channel (4-/8-differential) high speed 24-bit No Latency
∆Σ
TM
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/280nV
RMS
to 3.5kHz/25µV
RMS
(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 V
CC
, independent of V
REF
. 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.
Up to 8 Differential or 16 Single-Ended Input
Channels
Up to 8kHz Output Rate
Up to 4kHz Multiplexing Rate
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
LTC2445/LTC2449 Include MUXOUT/ADCIN for
External Buffering or Gain
Tiny QFN 5mm x 7mm Package
APPLICATIO S
■
■
■
■
■
High Speed Multiplexing
Weight Scales
Auto Ranging 6-Digit DVMs
Direct Temperature Measurement
High Speed Data Acquisition
TYPICAL APPLICATIO
Simple 24-Bit Variable Speed Data Acquisition System
4.5V TO 5.5V
1µF
CH0
CH1
•
•
•
CH7
CH8
•
•
•
CH15
COM
REF
–
GND
LTC2448
2444 TA01
REF
+
V
CC
F
O
RMS NOISE (µV)
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
(SIMULTANEOUS 50Hz/60Hz
REJECTION AT 6.9Hz OUTPUT RATE)
4-WIRE
SPI INTERFACE
THERMOCOUPLE
16-CHANNEL
MUX
+
–
VARIABLE SPEED/
RESOLUTION
DIFFERENTIAL
24-BIT
∆Σ
ADC
SDI
SCK
SDO
CS
U
U
U
LTC2444/LTC2448
Speed vs RMS Noise
100
V
CC
= 5V
V
REF
= 5V
V
IN+
= V
IN–
= 0V
2X SPEED MODE
NO LATENCY MODE
2.8µV AT 880Hz
280nV AT 6.9Hz
(50/60Hz REJECTION)
10
1
0.1
1
1000
10
100
CONVERSION RATE (Hz)
10000
2440 TA02
2444589fb
1
LTC2444/LTC2445/
LTC2448/LTC2449
ABSOLUTE
(Notes 1, 2)
AXI U RATI GS
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 150°C
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)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND
GND
SDO
SCK
SDI
CS
F
O
38 37 36 35 34 33 32
GND 1
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
NC 8
CH0 9
CH1 10
NC 11
NC 12
13 14 15 16 17 18 19
NC
NC
CH2
CH3
CH4
CH5
NC
ORDER PART
NUMBER
31 GND
30 REF
–
29 REF
+
28 V
CC
27 NC
GND 1
GND
38 37 36 35 34 33 32
31 GND
30 REF
–
29 REF
+
28 V
CC
27 MUXOUTN
39
26 ADCINN
25 ADCINP
24 MUXOUTP
23 NC
22 CH7
21 CH6
20 NC
13 14 15 16 17 18 19
CH2
CH3
NC
NC
CH4
CH5
NC
GND
SDO
SCK
SDI
CS
F
O
LTC2444CUHF
LTC2444IUHF
39
26 NC
25 NC
24 NC
23 NC
22 CH7
21 CH6
20 NC
QFN PART MARKING*
2444
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS GND
MUST BE SOLDERED TO PCB
TOP VIEW
GND
GND
SDO
SCK
SDI
CS
UHF PACKAGE
38-LEAD (5mm
×
7mm) PLASTIC QFN
GND
F
O
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
CH2
10
CH3
11
CH4
12
31 GND
30 REF
29 REF
28 V
CC
27 NC
–
+
ORDER PART
NUMBER
LTC2448CUHF
LTC2448IUHF
GND
SDO
SCK
SDI
CS
F
O
39
26 NC
25 NC
24 NC
23
CH15
22
CH14
21
CH13
20
CH12
QFN PART MARKING*
2448
13
14
15
16
17
18
19
CH10
CH11
CH5
CH6
CH7
CH8
CH9
CH10
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
UHF PACKAGE
38-LEAD (5mm
×
7mm) PLASTIC QFN
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/
*The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges.
