FEATURES
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LTC2440
24-Bit High Speed
Differential
Δ∑
ADC with
Selectable Speed/Resolution
DESCRIPTION
The LTC
®
2440 is a high speed 24-bit No Latency Δ∑
TM
ADC with 5ppm INL and 5μV offset. It uses proprietary
delta-sigma architecture enabling variable speed and reso-
lution with no latency. Ten speed/resolution combinations
(6.9Hz/200nV
RMS
to 3.5kHz/25μV
RMS
) are programmed
through a simple serial interface. Alternatively, by tying a
single pin HIGH or LOW, a fast (880Hz/2μV
RMS
) or ultralow
noise (6.9Hz, 200nV
RMS
, 50/60Hz rejection) speed/reso-
lution combination can be easily selected. The accuracy
(offset, full-scale, linearity, drift) and power dissipation
are independent of the speed selected. Since there is no
latency, a speed/resolution change may be made between
conversions with no degradation in performance.
Following each conversion cycle, the LTC2440 automati-
cally enters a low power sleep state. Power dissipation
may be reduced by increasing the duration of this sleep
state. For example, running at the 3.5kHz conversion speed
but reading data at a 100Hz rate draws 240μA average
current (1.1mW) while reading data at a 7Hz output rate
draws only 25μA (125μW).The LTC2440 communicates
through a flexible 3-wire or 4-wire digital interface that is
compatible with the LTC2410 and is available in a narrow
16-lead SSOP package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No Latency Δ∑ is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
Up to 3.5kHz Output Rate
Selectable Speed/Resolution
2μV
RMS
Noise at 880Hz Output Rate
200nV
RMS
Noise at 6.9Hz Output Rate with
Simultaneous 50/60Hz Rejection
0.0005% INL, No Missing Codes
Autosleep Enables 20μA Operation at 6.9Hz
<5μV Offset (4.5V < V
CC
< 5.5V, –40°C to 85°C)
Differential Input and Differential Reference with
GND to V
CC
Common Mode Range
No Latency, Each Conversion is Accurate Even After
an Input Step
Internal Oscillator—No External Components
Pin Compatible with the LTC2410
24-Bit ADC in Narrow 16-Lead SSOP Package
APPLICATIONS
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High Speed Multiplexing
Weight Scales
Auto Ranging 6-Digit DVMs
Direct Temperature Measurement
High Speed Data Acquisition
TYPICAL APPLICATION
Simple 24-Bit 2-Speed Acquisition System
4.5V TO 5.5V
Speed vs RMS Noise
100
V
CC
= 5V
V
REF
= 5V
V
IN+
= V
IN–
= 0V
V
CC
REFERENCE VOLTAGE
0.1V TO V
CC
ANALOG INPUT
–0.5V
REF
TO 0.5V
REF
BUSY
LTC2440
f
O
REF
+
4
REF
–
IN
+
IN
–
RMS NOISE (μV)
10
2μV AT 880Hz
200nV AT 6.9Hz
1 (50/60Hz REJECTION)
SCK
SDO
CS
SDI
3-WIRE
SPI INTERFACE
V
CC
6.9Hz, 200nV NOISE,
50/60Hz REJECTION
10-SPEED SERIAL
PROGRAMMABLE
880Hz OUTPUT RATE,
2μV NOISE
2440 TA01
GND
EXT
2440 TA01
0.1
1
1000
10
100
CONVERSION RATE (Hz)
10000
2440 TA02
2440fd
1
LTC2440
ABSOLUTE MAXIMUM RATINGS
(Notes 1,2)
PIN CONFIGURATION
TOP VIEW
GND
V
CC
REF
+
REF
–
IN
+
IN
–
SDI
GND
1
2
3
4
5
6
7
8
16 GND
15 BUSY
14 f
O
13 SCK
12 SDO
11 CS
10 EXT
9
GND
Supply Voltage (V
CC
) to GND ....................... –0.3V to 6V
Analog Input Pins Voltage
to GND ......................................–0.3V to (V
CC
+ 0.3V)
Reference Input Pins 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
LTC2440C ............................................... 0°C to 70°C
LTC2440I .............................................–40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC2440CGN#PBF
LTC2440IGN#PBF
TAPE AND REEL
LTC2440CGN#TRPBF
LTC2440IGN#TRPBF
PART MARKING
2440
2440I
PACKAGE DESCRIPTION
Narrow 16-Lead SSOP
Narrow 16-Lead SSOP
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
