LTC2488
16-Bit 2-/4-Channel
ΔΣ
ADC with Easy Drive Input
Current Cancellation
FEATURES
■
■
DESCRIPTION
The LTC
®
2488 is a 4-channel (2-channel differential), 16-
bit, No Latency
ΔΣ™
ADC with Easy Drive™ technology.
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 rail-to-
rail input signals to be directly digitized while maintaining
exceptional DC accuracy.
The LTC2488 includes an integrated oscillator. This device
can be configured to measure an external signal from
combinations of 4 analog input channels operating in single
ended or differential modes. It automatically rejects line
frequencies of 50Hz and 60Hz simultaneously.
The LTC2488 allows a wide common mode, input range
(0V to V
CC
), independent of the reference voltage. Any
combination of single-ended or differential inputs can
be selected and the first conversion after a new channel
selection is valid.
, 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.
■
■
■
■
■
■
■
■
■
■
Up to 2 Differential or 4 Single-Ended Inputs
Easy Drive Technology Enables Rail-to-Rail Inputs
with Zero Differential Input Current
Directly Digitizes High Impedance Sensors with
Full Accuracy
600nV RMS Noise (0.02LSB Transition Noise)
GND to V
CC
Input/Reference Common Mode Range
Simultaneous 50Hz/60Hz Rejection
2ppm INL, No Missing Codes
1ppm Offset and 15ppm Full-Scale Error
No Latency: Digital Filter Settles in a Single Cycle,
Even After a New Channel is Selected
Single Supply 2.7V to 5.5V Operation (0.8mW)
Internal Oscillator
Tiny 4mm
×
3mm DFN Package
APPLICATIONS
■
■
■
■
Direct Sensor Digitizer
Direct Temperature Measurement
Instrumentation
Industrial Process Control
TYPICAL APPLICATION
Data Acquisition System
2.7V TO 5.5V
10µF
0.1µF
+FS ERROR (ppm)
Fullscale Error vs Source Resistance
80
V
CC
= 5V
60 V
REF
= 5V
V
IN+
= 3.75V
–
40 V
IN
= 1.25V
F
O
= GND
T
A
= 25°C
20
C
IN
= 1µF
0
–20
–40
–60
F
O
–80
1
2488 TA01a
CH0
CH1
REF
+
V
CC
4-CHANNEL
MUX
CH2
CH3
COM
IN
+
16-BIT
∆Σ
ADC
WITH EASY DRIVE
IN
–
REF
–
SDI
SCK
SDO
CS
4-WIRE
SPI INTERFACE
OSC
10
100
1k
R
SOURCE
(Ω)
10k
100k
2488 TA01b
2488f
1
LTC2488
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
PACKAGE/ORDER INFORMATION
F
O
SDI
SCK
CS
SDO
GND
COM
1
2
3
4
5
6
7
15
14 REF
–
13 REF
+
12 V
CC
11 CH3
10 CH2
9 CH1
8 CH0
Supply Voltage (V
CC
) ................................... –0.3V to 6V
Analog Input Voltage
(CH0 to CH3, COM) ..................–0.3V to (V
CC
+ 0.3V)
REF
+
, REF
–
................................–0.3V to (V
CC
+ 0.3V)
Digital Input Voltage......................–0.3V to (V
CC
+ 0.3V)
Digital Output Voltage ...................–0.3V to (V
CC
+ 0.3V)
Operating Temperature Range
LTC2488C ................................................ 0°C to 70°C
LTC2488I ............................................. –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
DE PACKAGE
14-LEAD (4mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC2488CDE
LTC2488IDE
DE PART MARKING*
2488
2488
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
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
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3, 4)
MIN
16
●
●
TYP
2
1
0.5
10
MAX
20
5
32
UNITS
Bits
ppm of V
REF
ppm of V
REF
µV
nV/°C
ppm of V
REF
ppm of V
REF
/°C
