and other sensors to be digitized by a single converter.
A fifth differential reference input can be selected for any
input channel not requiring ratiometric measurements
(thermocouples, voltages, current sense, etc.). The flex-
ible input multiplexer allows single-ended or differential
inputs coupled with a slaved reference input or a universal
reference input.
A proprietary delta-sigma architecture results in absolute
accuracy (offset, full-scale, linearity) of 15ppm, noise as
low as 200nV
RMS
and speeds as high as 8kHz. Through
a simple 4-wire interface, ten speed/resolution combina-
tions can be selected. The first conversion following a
speed, resolution, channel change or reference change is
valid since there is no settling time between conversions,
enabling scan rates of up to 4kHz. Additionally, a 2× mode
can be selected for any speed-enabling output rates up to
8kHz with one cycle of latency.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. patents, including 6140950, 6169506, 6208279, 6411242, 6639526.
n
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n
Five Selectable Differential Reference Inputs
Four Differential/Eight Single-Ended Inputs
4-Way MUX for Multiple Ratiometric
Measurements
Up to 8kHz Output Rate (External f
O
)
Up to 4kHz Multiplexing Rate (External f
O
)
Selectable Speed/Resolution:
2µV
RMS
Noise at 1.76kHz Output Rate
200nV
RMS
Noise at 13.8Hz Output Rate with
Simultaneous 50/60Hz Rejection
Guaranteed Modulator Stability and Lock-Up
Immunity for any Input and Reference Conditions
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 Mode, Each Conversion is Accurate Even
After a New Channel is Selected
Internal Oscillator—No External Components
LTC2447 Includes MUXOUT/ADCIN for External
Buffering or Gain
Tiny QFN 5mm × 7mm Package
Flow
Weight Scales
Pressure
Direct Temperature Measurement
Gas Chromatography
APPLICATIONS
n
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TYPICAL APPLICATION
Multiple Ratiometric Measurement System
V
CC
REF
+
IN
+
•
•
•
19-INPUT
4-OUTPUT
MUX
CS
VARIABLE SPEED/
RESOLUTION 24-BIT
∆Σ ADC
SDI
SDO
SCK
LTC2446
RMS NOISE (µV)
LTC2446 RMS Noise vs Speed
100
V
CC
= 5V
V
REF
= 5V
V
IN+
= V
IN–
= 0V
2× SPEED MODE
NO LATENCY MODE
2.8V AT 880Hz
280nV AT 6.9Hz
(50/60Hz REJECTION)
10
+
–
1
IN
–
REF
–
0.1
1
1000
10
100
CONVERSION RATE (Hz)
10000
24467 TA02
24467 TA01
24467fb
For more information
www.linear.com/LTC2446
1
LTC2446/LTC2447
ABSOLUTE MAXIMUM RATINGS
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
LTC2446C/LTC2447C .............................. 0°C to 70°C
LTC2446I/LTC2447I ............................–40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
PIN CONFIGURATION
LTC2446
SDO
SCK
TOP VIEW
GND
GND
SDI
CS
F
O
LTC2447
SDO
SCK
TOP VIEW
GND
GND
31 GND
30 REFG
–
29 REFG
+
28 V
CC
27 MUXOUTN
39
26 ADCINN
25 ADCINP
24 MUXOUTP
23 V
REF67+
22 V
REF67–
21 CH7
20 CH6
13 14 15 16 17 18 19
_
38 37 36 35 34 33 32
GND 1
BUSY 2
EXT
3
GND 4
GND 5
GND 6
COM 7
CH0 8
CH1 9
V
REF01–
10
V
REF01+
11
CH2 12
13 14 15 16 17 18 19
–
38 37 36 35 34 33 32
31 GND
30 REFG
28 V
CC
27 NC
26 NC
25 NC
24 NC
23 V
REF67+
22 V
REF67–
21 CH7
20 CH6
–
GND 1
BUSY 2
EXT
3
GND 4
GND 5
GND 6
COM 7
CH0 8
CH1 9
V
REF01–
10
V
REF01+
11
CH2 12
V
REF23+
V
REF45–
CH4
CH3
CH5
+
29 REFG
+
39
V
REF23+
–
V
REF23
V
REF45
V
REF45+
CH4
CH3
CH5
V
REF23
SDI
CS
F
O
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC2446CUHF#PBF
LTC2446IUHF#PBF
LTC2447CUHF#PBF
LTC2447IUHF#PBF
TAPE AND REEL
LTC2446CUHF#TRPBF
LTC2446IUHF#TRPBF
LTC2447CUHF#TRPBF
LTC2447IUHF#TRPBF
http://www.linear.com/product/LTC2446#orderinfo
PART MARKING
2446
2446
2447
2447
PACKAGE DESCRIPTION
38-LEAD (5mm × 7mm) PLASTIC QFN
38-LEAD (5mm × 7mm) PLASTIC QFN
38-LEAD (5mm × 7mm) PLASTIC QFN
38-LEAD (5mm × 7mm) PLASTIC QFN
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
V
REF45
24467fb
2
For more information
www.linear.com/LTC2446
LTC2446/LTC2447
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 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
Negative Full-Scale Error
Negative Full-Scale Error Drift
Total Unadjusted Error
CONDITIONS
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)
2.5V ≤ REF
+
≤ V
CC
, REF
–
= GND, GND ≤ IN
–
= IN
+
≤ V
CC
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ELECTRICAL CHARACTERISTICS
MIN
24
TYP
5
3
2.5
20
10
10
0.2
10
10
0.2
15
15
15
120
MAX
15
5
50
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
