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LTC2485
24-Bit ∆Σ ADC with Easy Drive
Input Current Cancellation and I2C Interface
FEATURES
Easy Drive Technology Enables Rail-to-Rail Inputs
with Zero Differential Input Current
Directly Digitizes High Impedance Sensors with
Full Accuracy
www.DataSheetI4nUt.ecogmrated 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
DESCRIPTIO
The LTC®2485 combines a 24-bit plus sign No Latency∆ΣTM
analog-to-digital converter with patented Easy DriveTM tech-
nology and I2C digital interface. The patented sampling
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-to-
rail 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 I2C
interface to measure an external signal or internal tem-
perature 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 VCC. The LTC2485 includes an on-chip trimmed oscil-
lator eliminating the need for external crystals or oscilla-
tors. Absolute accuracy and low drift are automatically
maintained through continuous, transparent, offset and
full-scale calibration.
TYPICAL APPLICATIO
VCC
1µF
10k
SENSE
10k
IDIFF = 0
1µF
REF+
VIN+
VCC
LTC2485
VIN–
GND
REF
SCL 2-WIRE
SDA I2C INTERFACE
CA0/F0
CA1
2485 TA01
6 ADDRESSES
+FS Error vs RSOURCE at IN+ and IN
80
VCC = 5V
60
40
VVVRIINNE+–F
=
=
=
5V
3.75V
1.25V
FO = GND
20 TA = 25°C
0
CIN = 1µF
–20
–40
–60
–80
1
10 100 1k 10k 100k
RSOURCE ()
2485 TA02
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LTC2485
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 (VCC + 0.3V)
Reference Input Voltage to GND .. – 0.3V to (VCC + 0.3V)
Digital Input Voltage to GND ........ – 0.3V to (VCC + 0.3V)
Digital Output Voltage to GND ..... – 0.3V to (VCC + 0.3V)
Operating Temperature Range
LTC2485C ................................................... 0°C to 70°C
LTC2485I ................................................ – 40°C to 85°C
w w w . D a t aSSthoeraegt 4eUT.ecmo mperature Range ................ – 65°C to 125°C
UW U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
REF+ 1
VCC
REF
IN+
IN
2
3
4
5
10 CA0/F0
9 CA1
11 8 GND
7 SDA
6 SCL
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/ W
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC2485CDD
LTC2485IDD
DD PART MARKING*
LBST
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.
UW
ELECTRICAL CHARACTERISTICS ( OR AL SPEED) The denotes the specifications which
apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Notes 3, 4)
PARAMETER
CONDITIONS
MIN TYP MAX
UNITS
Resolution (No Missing Codes)
0.1 VREF VCC, –FS VIN +FS (Note 5)
24
Bits
Integral Nonlinearity
Offset Error
5V VCC 5.5V, VREF = 5V, VIN(CM) = 2.5V (Note 6)
2.7V VCC 5.5V, VREF = 2.5V, VIN(CM) = 1.25V (Note 6)
2.5V VREF VCC, GND IN+ = INVCC (Note 13)
2 10 ppm of VREF
1 ppm of VREF
0.5 2.5
µV
Offset Error Drift
Positive Full-Scale Error
Positive Full-Scale Error Drift
Negative Full-Scale Error
Negative Full-Scale Error Drift
2.5V VREF VCC, GND IN+ = INVCC
2.5V VREF VCC, IN+ = 0.75VREF, IN= 0.25VREF
2.5V VREF VCC, IN+ = 0.75VREF, IN= 0.25VREF
2.5V VREF VCC, IN= 0.75VREF, IN+ = 0.25VREF
2.5V VREF VCC, IN= 0.75VREF, IN+ = 0.25VREF
10 nV/°C
25 ppm of VREF
0.1 ppm of
VREF/°C
25 ppm of VREF
0.1 ppm of
VREF/°C
Total Unadjusted Error
Output Noise
5V VCC 5.5V, VREF = 2.5V, VIN(CM) = 1.25V (Note 6)
