LTC2485
24-Bit
∆Σ
ADC with Easy Drive
Input Current Cancellation and I
2
C Interface
FEATURES
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DESCRIPTIO
Easy Drive
TM
Technology Enables Rail-to-Rail
Inputs with Zero Differential Input Current
Directly Digitizes High Impedance Sensors with
Full Accuracy
Integrated Temperature Sensor
GND to V
CC
Input/Reference Common Mode Range
2-Wire I
2
C 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
The LTC
®
2485 combines a 24-bit plus sign No Latency
∆Σ
TM
analog-to-digital converter with patented Easy Drive tech-
nology and I
2
C 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 I
2
C
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 V
CC
) independent of the reference voltage. The
reference can be as low as 100mV or can be tied directly
to V
CC
. 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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No Latency
∆Σ
and Easy Drive are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
APPLICATIO S
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Direct Sensor Digitizer
Weight Scales
Direct Temperature Measurement
Strain Gauge Transducers
Instrumentation
Industrial Process Control
DVMs and Meters
TYPICAL APPLICATIO
V
CC
+FS Error vs R
SOURCE
at IN
+
and IN
–
V
CC
= 5V
V
REF
= 5V
60
V
IN+
= 3.75V
–
40 V
IN
= 1.25V
F
O
= GND
20 T
A
= 25°C
C
IN
= 1µF
0
–20
–40
80
10k
SENSE
10k
I
DIFF
= 0
1µF
V
IN+
V
IN–
REF
+
LTC2485
GND
V
CC
SCL
SDA
CA0/F
0
CA1
2485 TA01
2-WIRE
I
2
C INTERFACE
6 ADDRESSES
+FS ERROR (ppm)
1µF
REF
–
–60
–80
1
10
100
1k
R
SOURCE
(Ω)
10k
100k
2485 TA02
U
2485fa
U
U
1
LTC2485
ABSOLUTE
(Notes 1, 2)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
REF
+
1
V
CC
2
REF
–
IN
–
Supply Voltage (V
CC
) to GND ...................... – 0.3V to 6V
Analog Input Voltage to GND ....... – 0.3V to (V
CC
+ 0.3V)
Reference Input Voltage to GND .. – 0.3V to (V
CC
+ 0.3V)
Digital Input Voltage to GND ........ – 0.3V to (V
CC
+ 0.3V)
Digital Output Voltage to GND ..... – 0.3V to (V
CC
+ 0.3V)
Operating Temperature Range
LTC2485C ................................................... 0°C to 70°C
LTC2485I ................................................ – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 125°C
10 CA0/F
0
9 CA1
11
8 GND
7 SDA
6 SCL
3
5
IN
+
4
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 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.
ELECTRICAL CHARACTERISTICS ( OR AL SPEED)
PARAMETER
Resolution (No Missing Codes)
Integral Nonlinearity
Offset Error
Offset Error Drift
Positive Full-Scale Error
Positive Full-Scale Error Drift
Negative Full-Scale Error
Negative Full-Scale Error Drift
Total Unadjusted Error
CONDITIONS
0.1
≤
V
REF
≤
V
CC
, –FS
≤
V
IN
≤
+FS (Note 5)
5V
≤
V
CC
≤
5.5V, V
REF
= 5V, V
IN(CM)
= 2.5V (Note 6)
2.7V
≤
V
CC
≤
5.5V, V
REF
= 2.5V, V
IN(CM)
= 1.25V (Note 6)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
+
= IN
–
≤
V
CC
(Note 13)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
+
= IN
–
≤
V
CC
2.5V
≤
V
REF
≤
V
CC
, IN
+
= 0.75V
REF
, IN
–
= 0.25V
REF
2.5V
≤
V
REF
≤
V
CC
, IN
+
= 0.75V
REF
, IN
–
= 0.25V
REF
2.5V
≤
V
REF
≤
V
CC
, IN
–
= 0.75V
REF
, IN
+
= 0.25V
REF
2.5V
≤
V
REF
≤
V
CC
, IN
–
= 0.75V
REF
, IN
+
= 0.25V
REF
5V
≤
V
CC
≤
5.5V, V
REF
= 2.5V, V
IN(CM)
= 1.25V (Note 6)
5V
≤
V
CC
≤
5.5V, V
REF
= 5V, V
IN(CM)
= 2.5V (Note 6)
2.7V
≤
V
CC
≤
5.5V, V
