SDA pin on the falling edges of the
SCL clock.

as long as the reference positive input, REF+, is

CC

(Pin 2): Positive Supply Voltage. Bypass to GND

CC

+ 0.3V. Within these limits the

CC

to 0.5 • V

REF

. Outside this input range

REF

–

, by

2

SDA (Pin 7): Bidirectional Serial Data Line of the I

C
Interface. In the transmitter mode (Read), the conversion
result is output through the SDA pin, while in the receiver
mode (Write), the device configuration bits are input
through the SDA pin. At data input mode, the pin is high
impedance; while at data output mode, it is an open-drain
N-channel driver and therefore an external pull-up resistor
or current source to V

is needed.

CC

GND (Pin 8): Ground. Connect this pin to a ground plane
through a low impedance connection.

CA1 (Pin 9): Chip Address Control Pin. The CA1 pin is
configured as a three state (LOW, HIGH, or Floating)
address control bit for the device I

CA0/F

(Pin 10): Chip Address Control Pin/External Clock

0

Input Pin. When no transition is detected on the CA0/F

2

C address.

0

pin, it is a two state (HIGH or Floating) address control bit
for the device I
external clock signal with a frequency f

2

C address. When the pin is driven by an

of at least

EOSC

10kHz, the converter uses this signal as its system clock
and the fundamental digital filter rejection null is located at
a frequency f

/5120 and sets the Chip Address CA0

EOSC

internally to a HIGH.

UU

W

FU CTIO AL BLOCK DIAGRA

+

REF

1

+

IN

4

–

IN

5

TEMP

SENSOR

MUX

+

IN

–

IN

REF

AUTOCALIBRATION

–

REF

3

+

REF

3RD ORDER

∆Σ ADC

–

AND CONTROL

2

V

CC

SCL

6

SDA

CA1

CA0/F

0

2485 FB

7

9

10

2485fa

8

GND

I2C

SERIAL

INTERFACE

INTERNAL

OSCILLATOR

11

LTC2485

WUUU

APPLICATIO S I FOR ATIO

CONVERTER OPERATION

Converter Operation Cycle

The LTC2485 is a low power, ∆Σ analog-to-digital con-

2

verter with an I

C interface. After power on reset, its
operation is made up of three states. The converter
operating cycle begins with the conversion, followed by
the low power sleep state and ends with the data output/
input (see Figure 1).

POWER ON RESET

DEFAULT CONFIGURATION:

EXTERNAL INPUT

50/60Hz REJECTION

1X SPEED, AUTOCAL

CONVERSION

SLEEP

NO

ACKNOWLEDGE

YES

DATA OUTPUT

LTC2485 is addressed for a read operation, the device
begins outputting the conversion result under control of
the serial clock (SCL). There is no latency in the conver­sion result. The data output is 32 bits long and contains a
24-bit plus sign conversion result. This result is shifted
out on the SDA pin under the control of the SCL. Data is
updated on the falling edges of SCL allowing the user to
reliably latch data on the rising edge of SCL. In write
operation, the device accepts one configuration byte and
the data is shifted in on the rising edges of the SCL. A new
conversion is initiated by a STOP condition following a
valid write operation or at the conclusion of a data read
operation (read out all 32 bits).

2

I

C INTERFACE

2

The LTC2485 communicates through an I

2

The I

C interface is a 2-wire open-drain interface sup-

C interface.

porting multiple devices and masters on a single bus. The
connected devices can only pull the bus wires LOW and
they never drive the bus HIGH. The bus wires are exter­nally connected to a positive supply voltage via a current­source or pull-up resistor. When the bus is free, both
lines are HIGH. Data on the I2C-bus can be transferred at
rates of up to 100kbit/s in the Standard-mode and up to
400kbit/s in the Fast-mode.

STOP

NO

OR READ

32-BITS

YES

2485 F01

Figure 1. LTC2485 State Transition Diagram

Initially, the LTC2485 performs a conversion. Once the
conversion is complete, the device enters the sleep state.
While in this sleep state, power consumption is reduced
by two orders of magnitude. The part remains in the sleep
state as long as it is not addressed for a read/write
operation. The conversion result is held indefinitely in a
static shift register while the converter is in the sleep state.

The device will not acknowledge an external request
during the conversion state. After a conversion is finished,
the device is ready to accept a read/write request. Once the

Each device on the I2C bus is recognized by a unique
address stored in that device and can operate as either a
transmitter or receiver, depending on the function of the
device. In addition to transmitters and receivers, devices
can also be considered as masters or slaves when per­forming data transfers. A master is the device which
initiates a data transfer on the bus and generates the clock
signals to permit that transfer. At the same time any device
addressed is considered a slave.

The LTC2485 can only be addressed as a slave. Once
addressed, it can receive configuration bits or transmit the
last conversion result. Therefore the serial clock line SCL
is an input only and the data line SDA is bidirectional. The
device supports the Standard-mode and the Fast-mode
for data transfer speeds up to 400kbit/s. Figure 2 shows
the definition of timing for Fast/Standard-mode devices

2

on the I

C-bus.

2485fa

12