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LTC2444/LTC2445/
LTC2448/LTC2449
24-Bit High Speed
8-/16-Channel ∆Σ ADCs with
Selectable Speed/Resolution
FEATURES
Up to 8 Differential or 16 Single-Ended Input
Channels
Up to 8kHz Output Rate
Up to 4kHz Multiplexing Rate
Selectable Speed/Resolution
2µVRMS Noise at 1.76kHz Output Rate
200nVRMS 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 < VCC < 5.5V, – 40°C to 85°C)
Differential Input and Differential Reference with
GND to VCC Common Mode Range
No Latency Mode, Each Conversion is Accurate Even
After a New Channel is Selected
Internal Oscillator—No External Components
LTC2445/LTC2449 Include MUXOUT/ADCIN for
External Buffering or Gain
Tiny QFN 5mm xU7mm Package
APPLICATIO S
High Speed Multiplexing
Weight Scales
Auto Ranging 6-Digit DVMs
Direct Temperature Measurement
High Speed Data Acquisition
DESCRIPTIO
The LTC®2444/LTC2445/LTC2448/LTC2449 are 8-/16-
channel (4-/8-differential) high speed 24-bit No Latency
∆ΣTM ADCs. They use a proprietary delta-sigma architec-
ture enabling variable speed/resolution. Through a simple
4-wire serial interface, ten speed/resolution combinations
6.9Hz/280nVRMS to 3.5kHz/25µVRMS (4kHz with external
oscillator) can be selected with no latency between con-
version results or shift in DC accuracy (offset, full-scale,
linearity, drift). Additionally, a 2X speed mode can be
selected enabling output rates up to 7kHz (8kHz if an
external oscillator is used) with one cycle latency.
Any combination of single-ended or differential inputs can
be selected with a common mode input range from ground
to VCC, independent of VREF. While operating in the 1X
speed mode the first conversion following a new speed,
resolution, or channel selection is valid. Since there is no
settling time between conversions, all 8 differential chan-
nels can be scanned at a rate of 500Hz. At the conclusion
of each conversion, the converter is internally reset elimi-
nating any memory effects between successive conver-
sions and assuring stability of the high order delta-sigma
modulator.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No Latency ∆Σ is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
THERMOCOUPLE
Simple 24-Bit Variable Speed Data Acquisition System
4.5V TO 5.5V
CH0
CH1
CH7
CH8
CH15
COM
16-CHANNEL
MUX
REF+ VCC
FO
+
VARIABLE SPEED/
RESOLUTION
DIFFERENTIAL
24-BIT ∆Σ ADC
SDI
SCK
SDO
CS
1µF
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
(SIMULTANEOUS 50Hz/60Hz
REJECTION AT 6.9Hz OUTPUT RATE)
4-WIRE
SPI INTERFACE
REF
GND
LTC2448
2444 TA01
LTC2444/LTC2448
Speed vs RMS Noise
100
VCC = 5V
VVRINE+F
=
=
5V
VIN–
=
0V
2X SPEED MODE
NO LATENCY MODE
10
2.8µV AT 880Hz
280nV AT 6.9Hz
1 (50/60Hz REJECTION)
0.1
1
10 100 1000
CONVERSION RATE (Hz)
10000
2440 TA02
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LTC2444/LTC2445/
LTC2448/LTC2449
ABSOLUTE AXI U RATI GS
(Notes 1, 2)
Supply Voltage (VCC) to GND .......................– 0.3V to 6V
Analog Input Pins Voltage
to GND .................................... – 0.3V to (VCC + 0.3V)
Reference Input Pins 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)
UW U
PACKAGE/ORDER I FOR ATIO
Operating Temperature Range
LTC2444C/LTC2445C/
LTC2448C/LTC2449C .............................. 0°C to 70°C
LTC2444I/LTC2445I/
LTC2448I/LTC2449I ........................... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
TOP VIEW
GND 1
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
NC 8
CH0 9
CH1 10
NC 11
NC 12
38 37 36 35 34 33 32
13 14 15 16 17 18 19
31 GND
30 REF
29 REF+
28 VCC
27 NC
26 NC
25 NC
24 NC
23 NC
22 CH7
21 CH6
20 NC
ORDER PART
NUMBER
LTC2444CUHF
LTC2444IUHF
QFN PART MARKING*
2444
TOP VIEW
GND 1
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
NC 8
CH0 9
CH1 10
NC 11
NC 12
38 37 36 35 34 33 32
13 14 15 16 17 18 19
31 GND
30 REF
29 REF+
28 VCC
27 MUXOUTN
26 ADCINN
25 ADCINP
24 MUXOUTP
23 NC
22 CH7
21 CH6
20 NC
ORDER PART
NUMBER
LTC2445CUHF
LTC2445IUHF
QFN PART MARKING*
2445
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
TOP VIEW
GND 1
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
CH0 8
CH1 9
CH2 10
CH3 11
CH4 12
38 37 36 35 34 33 32
13 14 15 16 17 18 19
31 GND
30 REF
29 REF+
28 VCC
27 NC
26 NC
25 NC
24 NC
23 CH15
22 CH14
21 CH13
20 CH12
ORDER PART
NUMBER
LTC2448CUHF
LTC2448IUHF
QFN PART MARKING*
2448
GND 1
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
CH0 8
CH1 9
CH2 10
CH3 11
CH4 12
TOP VIEW
38 37 36 35 34 33 32
13 14 15 16 17 18 19
31 GND
30 REF
29 REF+
28 VCC
27 MUXOUTN
26 ADCINN
25 ADCINP
24 MUXOUTP
23 CH15
22 CH14
21 CH13
20 CH12
ORDER PART
NUMBER
LTC2449CUHF
LTC2449IUHF
QFN PART MARKING*
2449
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
*The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges.
