LTC1291
Single Chip 12-Bit
Data Acquisition System
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
Built-In Sample-and-Hold
Single Supply 5V Operation
Power Shutdown
Direct 3- or 4-Wire Interface to Most MPU Serial
Ports and All MPU Parallel Ports
Two-Channel Analog Multiplexer
Analog Inputs Common Mode to Supply Rails
8-Pin DIP Package
KEY SPECIFICATIO S
s
s
s
The LTC
®
1291 is a data acquisition system that contains
a serial I/O successive approximation A/D converter. It
uses LTCMOS
TM
switched capacitor technology to per-
form a 12-bit unipolar A/D conversion. The input multi-
plexer can be configured for either single-ended or differ-
ential inputs. An on-chip sample-and-hold is included on
the “+” input. When the LTC1291 is idle, it can be powered
down in applications where low power consumption is
desired. An external reference is not required because the
LTC1291 takes its reference from the power supply (V
CC
).
All these features are packaged in an 8-pin DIP.
The serial I/O is designed to communicate without external
hardware to most MPU serial ports and all MPU parallel
I/O ports allowing data to be transmitted over three or four
wires. Given the accuracy, ease of use and small package
size, this device is well suited for digitizing analog signals
in remote applications where minimum number of inter-
connects, small physical size, and low power consump-
tion are important.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS
TM
is a trademark of Linear Technology Corporation
Resolution: 12 Bits
Fast Conversion Time: 12µs Max Over Temp.
Low Supply Current:
6.0mA (Typ) Active Mode
10µA (Max) Shutdown Mode
TYPICAL APPLICATIO
2-Channel 12-Bit Data Acquisition System
22µF
TANTALUM
5V
0.5
0.4
0.3
CS
CH0
2-CHANNEL
MUX*
CH1
GND
V
CC
(V
REF
)
0.1µF
CLK
LTC1291
D
OUT
D
IN
DO
DELTA (LSB)
SCK
MC68HC11
MISO
MOSI
1291 TA01
*FOR OVERVOLTAGE PROTECTION, LIMIT THE INPUT CURRENT TO 15mA
PER PIN OR CLAMP THE INPUTS TO V
CC
AND GND WITH 1N4148 DIODES.
CONVERSION RESULTS ARE NOT VALID WHEN THE SELECTED CHANNEL OR
THE OTHER CHANNEL IS OVERVOLTAGED (V
IN
< GND OR V
IN
> V
CC
). SEE
SECTION ON OVERVOLTAGE PROTECTION IN THE APPLICATIONS INFORMATION.
U
Channel-to-Channel
INL Matching
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
0
512 1024 1536 2048 2560 3072 3584 4096
CODE
1291 TA02
U
U
+
1291fa
1
LTC1291
ABSOLUTE
(Notes 1 and 2)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CS 1
CH0 2
CH1 3
GND 4
8
7
6
5
V
CC
(V
REF
)
CLK
D
OUT
D
IN
Supply Voltage (V
CC
) to GND .................................. 12V
Voltage
Analog Inputs ............................ –0.3V to V
CC
+ 0.3V
Digital Inputs ........................................ –0.3V to 12V
Digital Outputs .......................... –0.3V to V
CC
+ 0.3V
Power Dissipation ............................................. 500mW
Operating Temperature Range
LTC1291BC, LTC1291CC,
LTC1291DC ............................................ 0°C to 70°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC1291BCN8
LTC1291CCN8
LTC1291DCN8
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 100°C,
θ
JA
= 130°C/ W (N8)
J8 PACKAGE
8-LEAD CERAMIC DIP
T
JMAX
= 150°C,
θ
JA
= 100°C/ W (J8)
LTC1291BCJ8
LTC1291CCJ8
LTC1291DCJ8
OBSOLETE PACKAGE
Consider N8 Package for Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
CO VERTER A D
PARAMETER
Offset Error
Linearity Error (INL)
Gain Error
Minimum Resolution for which No
Missing Codes are Guaranteed
Analog Input Range
On Channel Leakage Current
(Note 8)
The
q
denotes the specifications
which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
LTC1291B
CONDITIONS
(Note 4)
(Note 4 & 5)
(Note 4)
q
q
q
q
ULTIPLEXER CHARACTERISTICS
MIN
TYP
MAX
±3.0
±0.5
±1.0
12
MIN
TYP