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
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3, 4)
MIN
l
l
l
l
l
l
l
TYP
5
3
2.5
20
10
10
0.2
10
10
0.2
15
15
15
120
MAX
15
5
30
50
30
50
UNITS
Bits
ppm of V
REF
ppm of V
REF
μV
nV/ °C
ppm of V
REF
ppm of V
REF
ppm of V
REF
/°C
ppm of V
REF
ppm of V
REF
ppm of V
REF
/°C
ppm of V
REF
ppm of V
REF
ppm of V
REF
dB
2440fd
0.1V ≤ V
REF
≤ V
CC
, –0.5 • V
REF
≤ V
IN
≤ 0.5 • V
REF
, (Note 5)
V
CC
= 5V, REF
+
= 5V, REF
–
= GND, V
INCM
= 2.5V, (Note 6)
REF
+
= 2.5V, REF
–
= GND, V
INCM
= 1.25V, (Note 6)
2.5V ≤ REF
+
≤ V
CC
, REF
–
= GND, GND ≤ IN
+
= IN
–
≤ V
CC
(Note 12)
2.5V ≤ REF
+
≤ V
CC
, REF
–
= GND, GND ≤ IN
+
= IN
–
≤ V
CC
REF
+
= 5V, REF
–
= GND, IN
+
= 3.75V, IN
–
= 1.25V
REF
+
= 2.5V, REF
–
= GND, IN
+
= 1.875V, IN
–
= 0.625V
2.5V ≤ REF
+
≤ V
CC
, REF
–
= GND, IN
+
= 0.75REF
+
, IN
–
= 0.25 • REF
+
REF
+
= 5V, REF
–
= GND, IN
+
= 1.25V, IN
–
= 3.75V
REF
+
= 2.5V, REF
–
= GND, IN
+
= 0.625V, IN
–
= 1.875V
2.5V ≤ REF
+
≤ V
CC
, REF
–
= GND, IN
+
= 0.25 • REF
+
, IN
–
= 0.75 • REF
+
5V ≤ V
CC
≤ 5.5V, REF
+
= 2.5V, REF
–
= GND, V
INCM
= 1.25V
5V ≤ V
CC
≤ 5.5V, REF
+
= 5V, REF
–
= GND, V
INCM
= 2.5V
REF
+
= 2.5V, REF
–
= GND, V
INCM
= 1.25V, (Note 6)
24
Input Common Mode Rejection DC 2.5V ≤ REF
+
≤ V
CC
, REF
–
= GND, GND ≤ IN
–
= IN
+
≤ V
CC
2
LTC2440
ANALOG INPUT AND REFERENCE
SYMBOL
IN
+
IN
–
V
IN
REF
+
REF
–
V
REF
C
S(IN
+
)
C
S(IN
–
)
C
S(REF
+
)
C
S(REF
–
)
I
DC_LEAK(IN
+
, IN
–
,
REF
+
, REF
–
)
The
l
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
Absolute/Common Mode IN
–
Voltage
Input Differential Voltage Range (IN
+
– IN
–
)
Absolute/Common Mode REF
+
Voltage
Absolute/Common Mode REF
–
Voltage
Reference Differential Voltage Range (REF
+
– REF
–
)
IN
+
Sampling Capacitance
IN
–
Sampling Capacitance
REF
+
Sampling Capacitance
REF
–
Sampling Capacitance
Leakage Current, Inputs and Reference
Average Input/Reference Current During
Sampling
CS
= V
CC
, IN
+
= GND, IN
–
= GND,
REF
+
= 5V, REF
–
= GND
l
CONDITIONS
l
l
l
l
l
l
MIN
GND – 0.3V
GND – 0.3V
–V
REF
/ 2
0.1
GND
0.1
TYP
MAX
V
CC
+ 0.3V
V
CC
+ 0.3V
V
REF
/ 2
V
CC
V
CC
– 0.1V
V
CC
UNITS
V
V
V
V
V
V
pF
pF
pF
pF
3.5
3.5
3.5
3.5
–100
10
100
nA
I
SAMPLE(IN
+
, IN
–
,
REF
+
, REF
–
)
Varies, See Applications Section
DIGITAL INPUTS AND DIGITAL OUTPUTS
SYMBOL
V
IN
V
IL
V
IN
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
CS,
f
O
, SDI
Low Level Input Voltage
CS,
f
O
, SDI
High Level Input Voltage
SCK
Low Level Input Voltage
SCK
Digital Input Current
CS,
f
O
Digital Input Current
SCK
Digital Input Capacitance
CS,
f
O
Digital Input Capacitance
SCK
High Level Output Voltage
SDO, BUSY
Low Level Output Voltage
SDO, BUSY
High Level Output Voltage
SCK
Low Level Output Voltage
SCK
Hi-Z Output Leakage
SDO
(Note 8)
I
O
= –800μA
I
O
= 1.6mA
I
O
= –800μA (Note 9)
I
O
= 1.6mA (Note 9)
CONDITIONS
4.5V ≤ V
CC
≤ 5.5V
4.5V ≤ V
CC
≤ 5.5V
The
l
denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
MIN
l
l
l
l
l
l
TYP
MAX
UNITS
V
2.5
0.8
2.5
0.8
–10
–10
10
10
10
10
V
V
V
μA
μA
pF
pF
V
4.5V ≤ V
CC
≤ 5.5V (Note 8)
4.5V ≤ V
CC
≤ 5.5V (Note 8)
0V ≤ V
IN
≤ V
CC
0V ≤ V
IN
≤ V
CC
(Note 8)
l
l
l
l
l
V
CC
– 0.5V
0.4V
V
CC
– 0.5V
0.4V
–10
10
V
V
V
μA
2440fd
3
LTC2440
POWER REQUIREMENTS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
Conversion Mode
Sleep Mode
CS
= 0V (Note 7)
CS
= V
CC
(Note 7)
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
l
l
l
MIN
4.5
TYP
MAX
5.5
UNITS
V
mA
μA
8
8
11
30
TIMING CHARACTERISTICS
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV
PARAMETER
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
MIN
0.1
25
25
0.99
126
TYP
MAX
20
10000
10000