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LTC2444/LTC2445/
LTC2448/LTC2449
ELECTRICAL CHARACTERISTICS The denotes 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
Negative Full-Scale Error
Negative Full-Scale Error Drift
Total Unadjusted Error
Input Common Mode Rejection DC
CONDITIONS
0.1V VREF VCC, –0.5 • VREF VIN 0.5 • VREF, (Note 5)
VCC = 5V, REF+ = 5V, REF= GND, VINCM = 2.5V, (Note 6)
REF+ = 2.5V, REF= GND, VINCM = 1.25V, (Note 6)
2.5V REF+ VCC, REF= GND,
GND IN+ = INVCC (Note 12)
2.5V REF+ VCC, REF= GND,
GND IN+ = INVCC
REF+ = 5V, REF= GND, IN+ = 3.75V, IN= 1.25V
REF+ = 2.5V, REF= GND, IN+ = 1.875V, IN= 0.625V
2.5V REF+ VCC, 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+ VCC, REF= GND,
IN+ = 0.25 • REF+, IN= 0.75 • REF+
5V VCC 5.5V, REF+ = 2.5V, REF= GND, VINCM = 1.25V
5V VCC 5.5V, REF+ = 5V, REF= GND, VINCM = 2.5V
REF+ = 2.5V, REF= GND, VINCM = 1.25V, (Note 6)
2.5V REF+ VCC, REF= GND,
GND IN= IN+ VCC
MIN TYP MAX
24
5 15
3
2.5 5
UNITS
Bits
ppm of VREF
ppm of VREF
µV
20 nV/°C
10 50
ppm of VREF
10 50
ppm of VREF
0.2 ppm of VREF/°C
10 50
ppm of VREF
10 50
ppm of VREF
0.2 ppm of VREF/°C
15 ppm of VREF
15 ppm of VREF
15 ppm of VREF
120 dB
U UU
U
A ALOG I PUT A D REFERE CE The denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
IN+
IN
VIN
REF+
REF
VREF
CS(IN+)
CS(IN–)
CS(REF+)
CS(REF–)
IDC_LEAK(IN+, IN–,
REF+, REF–)
ISAMPLE(IN+, IN–,
REF+, REF–)
tOPEN
QIRR
PARAMETER
Absolute/Common Mode IN+ Voltage
Absolute/Common Mode INVoltage
Input Differential Voltage Range
(IN+ – IN)
Absolute/Common Mode REF+ Voltage
Absolute/Common Mode REFVoltage
Reference Differential Voltage Range
(REF+ – REF)
IN+ Sampling Capacitance
INSampling Capacitance
REF+ Sampling Capacitance
REFSampling Capacitance
Leakage Current, Inputs and Reference
Average Input/Reference Current
During Sampling
MUX Break-Before-Make
MUX Off Isolation
CONDITIONS
CS = VCC, IN+ = GND, IN= GND,
REF+ = 5V, REF= GND
VIN = 2VP-P DC to 1.8MHz
MIN
GND – 0.3V
GND – 0.3V
–VREF/2
0.1
GND
0.1
–15
TYP MAX UNITS
VCC + 0.3V
VCC + 0.3V
VREF/2
V
V
V
VCC
VCC – 0.1V
VCC
V
V
V
2
2
2
2
1 15
pF
pF
pF
pF
nA
Varies, See Applications Section
nA
50 ns
120 dB
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LTC2444/LTC2445/
LTC2448/LTC2449
DIGITAL I PUTS A D DIGITAL OUTPUTS The denotes 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
VIH High Level Input Voltage
CS, FO
VIL Low Level Input Voltage
CS, FO
VIH High Level Input Voltage
SCK
4.5V VCC 5.5V
4.5V VCC 5.5V
4.5V VCC 5.5V (Note 8)
2.5
2.5
V
0.8 V
V
VIL Low Level Input Voltage
SCK
4.5V VCC 5.5V (Note 8)
0.8 V
IIN Digital Input Current
CS, FO, EXT, SOI
IIN Digital Input Current
SCK
0V VIN VCC
0V VIN VCC (Note 8)
–10
–10
10 µA
10 µA
CIN Digital Input Capacitance
CS, FO
CIN Digital Input Capacitance
SCK
(Note 8)
10 pF
10 pF
VOH High Level Output Voltage
SDO, BUSY
IO = –800µA
VCC – 0.5V
V
VOL Low Level Output Voltage
SDO, BUSY
IO = 1.6mA
0.4V V
VOH High Level Output Voltage
SCK
IO = –800µA (Note 9)
VCC – 0.5V
V
VOL Low Level Output Voltage
SCK
IO = 1.6mA (Note 9)