5V VCC 5.5V, VREF = 5V, VIN(CM) = 2.5V (Note 6)
2.7V VCC 5.5V, VREF = 2.5V, VIN(CM) = 1.25V (Note 6)
5V VCC 5.5V, VREF = 5V, GND IN= IN+ VCC (Note 12)
15 ppm of VREF
15 ppm of VREF
15 ppm of VREF
0.6 µVRMS
Internal PTAT Signal
TA = 27°C
420 mV
Internal PTAT Temperature Coefficient
1.4 mV/°C
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LTC2485
ELECTRICAL CHARACTERISTICS (2x SPEED) The denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at TA = 25°C. (Notes 3, 4)
PARAMETER
Resolution (No Missing Codes)
Integral Nonlinearity
Offset Error
Offset Error Drift
Positive Full-Scale Error
Positive Full-Scale Error Drift
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Negative Full-Scale Error
Negative Full-Scale Error Drift
Output Noise
CONDITIONS
0.1 VREF VCC, –FS VIN +FS (Note 5)
5V VCC 5.5V, VREF = 5V, VIN(CM) = 2.5V (Note 6)
2.7V VCC 5.5V, VREF = 2.5V, VIN(CM) = 1.25V (Note 6)
2.5V VREF VCC, GND IN+ = INVCC (Note 13)
2.5V VREF VCC, GND IN+ = INVCC
2.5V VREF VCC, IN+ = 0.75VREF, IN= 0.25VREF
2.5V VREF VCC, IN+ = 0.75VREF, IN= 0.25VREF
2.5V VREF VCC, IN= 0.75VREF, IN+ = 0.25VREF
2.5V VREF VCC, IN= 0.75VREF, IN+ = 0.25VREF
5V VCC 5.5V, VREF = 5V, GND IN= IN+ VCC
MIN TYP MAX
UNITS
24
Bits
2 10 ppm of VREF
1
0.5 2
mV
100 nV/°C
25 ppm of VREF
0.1 ppm of
VREF/°C
25 ppm of VREF
0.1 ppm of
VREF/°C
0.84 µVRMS
CO VERTER CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Notes 3, 4)
PARAMETER
Input Common Mode Rejection DC
Input Common Mode Rejection
50Hz ±2%
Input Common Mode Rejection
60Hz ±2%
Input Normal Mode Rejection
50Hz ±2%
Input Normal Mode Rejection
60Hz ±2%
Input Normal Mode Rejection
50Hz/60Hz ±2%
Reference Common Mode
Rejection DC
Power Supply Rejection DC
Power Supply Rejection, 50Hz ±2%
Power Supply Rejection, 60Hz ±2%
CONDITIONS
2.5V VREF VCC, GND IN= IN+ VCC (Note 5)
2.5V VREF VCC, GND IN= IN+ VCC (Note 5)
2.5V VREF VCC, GND IN= IN+ VCC (Note 5)
2.5V VREF VCC, GND IN= IN+ VCC (Notes 5, 7)
2.5V VREF VCC, GND IN= IN+ VCC (Notes 5, 8)
2.5V VREF VCC, GND IN= IN+ VCC (Notes 5, 9)
2.5V VREF VCC, GND IN= IN+ VCC (Note 5)
VREF = 2.5V, IN= IN+ = GND
VREF = 2.5V, IN= IN+ = GND (Notes 7, 9)
VREF = 2.5V, IN= IN+ = GND (Notes 8, 9)
MIN TYP MAX
140
140
140
110 120
110 120
87
120 140
120
120
120
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
U UU
U
A ALOG I PUT A D REFERE CE The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
IN+
IN
FS
LSB
VIN
VREF
PARAMETER
Absolute/Common Mode IN+ Voltage
Absolute/Common Mode INVoltage
Full Scale of the Differential Input (IN+ – IN)
Least Significant Bit of the Output Code
Input Differential Voltage Range (IN+ – IN)
Reference Voltage Range (REF+ – REF)
CONDITIONS
MIN
GND – 0.3V
GND – 0.3V
0.5VREF
FS/224
–FS
0.1
TYP MAX UNITS
VCC + 0.3V
VCC + 0.3V
V
V
V
+FS V
VCC V
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LTC2485
U UU
U
A ALOG I PUT A D REFERE CE The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
CS (IN+)
CS (IN)
CS (VREF)
IDC_LEAK (IN+)
IDC_LEAK (IN)
IDC_LEAK (VREF)
PARAMETER
IN+ Sampling Capacitance
INSampling Capacitance
VREF Sampling Capacitance
IN+ DC Leakage Current
INDC Leakage Current
REF+, REFDC Leakage Current
CONDITIONS
Sleep Mode, IN+ = GND
Sleep Mode, IN= GND
Sleep Mode, VREF = VCC
MIN
–10
–10