REF
= 2.5V, V
IN(CM)
= 1.25V (Note 6)
The
●
denotes the specifications which
apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3, 4)
MIN
●
●
●
●
TYP
2
1
0.5
10
MAX
10
2.5
25
24
ppm of V
REF
ppm of V
REF
µV
nV/°C
ppm of V
REF
ppm of
V
REF
/°C
0.1
●
25
0.1
15
15
15
0.6
420
1.4
ppm of V
REF
ppm of
V
REF
/°C
ppm of V
REF
ppm of V
REF
ppm of V
REF
µV
RMS
mV
mV/°C
Output Noise
Internal PTAT Signal
Internal PTAT Temperature Coefficient
5V
≤
V
CC
≤
5.5V, V
REF
= 5V, GND
≤
IN
–
= IN
+
≤
V
CC
(Note 12)
T
A
= 27°C
2
U
UNITS
Bits
2485fa
W
U
W
U
U
W W
W
LTC2485
ELECTRICAL CHARACTERISTICS (2x SPEED)
PARAMETER
Resolution (No Missing Codes)
Integral Nonlinearity
Offset Error
Offset Error Drift
Positive Full-Scale Error
Positive Full-Scale Error Drift
Negative Full-Scale Error
Negative Full-Scale Error Drift
Output Noise
CONDITIONS
0.1
≤
V
REF
≤
V
CC
, –FS
≤
V
IN
≤
+FS (Note 5)
The
●
denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3, 4)
MIN
●
●
●
●
TYP
2
1
0.5
100
MAX
10
2
25
UNITS
Bits
ppm of V
REF
mV
nV/°C
ppm of V
REF
ppm of
V
REF
/°C
24
5V
≤
V
CC
≤
5.5V, V
REF
= 5V, V
IN(CM)
= 2.5V (Note 6)
2.7V
≤
V
CC
≤
5.5V, V
REF
= 2.5V, V
IN(CM)
= 1.25V (Note 6)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
+
= IN
–
≤
V
CC
(Note 13)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
+
= IN
–
≤
V
CC
2.5V
≤
V
REF
≤
V
CC
, IN
+
= 0.75V
REF
, IN
–
= 0.25V
REF
2.5V
≤
V
REF
≤
V
CC
, IN
+
= 0.75V
REF
, IN
–
= 0.25V
REF
2.5V
≤
V
REF
≤
V
CC
, IN
–
= 0.75V
REF
, IN
+
= 0.25V
REF
2.5V
≤
V
REF
≤
V
CC
, IN
–
= 0.75V
REF
, IN
+
= 0.25V
REF
5V
≤
V
CC
≤
5.5V, V
REF
= 5V, GND
≤
IN
–
= IN
+
≤
V
CC
0.1
●
25
0.1
0.84
ppm of V
REF
ppm of
V
REF
/°C
µV
RMS
CO VERTER CHARACTERISTICS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 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
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Note 5)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Note 5)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Note 5)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Notes 5, 7)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Notes 5, 8)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Notes 5, 9)
2.5V
≤
V
REF
≤
V
CC
, GND
≤
IN
–
= IN
+
≤
V
CC
(Note 5)
V
REF
= 2.5V, IN
–
= IN
+
= GND
V
REF
= 2.5V, IN
–
= IN
+
= GND (Notes 7, 9)
V
REF
= 2.5V, IN
–
= IN
+
= GND (Notes 8, 9)
●
●
●
●
●
●
●
A ALOG I PUT A D REFERE CE
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
IN
+
IN
–
FS
LSB
V
IN
V
REF
PARAMETER
Absolute/Common Mode IN
+
Voltage
Absolute/Common Mode IN
–
Voltage
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
–
)
●
●
●
●
U
U
U
U
MIN
140
140
140
110
110
87
120
TYP
MAX
UNITS
dB
dB
dB
120
120
dB
dB
dB
140
120
120
120
dB
dB
dB
dB
U
CONDITIONS
MIN
GND – 0.3V
GND – 0.3V
0.5V
REF
FS/2
24
–FS
0.1
TYP
MAX
V
CC
+ 0.3V
V
CC
+ 0.3V
UNITS
V
V
V
+FS
V
CC
V
V
2485fa
3
LTC2485
A ALOG I PUT A D REFERE CE
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
C
S
(IN
+
)
C
S
(IN
–
)
C
S
(V
REF
)
I
DC_LEAK
(IN
+
)
I
DC_LEAK
(IN
–
)
I
DC_LEAK
(V
REF
)
PARAMETER
IN
+
Sampling Capacitance
IN
–
Sampling Capacitance
V
REF
Sampling Capacitance
IN
+
DC Leakage Current
IN
–
DC Leakage Current
REF
+
, REF
–
DC Leakage Current
Sleep Mode, IN
+
= GND
Sleep Mode, IN
–
= GND
Sleep Mode, V
REF
= V
CC
●
●
●
I
2
C DIGITAL I PUTS A D DIGITAL OUTPUTS
SYMBOL
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)