50
50
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
Input Common Mode Rejection DC
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–)
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
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
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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
2
2
2
2
–15
1
15
I
DC_LEAK(IN+, IN–, REF+, REF–)
Leakage Current, Inputs and Reference
CS
= V
CC
, IN
+
= GND, IN
–
= GND,
l
REF
+
= 5V, REF
–
= GND
I
SAMPLE(IN+, IN–, REF+, REF–)
Average Input/Reference Current
During Sampling
t
OPEN
QIRR
MUX Break-Before-Make
MUX Off Isolation
V
IN
= 2V
P-P
DC to 1.8MHz
nA
nA
ns
dB
Varies, See Applications Section
50
120
24467fb
For more information
www.linear.com/LTC2446
3
LTC2446/LTC2447
The
l
denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
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
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
, EXT, SDI
Digital Input Current
SCK
Digital Input Capacitance
CS,
F
O
, SDI
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)
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DIGITAL INPUTS AND DIGITAL OUTPUTS
CONDITIONS
4.5V ≤ V
CC
≤ 5.5V
4.5V ≤ V
CC
≤ 5.5V
MIN
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TYP
MAX
UNITS
V
2.5
0.8
2.5
0.8
–10
–10
10
10
V
CC
– 0.5V
0.4
V
CC
– 0.5V
0.4
–10
10
10
10
V
V
V
µA
µA
pF
pF
V
V
V
V
µA
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)
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
Conversion Mode
Sleep Mode
CS
= 0V (Note 7)
CS
= V
CC
(Note 7)
CONDITIONS
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POWER REQUIREMENTS
MIN
4.5
TYP
MAX
5.5
UNITS
V
mA
µA
8
8
11
30
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV
PARAMETER
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time
OSR = 256
OSR = 32768
External Oscillator, 1× Mode
(Notes 10, 13)
f
ISCK
Internal SCK Frequency
Internal Oscillator (Note 9)
External Oscillator (Notes 9, 10)
CONDITIONS
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TIMING CHARACTERISTICS
MIN
0.1
25
25
0.99
126
TYP
MAX
12
10000
10000
UNITS
MHz
ns
ns
ms
ms
ms
1.13
145
40 • OSR + 178
f
EOSC
(KHz)
1.33
170
0.8
0.9
f
EOSC
/10
1
MHz
Hz
24467fb
4
For more information
www.linear.com/LTC2446
LTC2446/LTC2447
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
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
6
t
7
t
8
PARAMETER
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 Setup Before
CS
↓
SCK Hold After
CS
↓
SDI Setup Before SCK
↑
SDI Hold After SCK
↑
(Note 5)
(Note 5)
(Note 5)
CONDITIONS
(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)
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TIMING CHARACTERISTICS
MIN
45
25
25
41.6
TYP
MAX
55
20
UNITS
%
MHz
ns
ns
35.3
320/f
EOSC
32/f
ESCK
30.9
µs
s
s
ns
ns
µs
ns
0
0
5
25
25
25
25
15
50
50
10
10
ns
ns
ns
ns
ns
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
CC
= 4.5V to 5.5V unless otherwise specified.
V
REF
= REF
+
– REF
–
, V
REFCM
= (REF
+
+ REF
–
)/2; REF
+
is the positive
reference input, REF
–
is the negative reference input; 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 Hz.
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 5 to 15 f
O
cycles
to the conversion time.
PIN FUNCTIONS
GND (Pins 1, 4, 5, 6, 31, 32, 33):
Ground. Multiple ground
pins internally connected for optimum ground current flow
and V
CC
decoupling. Connect each one of these pins to
a common ground plane through a low impedance con-
nection. All seven pins must be connected to ground for
proper operation.
BUSY (Pin 2):
Conversion in Progress Indicator. This pin
is HIGH while the conversion is in progress and goes LOW
indicating the conversion is complete and data is ready.
It remains LOW during the sleep and data output states.
At the conclusion of the data output state, it goes HIGH
indicating a new conversion has begun.
EXT
(Pin 3):
Internal/External SCK Selection Pin. This
pin is used to select internal or external SCK for output-
ting/inputting data. If
EXT
is tied low, the device is in the
external SCK mode and data is shifted out of the device
under the control of a user applied serial clock. If
EXT
is
tied high, the internal serial clock mode is selected. The
device generates its own SCK signal and outputs this on
the SCK pin. A framing signal BUSY (Pin 2) goes low
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