ppm of V
REF
ppm of V
REF
/°C
ppm of V
REF
ppm of V
REF
ppm of V
REF
µV
RMS
0.1V ≤ 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 14)
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
+
= 0.25V
REF
, IN
–
= 0.75V
REF
2.5V ≤ V
REF
≤ V
CC
, IN
+
= 0.25V
REF
, IN
–
= 0.75V
REF
5V ≤ V
CC
≤ 5.5V, V
REF
= 2.5V, V
IN(CM)
= 1.25V
5V ≤ V
CC
≤ 5.5V, V
REF
= 5V, V
IN(CM)
= 2.5V
2.7V ≤ V
CC
≤ 5.5V, V
REF
= 2.5V, V
IN(CM)
= 1.25V
2.7V < V
CC
< 5.5V, 2.5V ≤ V
REF
≤ V
CC
,
GND ≤ IN
+
= IN
–
≤ V
CC
(Note 13)
●
●
0.1
32
0.1
15
15
15
0.6
Output Noise
2488f
2
LTC2488
CONVERTER CHARACTERISTICS
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)
●
●
●
●
●
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
MIN
140
140
140
110
110
87
120
140
120
120
120
120
120
TYP
MAX
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
ANALOG INPUT AND REFERENCE
SYMBOL
IN
+
IN
–
V
IN
FS
LSB
REF
+
REF
–
V
REF
C
S(IN+)
C
S(IN–)
C
S(VREF)
I
DC_LEAK(IN+)
I
DC_LEAK(IN–)
I
DC_LEAK(REF
t
OPEN
QIRR
+
)
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
PARAMETER
Absolute/Common Mode IN
+
Voltage
(IN
+
Corresponds to the Selected Positive Input Channel)
Absolute/Common Mode IN
–
Voltage
(IN
–
Corresponds to the Selected Negative Input Channel)
Input Differential Voltage Range (IN
+
– IN
–
)
Full Scale of the Differential Input (IN
+
– IN
–
)
Least Significant Bit of the Output Code
Absolute/Common Mode REF
+
Voltage
Absolute/Common Mode REF
–
Voltage
Reference Voltage Range (REF
+
– REF
–
)
IN
+
Sampling Capacitance
IN
–
Sampling Capacitance
V
REF
Sampling Capacitance
IN
+
DC Leakage Current
IN
–
DC Leakage Current
REF
+
DC Leakage Current
MUX Break-Before-Make
MUX Off Isolation
V
IN
= 2V
P-P
DC to 1.8MHz
Sleep Mode, IN
+
= GND
Sleep Mode, IN
–
= GND
Sleep Mode, REF
+
= V
CC
CONDITIONS
MIN
GND – 0.3V
GND – 0.3V
●
●
●
●
●
●
TYP
MAX
V
CC
+ 0.3V
V
CC
+ 0.3V
+FS
UNITS
V
V
V
V
–FS
0.5V
REF
FS/2
16
0.1
GND
0.1
11
11
11
V
CC
+
– 0.1V
REF
V
CC
V
V
V
pF
pF
pF
●
●
●
●
–10
–10
–100
–100
1
1
1
1
50
120
10
10
100
100
nA
nA
nA
nA
ns
dB
I
DC_LEAK(REF–)
REF
–
DC Leakage Current
Sleep Mode, REF
–
= GND
2488f
3
LTC2488
DIGITAL INPUTS AND DIGITAL OUTPUTS
SYMBOL
V
IH
V
IL
V
IH
V
IL
I
IN
I
IN
C
IN
C
IN
V
OH
V
OL
V
OH
V
OL
I
OZ
PARAMETER
High Level Input Voltage (
⎯
C
⎯
S, F
O
, SDI)
Low Level Input Voltage (
⎯
C
⎯
S, F
O
, SDI)
High Level Input Voltage (SCK)
Low Level Input Voltage (SCK)
⎯ ⎯
Digital Input Current (CS, F
O
, SDI)
Digital Input Current (SCK)
⎯
Digital Input Capacitance (C
⎯
S, F
O
, SDI)
Digital Input Capacitance (SCK)
High Level Output Voltage (SDO)
Low Level Output Voltage (SDO)
High Level Output Voltage (SCK)
Low Level Output Voltage (SCK)
Hi-Z Output Leakage (SDO)
CONDITIONS
2.7V ≤ V
CC
≤ 5.5V
2.7V ≤ V
CC
≤ 5.5V
2.7V ≤ V
CC
≤ 5.5V (Notes 10, 15)
2.7V ≤ V
CC
≤ 5.5V (Notes 10, 15)
0V ≤ V
IN
≤ V
CC
0V ≤ V
IN
≤ V
CC
(Notes 10, 15)
(Notes 10, 15)
I
O
= –800µA
I
O
= 1.6mA
I
O
= –800µA (Notes 10, 17)
I
O
= 1.6mA (Notes 10, 17)
●
●
●
●
●
●
●
●
●
●
●
The
●
denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
MIN
V
CC
– 0.5
0.5
V
CC
– 0.5
0.5
–10
–10
10
10
V
CC
– 0.5
0.4
V
CC
– 0.5
0.4
–10
10
10
10
TYP
MAX
UNITS
V
V
V
V
µA
µA
pF
pF
V
V
V
V
µA
POWER REQUIREMENTS
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