LTC1291C
MAX
±3.0
±0.5
±2.0
12
– 0.05V to V
CC
+ 0.05V
±1
±1
±1
±1
LTC1291D
MIN
TYP
MAX
±3.0
±0.75
±4.0
12
UNITS
LSB
LSB
LSB
Bits
V
±1
±1
±1
±1
µA
µA
µA
µA
(Note 7)
On Channel = 5V
Off Channel = 0V
On Channel = 0V
Off Channel = 5V
q
q
q
q
±1
±1
±1
±1
Off Channel Lekage Current
(Note 8)
On Channel = 5V
Off Channel = 0V
On Channel = 0V
Off Channel = 5V
The
q
denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
f
CLK
t
SMPL
t
CONV
t
CYC
t
dDO
PARAMETER
Clock Frequency
Analog Input Sample Time
Conversion Time
Total Cycle Time
Delay Time, CLK↓ to D
OUT
Data Valid
CONDITIONS
V
CC
= 5V (Note 6)
See Operating Sequence
See Operating Sequence
See Operating Sequence (Note 6)
See Test Circuits
q
AC CHARACTERISTICS
LTC1291B/LTC1291C/LTC1291D
MIN
TYP
MAX
(Note 9)
2.5
12
18 CLK
+ 500ns
160
300
1.0
UNITS
MHz
CLK Cycles
CLK Cycles
Cycles
ns
1291fa
2
U
W
U
U
W W
W U
W
U
LTC1291
AC CHARACTERISTICS
SYMBOL
t
dis
t
en
t
hDI
t
hDO
t
WHCLK
t
WLCLK
t
f
t
r
t
suDI
t
suCS
t
WHCS
t
WLCS
C
IN
PARAMETER
Delay Time, CS↑ to D
OUT
Hi-Z
Delay Time, CLK↓ to D
OUT
Enabled
Hold Time, D
IN
after CLK↑
Time Output Data Remains Valid after CLK↓
CLK High Time
CLK Low Time
D
OUT
Fall Time
D
OUT
Rise Time
Setup Time, D
IN
Stable before CLK↑
Setup Time, CS↓ before CLK↑
CS High Time During Conversion
CS Low Time During Data Transfer
Input Capacitance
V
CC
= 5V (Note 6)
V
CC
= 5V (Note 6)
See Test Circuits
See Test Circuits
V
CC
= 5V (Note 6)
V
CC
= 5V (Note 6)
V
CC
= 5V (Note 6)
V
CC
= 5V (Note 6)
Analog Inputs On Channel
Analog Inputs Off Channel
Digital Inputs
q
q
The
q
denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
See Test Circuits
See Test Circuits
V
CC
= 5V (Note 6)
q
q
LTC1291B/LTC1291C/LTC1291D
MIN
TYP
MAX
80
80
50
130
300
400
65
25
50
50
500
18
100
5
5
130
50
150
200
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
CLK Cycles
pF
pF
pF
DIGITAL A D DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
IH
V
IL
I
IH
I
IL
V
OH
V
OL
I
OZ
I
SOURCE
I
SINK
I
CC
PARAMETER
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
High Level Output Voltage
Low Level Output Voltage
High Z Output Leakage
Output Source Current
Output Sink Current
Positive Supply Current
CONDITIONS
V
CC
= 5.25V
V
CC
= 4.75V
V
IN
= V
CC
V
IN
= 0V
V
CC
= 4.75V, I
OUT
= –10µA
V
CC
= 4.75V, I
OUT
= – 360µA
V
CC
= 4.75V, I
OUT
= 1.6mA
V
OUT
= V
CC
, CS High
V
OUT
= 0V, CS High
V
OUT
= 0V
V
OUT
= V
CC
CS High
CS High Power Shutdown CLK Off
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
All voltage values are with respect to ground (unless otherwise
noted).
Note 3:
V
CC
= 5V, CLK = 1.0MHz unless otherwise specified.
Note 4:
One LSB is equal to V
CC
divided by 4096. For example, when V
CC
=
5V, 1LSB = 5V/4096 = 1.22mV.
Note 5:
Linearity error is specified between the actual end points of the
A/D transfer curve. The deviation is measured from the center of the
quantization band.
Note 6:
Recommended operating conditions.
The
q
denotes the specifications which
apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
LTC1291B/LTC1291C/LTC1291D
MIN
TYP
MAX
q
q
q
q
q
q
q
q
U
UNITS
V
V
µA
µA
V
V
2.0
0.8
2.5
–2.5
2.4
4.7
4.0
0.4
3
–3
– 20
20
V
µA
µA
mA
mA
q
q
6
5
12
10
mA
µA
Note 7:
Two on-chip diodes are tied to each analog input which will
conduct for analog voltages one diode drop below GND or one diode drop
above V
CC
. Be careful during testing at low V
CC
levels (4.5V), as high level
analog inputs (5V) can cause this input diode to conduct, especially at
elevated temperature, and cause errors for inputs near full scale. This spec
allows 50mV forward bias of either diode. This means that as long as the
analog input does not exceed the supply voltage by more than 50mV, the
output code will be correct.