2444589fb
2
CH11
CH5
CH6
CH7
CH8
CH9
U
U
W
W W
U
W
TOP VIEW
ORDER PART
NUMBER
LTC2445CUHF
LTC2445IUHF
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
NC 8
CH0 9
CH1 10
NC 11
NC 12
QFN PART MARKING*
2445
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
TOP VIEW
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
CH2
10
CH3
11
CH4
12
13
14
15
16
17
18
19
31 GND
30 REF
–
29 REF
+
28 V
CC
27 MUXOUTN
39
26 ADCINN
25 ADCINP
24 MUXOUTP
ORDER PART
NUMBER
LTC2449CUHF
LTC2449IUHF
23
CH15
22
CH14
21
CH13
20
CH12
QFN PART MARKING*
2449
LTC2444/LTC2445/
LTC2448/LTC2449
The
●
denotes 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
+
= 0.75 • REF
+
, 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
●
●
●
●
●
●
●
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
UNITS
Bits
ppm of V
REF
ppm of V
REF
µV
nV/°C
50
50
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
A ALOG I PUT A D REFERE CE
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
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–)
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
MUX Break-Before-Make
MUX Off Isolation
I
SAMPLE(IN+, IN–,
REF+, REF–)
t
OPEN
QIRR
U
U
U
U
CONDITIONS
●
●
●
●
●
●
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
CS = V
CC
, IN
+
= GND, IN
–
REF
+
= 5V, REF
–
= GND
= GND,
●
–15
1
15
nA
nA
ns
dB
Varies, See Applications Section
50
V
IN
= 2V
P-P
DC to 1.8MHz
120
2444589fb
3
LTC2444/LTC2445/
LTC2448/LTC2449
DIGITAL I PUTS A D 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
CS, F
O
Low Level Input Voltage
CS, F
O
High Level Input Voltage
SCK
Low Level Input Voltage
SCK
Digital Input Current
CS, F
O
, EXT, SOI
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)
●
●
●
●
●
The
●
denotes specifications which apply over the full
operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
4.5V
≤
V
CC
≤
5.5V
4.5V
≤
V
CC
≤
5.5V
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)
●
●
●
●
●
●
POWER REQUIRE E TS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
Conversion Mode
Sleep Mode
The
●
denotes specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
●
TI I G CHARACTERISTICS
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV
PARAMETER
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time
The
●
denotes specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
●
●
●
f
ISCK
Internal SCK Frequency
4
U W
U
U
MIN
2.5
TYP
MAX
UNITS
V
0.8
2.5
0.8
–10
–10
10
10
V
CC
– 0.5V
0.4V
V
CC
– 0.5V
0.4V
–10
10
10
10
V
V
V
µA
µA
pF
pF
V
V
V
V
µA
MIN
4.5
TYP
MAX
5.5
UNITS
V
mA
µA
CS = 0V (Note 7)
CS = V
CC
(Note 7)
●
●
8
8
11
30
UW
MIN
0.1
25
25
0.99
126
TYP
MAX
20
10000
10000
UNITS
MHz
ns
ns
ms
ms
ms
OSR = 256 (SDI = 0)
OSR = 32768 (SDI = 1)
External Oscillator (Notes 10, 13)
Internal Oscillator (Note 9)
External Oscillator (Notes 9, 10)
●
●
●
●
1.13
145
40 • OSR +170
f
EOSC
(kHz)
1.33
170
0.8
0.9
f
EOSC
/10
1
MHz
Hz
2444589fb
LTC2444/LTC2445/
LTC2448/LTC2449
TI I G CHARACTERISTICS
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 Set-Up Before CS
↓
SCK Hold After CS
↓
SDI Set-Up Before SCK
↑
SDI Hold After SCK
↑
The
●
denotes specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
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)
(Note 5)
●
●
●
●
●
●
●
●
●
●
●
●
●
●
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:
V
CC
= 4.5V 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.
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 V
CC
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
2444589fb
U
U
UW
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 5)
(Note 5)
●
●
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 1µs (typ) to the
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