UNITS
MHz
ns
ns
ms
ms
ms
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time
OSR = 256 (SDI = 0)
OSR = 32768 (SDI = 1)
External Oscillator (Note 10, 13)
1.13
145
40 • OSR + 170
f
EOSC
(kHz)
1.33
170
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
Internal SCK Frequency
Internal SCK Duty Cycle
External SCK Frequency Range
External SCK Low Period
External SCK High Period
Internal SCK 32-Bit Data Output Time
External SCK 32-Bit Data Output Time
CS
to SDO Low Z
CS
↑
to SDO High Z
CS
to SCK
↑
↑
CS
to SCK
↑
SCK to SDO Valid
SDO Hold After SCK
SCK Set-Up Before
CS
SDI Hold After SCK
↑
↑
↑
↑
↑
↑
Internal Oscillator (Note 9)
External Oscillator (Notes 9, 10)
(Note 9)
(Note 8)
(Note 8)
(Note 8)
Internal Oscillator (Notes 9, 11)
External Oscillator (Notes 9, 10)
(Note 8)
(Note 12)
(Note 12)
(Note 9)
(Notes 8, 12)
(Note 5)
(Note 5)
(Note 5)
0.8
45
25
25
30.9
0.9
f
EOSC
/10
1
55
20
%
MHz
ns
ns
35.3
320/f
EOSC
32/f
ESCK
41.6
μs
s
s
ns
ns
μs
ns
0
0
5
25
25
25
25
15
50
10
10
ns
ns
ns
ns
ns
l
l
l
l
SDI Setup Before SCK
↑
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
= 4.5 to 5.5V unless otherwise specified.
V
REF
= REF
+
– REF
–
, V
REFCM
= (REF
+
+ REF
–
)/2;
V
IN
= IN
+
– IN
–
, V
INCM
= (IN
+
+ IN
–
)/2.
Note 4:
f
O
pin tied to GND or to external conversion clock source with
f
EOSC
= 10MHz 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:
The converter uses the internal oscillator.
Note 8:
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 9:
The converter is in internal SCK mode of operation such that the
SCK pin is used as a digital output. In this mode of operation, the SCK pin
.
has a total equivalent load capacitance of C
LOAD
= 20pF
Note 10:
The external oscillator is connected to the f
O
pin. The external
oscillator frequency, f
EOSC
, is expressed in kHz.
Note 11:
The converter uses the internal oscillator. f
O
= 0V.
Note 12:
Guaranteed by design and test correlation.
Note 13:
There is an internal reset that adds an additional 1μs (typical) to
the conversion time.
2440fd
4
LTC2440
TYPICAL PERFORMANCE CHARACTERISTICS
Integral Nonlinearity f
OUT
= 3.5kHz
10
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
INL ERROR (ppm OF V
REF
)
10
Integral Nonlinearity
f
OUT
= 1.76kHz
10
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
Integral Nonlinearity f
OUT
= 880Hz
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
INL ERROR (ppm OF V
REF
)
INL ERROR (ppm OF V
REF
)
0
0
0
–5
–5
–5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
2440 G01
2440 G02
2440 G03
Integral Nonlinearity f
OUT
= 440Hz
10
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
INL ERROR (ppm OF V
REF
)
10
Integral Nonlinearity f
OUT
= 220Hz
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
10
Integral Nonlinearity f
OUT
= 110Hz
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
INL ERROR (ppm OF V
REF
)
INL ERROR (ppm OF V
REF
)
0
0
0
–5
–5
–5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
2440 G04
2440 G05
2440 G06
Integral Nonlinearity f
OUT
= 55Hz
10
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
10
Integral Nonlinearity f
OUT
= 27.5Hz
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
INL ERROR (ppm OF V
REF
)
10
Integral Nonlinearity
f
OUT
= 13.75Hz
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
V
INCM
= 2.5V
f
O
= GND
T
A
= 25°C
INL ERROR (ppm OF V
REF
)
INL ERROR (ppm OF V
REF
)
V
CC
= 5V
V
REF
= 5V
V
REF+
= 5V
–
5 V
REF
= GND
0
0
0
–5
–5
–5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
–10
–2.5 –2 –1.5 –1 –0.5 0 0.5 1
V
IN
(V)
1.5 2
2.5
2440 G07
2440 G08
2440 G09
2440fd
5
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