–100
TYP MAX UNITS
11 pF
11 pF
11 pF
1 10
nA
1 10
nA
1 100
nA
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I2C DIGITAL I PUTS A D DIGITAL OUTPUTS The denotes the specifications which apply over
the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
VIH
VIL
VIL(CA1)
VIH(CA0/F0,CA1)
RINH
RINL
RINF
II
VHYS
VOL
tOF
tSP
IIN
CI
CB
CCAX
VIH(EXT,OSC)
VIL(EXT,OSC)
PARAMETER
CONDITIONS
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)
Low Level Output Voltage SDA
I = 3mA
Output Fall Time from VIHMIN to VILMAX
Input Spike Suppression
Bus Load CB 10pF to 400pF (Note 14)
Input Leakage
Capacitance for Each I/O Pin
0.1VCC VIN VCC
Capacitance Load for Each Bus Line
External Capacitive Load on Chip
Address Pins (CA0/F0,CA1) for Valid Float
High Level CA0/F0 External Oscillator
Low Level CA0/F0 External Oscillator
2.7V VCC < 5.5V
2.7V VCC < 5.5V
MIN
0.7VCC
0.95VCC
2
–10
0.05VCC
20+0.1CB
10
VCC – 0.5V
TYP MAX UNITS
V
0.3VCC
0.05VCC
V
V
V
10 k
10 k
M
10 µA
V
0.4 V
250 ns
50 ns
1 µA
pF
400 pF
10 pF
V
0.5 V
POWER REQUIRE E TS The denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
VCC
ICC
PARAMETER
Supply Voltage
Supply Current
CONDITIONS
Conversion Mode (Note 11)
Sleep Mode (Note 11)
MIN
2.7
TYP MAX UNITS
5.5 V
160 250
12
µA
µA
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LTC2485
TI I G CHARACTERISTICS The denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
fEOSC
tHEO
tLEO
tCONV_1
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time for 1x Speed Mode
www.DataShteCeOtN4VU_2.com Conversion Time for 2x Speed Mode
50Hz Mode
60Hz Mode
Simultaneous 50Hz/60Hz Mode
External Oscillator (Note 10)
50Hz Mode
60Hz Mode
Simultaneous 50Hz/60Hz Mode
External Oscillator (Note 10)
10
0.125
0.125
157.2
131.0
144.1
78.7
65.6
72.2
4000
100
100
160.3
133.6
146.9
41036/fEOSC
80.3
66.9
73.6
20556/fEOSC
163.5
136.3
149.9
81.9
68.2
75.1
kHz
µs
µs
ms
ms
ms
ms
ms
ms
ms
ms
I2C
WU
TI I G
CHARACTERISTICS
The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Notes 3, 15)
SYMBOL
fSCL
tHD(SDA)
tLOW
tHIGH
tSU(STA)
tHD(DAT)
tSU(DAT)
tr
tf
tSU(STO)
PARAMETER
CONDITIONS
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
MIN TYP MAX UNITS
0
400 kHz
0.6
µs
1.3
µs
0.6
µs
0.6
µs
0
0.9 µs
100
ns
20+0.1CB
20+0.1CB
0.6
300 ns
300 ns
µs
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: All voltage values are with respect to GND.
Note 3: VCC = 2.7V to 5.5V unless otherwise specified.
VREF = REF+ – REF, VREFCM = (REF+ + REF)/2, FS = 0.5VREF;
VIN = IN+ – IN, VINCM = (IN+ + IN)/2.
Note 4: Use internal conversion clock or external conversion clock source
with fEOSC = 307.2kHz unless otherwise specified.
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 fEOSC = 256kHz ±2% (external
oscillator).
Note 8: 60Hz mode (internal oscillator) or fEOSC = 307.2kHz ±2% (external
oscillator).
Note 9: Simultaneous 50Hz/60Hz mode (internal oscillator) or fEOSC =
280kHz ±2% (external oscillator).
Note 10: The external oscillator is connected to the CA0/F0 pin. The
external oscillator frequency, fEOSC, is expressed in kHz.
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: CB = capacitance of one bus line in pF.
Note 15: All values refer to VIH(MIN) and VIL(MAX) levels.
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