PARAMETER
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/F
0
,CA1 to V
CC
to Set
Chip Address Bit to 1
Resistance from CA1 to GND to Set
Chip Address Bit to 0
Resistance from CA0/F
0
, CA1 to V
CC
or
GND to Set Chip Address Bit to Float
Digital Input Current
Hysteresis of Schmitt Trigger Inputs
Low Level Output Voltage SDA
Output Fall Time from V
IHMIN
to V
ILMAX
Input Spike Suppression
Input Leakage
Capacitance for Each I/O Pin
Capacitance Load for Each Bus Line
External Capacitive Load on Chip
Address Pins (CA0/F
0
,CA1) for Valid Float
High Level CA0/F
0
External Oscillator
Low Level CA0/F
0
External Oscillator
2.7V
≤
V
CC
< 5.5V
2.7V
≤
V
CC
< 5.5V
0.1V
CC
≤
V
IN
≤
V
CC
(Note 5)
I = 3mA
CONDITIONS
The
●
denotes the specifications which apply over
the full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
MIN
●
●
●
●
●
●
●
●
●
Bus Load C
B
10pF to 400pF (Note 14)
●
●
●
●
●
●
●
●
POWER REQUIRE E TS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
The
●
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
●
Conversion Mode (Note 11)
Sleep Mode (Note 11)
4
U
U
U W
U
U
U
U
CONDITIONS
MIN
TYP
11
11
11
MAX
UNITS
pF
pF
pF
–10
–10
–100
1
1
1
10
10
100
nA
nA
nA
TYP
MAX
0.3V
CC
0.05V
CC
UNITS
V
V
V
V
kΩ
kΩ
MΩ
0.7V
CC
0.95V
CC
10
10
2
–10
0.05V
CC
0.4
20+0.1C
B
250
50
1
10
400
10
V
CC
– 0.5V
0.5
10
µA
V
V
ns
ns
µA
pF
pF
pF
V
V
MIN
2.7
●
●
TYP
160
1
MAX
5.5
250
2
UNITS
V
µA
µA
2485fa
LTC2485
TI I G CHARACTERISTICS
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV_1
PARAMETER
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time for 1x Speed Mode
The
●
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
●
●
●
t
CONV_2
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3, 15)
SYMBOL
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)
PARAMETER
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
Fall Time for Both SDA and SCL Signals
Set-Up Time for STOP Condition
(Note 14)
(Note 14)
CONDITIONS
●
●
●
●
●
●
●
●
●
●
I
2
C TI I G CHARACTERISTICS
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
CC
= 2.7V to 5.5V unless otherwise specified.
V
REF
= REF
+
– REF
–
, V
REFCM
= (REF
+
+ REF
–
)/2, FS = 0.5V
REF
;
V
IN
= IN
+
– IN
–
, V
INCM
= (IN
+
+ IN
–
)/2.
Note 4:
Use internal conversion clock or external conversion clock source
with f
EOSC
= 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.
UW
UW
MIN
10
0.125
0.125
157.2
131.0
144.1
78.7
65.6
72.2
TYP
MAX
4000
100
100
UNITS
kHz
µs
µs
ms
ms
ms
ms
ms
ms
ms
ms
50Hz Mode
60Hz Mode
Simultaneous 50Hz/60Hz Mode
External Oscillator (Note 10)
50Hz Mode
60Hz Mode
Simultaneous 50Hz/60Hz Mode
External Oscillator (Note 10)
●
●
●
●
●
●
●
●
160.3
163.5
133.6
136.3
146.9
149.9
41036/f
EOSC
80.3
66.9
73.6
20556/f
EOSC
81.9
68.2
75.1
Conversion Time for 2x Speed Mode
MIN
0
0.6
1.3
0.6
0.6
0
100
20+0.1C
B
20+0.1C
B
0.6
TYP
MAX
400
UNITS
kHz
µs
µs
µs
µs
0.9
300
300
µs
ns
ns
ns
µs
Note 7:
50Hz mode (internal oscillator) or f
EOSC
= 256kHz
±2%
(external
oscillator).
Note 8:
60Hz mode (internal oscillator) or f
EOSC
= 307.2kHz
±2%
(external
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
0
pin. The
external oscillator frequency, f
EOSC
, 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:
C
B
= capacitance of one bus line in pF.
Note 15:
All values refer to V
IH(MIN)
and V
IL(MAX)
levels.
2485fa
5
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