0.4V V
IOZ Hi-Z Output Leakage
SDO
–10
10 µA
POWER REQUIRE E TS The denotes 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
VCC Supply Voltage
4.5
5.5 V
ICC Supply Current
Conversion Mode
CS = 0V (Note 7)
8 11
Sleep Mode
CS = VCC (Note 7)
8 30
WU
TI I G CHARACTERISTICS The denotes specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 3)
mA
µA
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
fEOSC
tHEO
tLEO
tCONV
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time
OSR = 256 (SDI = 0)
OSR = 32768 (SDI = 1)
0.1
25
25
0.99
126
20
10000
10000
1.13 1.33
145 170
MHz
ns
ns
ms
ms
External Oscillator (Notes 10, 13)
40 • OSR +170
fEOSC (kHz)
ms
fISCK Internal SCK Frequency
Internal Oscillator (Note 9)
External Oscillator (Notes 9, 10)
0.8
0.9 1
fEOSC/10
MHz
Hz
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LTC2444/LTC2445/
LTC2448/LTC2449
TI I G CHARACTERISTICS The denotes 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
DISCK
Internal SCK Duty Cycle
(Note 9)
45
55 %
fESCK
tLESCK
External SCK Frequency Range
External SCK Low Period
(Note 8)
(Note 8)
25
20 MHz
ns
tHESCK
tDOUT_ISCK
External SCK High Period
Internal SCK 32-Bit Data Output Time
(Note 8)
Internal Oscillator (Notes 9, 11)
External Oscillator (Notes 9, 10)
25
41.6
35.3 30.9
320/fEOSC
ns
µs
s
tDOUT_ESCK
t1
t2
External SCK 32-Bit Data Output Time
CS to SDO Low Z
CS to SDO High Z
(Note 8)
(Note 12)
(Note 12)
32/fESCK
0
25
0
25
s
ns
ns
t3 CS to SCK
t4 CS to SCK
(Note 9)
(Notes 8, 12)
25
5
µs
ns
tKQMAX
tKQMIN
SCK to SDO Valid
SDO Hold After SCK
(Note 5)
15
25 ns
ns
t5 SCK Set-Up Before CS
t6 SCK Hold After CS
50
ns
50 ns
t7 SDI Setup Before SCK
t8 SDI Hold After SCK
(Note 5)
(Note 5)
10
10
ns
ns
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 = 4.5V to 5.5V unless otherwise specified.
VREF = REF+ – REF, VREFCM = (REF+ + REF)/2;
VIN = IN+ – IN, VINCM = (IN+ + IN)/2.
Note 4: FO pin tied to GND or to external conversion clock source with
fEOSC = 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 fESCK 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 CLOAD = 20pF.
Note 10: The external oscillator is connected to the FO pin. The external
oscillator frequency, fEOSC, is expressed in Hz.
Note 11: The converter uses the internal oscillator. FO = 0V.
Note 12: Guaranteed by design and test correlation.
Note 13: There is an internal reset that adds an additional 1µs (typ) to the
conversion time.
PI FU CTIO S
GND (Pins 1, 4, 5, 6, 31, 32, 33): Ground. Multiple
ground pins internally connected for optimum ground
current flow and VCC decoupling. Connect each one of
these pins to a common ground plane through a low
impedance connection. All 7 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 outputting/
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
indicating data is being output.
COM (Pin 7): The common negative input (IN) for all
single ended multiplexer configurations. The voltage on
CH0-CH15 and COM pins can have any value between
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