●
MIN
2.7
●
●
TYP
160
1
MAX
5.5
275
2
UNITS
V
µA
µA
Conversion Current (Note 12)
Sleep Mode (Note 12)
2488f
4
LTC2488
DIGITAL INPUTS AND DIGITAL OUTPUTS
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV
f
ISCK
D
ISCK
f
ESCK
t
LESCK
t
HESCK
t
DOUT_ISCK
t
DOUT_ESCK
t
1
t
2
t
3
t
4
t
KQMAX
t
KQMIN
t
5
t
7
t
8
PARAMETER
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time
Internal SCK Frequency
Internal SCK Duty Cycle
External SCK Frequency Range
External SCK Low Period
External SCK High Period
Internal SCK 24-Bit Data Output Time
External SCK 24-Bit Data Output Time
⎯
C
⎯
S
↓
to SDO Low
⎯
C
⎯
S
↑
to SDO High Z
⎯
C
⎯
S
↓
to SCK↓
⎯
CS
↓
to SCK↑
⎯
SCK↓ to SDO Valid
SDO Hold After SCK↓
SCK Set-Up Before
⎯
C
⎯
S
↓
SDI Setup Before SCK↑
SDI Hold After SCK↑
(Note 5)
(Note 5)
(Note 5)
Internal SCK Mode
External SCK Mode
Simultaneous 50Hz/60Hz
External Oscillator
Internal Oscillator (Notes 10, 17)
External Oscillator (Notes 10, 11, 15)
(Notes 10, 17)
(Notes 10, 11, 15)
(Notes 10, 11, 15)
(Notes 10, 11, 15)
Internal Oscillator (Notes 10, 17)
External Oscillator (Notes 10, 11, 15)
●
●
●
●
●
The
●
denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
(Note 16)
●
●
●
●
MIN
10
0.125
0.125
144.1
TYP
MAX
4000
100
100
UNITS
kHz
µs
µs
ms
ms
kHz
kHz
146.9
41036/f
EOSC
(in kHz)
38.4
f
EOSC
/8
149.9
45
125
125
0.61
0.625
192/f
EOSC
(in kHz)
24/f
ESCK
(in kHz)
55
4000
%
kHz
ns
ns
0.64
ms
ms
ms
ns
ns
ns
ns
ns
ns
ns
ns
ns
●
●
●
●
●
●
●
●
●
0
0
0
50
200
200
200
200
15
50
100
100
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:
Unless otherwise specified:
V
CC
= 2.7V to 5.5V
V
REFCM
= V
REF
/2, F
S
= 0.5V
REF
V
IN
= IN
+
– IN
–
, V
IN(CM)
= (IN
+
– IN
–
)/2,
where IN
+
and IN
–
are the selected input channels.
Note 4:
Use internal conversion clock or external conversion clock source
with f
EOSC
= 307.2kHz unless other wise 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:
f
EOSC
= 256kHz ±2% (external oscillator).
Note 8:
f
EOSC
= 307.2kHz ±2% (external oscillator).
Note 9:
Simultaneous 50Hz/60Hz (internal oscillator) or f
EOSC
= 280kHz
±2% (external oscillator).
Note 10:
The SCK can be configured in external SCK mode or internal SCK
mode. In external SCK mode, the SCK pin is used as a digital input and the
driving clock is f
ESCK
. In the internal SCK mode, the SCK pin is used as a
digital output and the output clock signal during the data output is f
ISCK
.
Note 11:
The external oscillator is connected to the F
O
pin. The external
oscillator frequency, f
EOSC
, is expressed in kHz.
Note 12:
The converter uses its internal oscillator.
Note 13:
The output noise includes the contribution of the internal
calibration operations. V
REF
≤ V
CC
.
Note 14:
Guaranteed by design and test correlation.
Note 15:
The converter is in external SCK mode of operation such that the
SCK pin is used as a digital input. The frequency of the clock signal driving
SCK during the data output is f
ESCK
and is expressed in Hz.
Note 16:
Refer to Applications Information section for performance vs
data rate graphs.
Note 17:
The converter in internal SCK mode of operation such that the
SCK pin is used as a digital output.
2488f
5
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