multiplexed ratiometric measurements. Four sets of se-
lectable differential inputs coupled with four sets of differ-
ential reference inputs allow multiple RTDs, bridges 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 (ther-
mocouples, voltages, current sense, etc.). The flexible
input multiplexer allows single-ended or differential in-
puts 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 2x mode
can be selected for any speed-enabling output rates up to
8kHz with one cycle of latency.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Protected by U.S. Patents, including 6140950, 6169506, 6208279, 6411242, 6639526
■
■
■
■
■
■
■
■
■
Five Selectable Differential Reference Inputs
Four Differential/Eight Single-Ended Inputs
4-Way MUX for Multiple Ratiometric
Measurements
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
LTC2447 Includes MUXOUT/ADCIN for External
Buffering or Gain
Tiny QFN 5mm x 7mm Package
APPLICATIO S
■
■
■
■
■
Flow
Weight Scales
Pressure
Direct Temperature Measurement
Gas Chromatography
TYPICAL APPLICATIO
V
CC
REF
+
IN
+
•
•
•
19-INPUT
4-OUTPUT
MUX
LTC2446 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)
Multiple Ratiometric Measurement System
LTC2446
CS
+
–
IN
–
REF
–
VARIABLE SPEED/
RESOLUTION 24-BIT
∆Σ
ADC
SDI
SDO
SCK
RMS NOISE (µV)
10
1
0.1
1
24467 TA01
24467 TA02
U
U
U
1000
10
100
CONVERSION RATE (Hz)
10000
24467fa
1
LTC2446/LTC2447
ABSOLUTE
AXI U RATI GS
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)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND
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
CH0 8
CH1 9
V
REF01–
10
V
REF01+
11
CH2 12
13 14 15 16 17 18 19
39
31 GND
30 REFG
–
38 37 36 35 34 33 32
GND 1
BUSY 2
EXT 3
GND 4
GND 5
GND 6
COM 7
CH0 8
+
GND
31 GND
30 REFG
–
29 REFG
+
28 V
CC
27 MUXOUTN
26 ADCINN
25 ADCINP
24 MUXOUTP
23 V
REF67+
22 V
REF67–
21 CH7
20 CH6
SDO
SCK
29 REFG
+
28 V
CC
27 NC
26 NC
25 NC
24 NC
23 V
REF67
21 CH7
20 CH6
22 V
REF67–
39
CH1 9
V
REF01–
10
V
REF01+
11
CH2 12
13 14 15 16 17 18 19
V
REF23_
V
REF23+
V
REF45–
V
REF45+
CH3
CH4
CH5
V
REF23–
V
REF23+
V
REF45–
V
REF45+
CH3
CH4
CH5
UHF PACKAGE
38-LEAD (5mm
×
7mm) PLASTIC QFN
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
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS GND
MUST BE SOLDERED TO PCB
ORDER PART
NUMBER
LTC2446CUHF
LTC2446IUHF
QFN PART
MARKING*
2446
ORDER PART
NUMBER
LTC2447CUHF
LTC2447IUHF
SDI
CS
F
O
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.
2
U
U
W
W W
U
W
(Notes 1, 2)
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
TOP VIEW
QFN PART
MARKING*
2447
24467fa
LTC2446/LTC2447
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
+
= 0.75REF
+
, 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
●
●
●
●
●
●
●
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
24467fa
3
LTC2446/LTC2447
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
OSR = 32768
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
24467fa
LTC2446/LTC2447
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 Setup Before CS
↓
SCK Hold After CS
↓
SDI Setup 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; 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.
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 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 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-CH7 and COM pins can have any value between GND
24467fa
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