Note 8:
Channel leakage current is measured after the channel selection.
Note 9:
Increased leakage currents at elevated temperatures cause the
S/H to droop, therefore it is recommended that f
CLK
≥
125kHz at 125°C,
f
CLK
≥
30kHz at 85°C and f
CLK
≥
3kHz at 25°C.
1291fa
3
LTC1291
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
10
CLK = 1MHz
T
A
= 25°C
8
SUPPLY CURRENT (mA)
9
SUPPLY CURRENT (mA)
8
7
6
5
4
CLK = 1MHz
V
CC
= 5V
CHANGE IN OFFSET (LSB = 1/4096 • V
CC
(V
REF
))
6
4
2
0
4
5
SUPPLY VOLTAGE (V)
CHANGE IN GAIN ERROR (LSB = 1/4096
×
V
CC
(V
REF
))
Change in Linearity vs Supply
Voltage
CHANGE IN LINEARITY (LSB = 1/4096 • V
CC
(V
REF
))
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
4.0
4.5
5.5
5.0
SUPPLY VOLTAGE (V)
6.0
1291 G05
MAGNITUDE OF OFFSET CHANGE (LSB)
0.4
0.3
0.2
0.1
0
4.0
4.5
5.5
5.0
SUPPLY VOLTAGE (V)
Change in Linearity vs
Temperature
0.5
MAGNITUDE OF LINEARITY CHANGE (LSB)
MAGNITUDE OF GAIN CHANGE (LSB)
MINIMUM CLK FREQUENCY* (MHz)
V
CC
= 5V
CLK = 1MHz
0.4
0.3
0.2
0.1
0
50
25
0
75 100
–50 –25
AMBIENT TEMPERATURE (°C)
* AS THE CLK FREQUENCY IS DECREASED FROM 1MHz, MINIMUM CLK FREQUENCY (∆ERROR
≤
0.1LSB) REPRESENTS THE
FREQUENCY AT WHICH A 0.1LSB SHIFT IN ANY CODE TRANSITION FROM ITS 1MHz VALUE IS FIRST DETECTED
1291fa
4
U W
6
1291 G01
Supply Current vs Temperature
10
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
Change in Offset vs Supply
Voltage
3
–50 –30 –10 10 30 50 70 90 110 130
AMBIENT TEMPERATURE (°C)
1291 G02
–0.5
4.0
4.5
5.5
5.0
SUPPLY VOLTAGE (V)
6.0
1291 G03
Change in Gain Error vs Supply
Voltage
0.5
Change in Offset vs Temperature
0.5
V
CC
= 5V
CLK = 1MHz
0.4
0.3
0.2
0.1
6.0
1291 G04
0
50
25
0
75 100
–50 –25
AMBIENT TEMPERATURE (°C)
125
1291 G06
Change in Gain vs Temperature
0.5
V
CC
= 5V
CLK = 1MHz
0.4
Minimum Clock Rate for
0.1 LSB Error
V
CC
= 5V
0.25
0.20
0.15
0.10
0.05
0.3
0.2
0.1
125
0
50
25
0
75 100
–50 –25
AMBIENT TEMPERATURE (°C)
125
–50
–25
25
50
75 100
0
AMBIENT TEMPERATURE (°C)
125
1291 G07
1291 G08
1291 G09
LTC1291
TYPICAL PERFOR A CE CHARACTERISTICS
D
OUT
Delay Time vs Temperature
250
V
CC
= 5V
MAXIMUM CLK FREQUENCY* (MHz)
1.0
D
OUT
DELAY TIME FROM CLK↓ (ns)
200
MAXIMUM R
FILTER
** (Ω)
150
MSB-FIRST DATA
100
LSB-FIRST DATA
50
0
–50
–25
25
50
75 100
0
AMBIENT TEMPERATURE (°C)
Sample-and-Hold Acquisition
Time vs Source Resistance
100
S/H AQUISITION TIME TO 0.02% (µs)
1000
INPUT CHANNEL LEAKAGE CURRENT (nA)
V
CC
= 5V
T
A
= 25°C
0V TO 5V INPUT STEP
10
V
IN
R
SOURCE
+
+
–
1
100
1k
R
SOURCE
+ (Ω)
PI FU CTIO S
CS (Pin 1):
Chip Select Input. A logic low on this input
enables the LTC1291.
CH0, CH1 (Pins 2, 3):
Analog Inputs. These inputs must
be free of noise with respect to GND.
GND (Pin 4):
Analog Ground. GND should be tied directly
to an analog ground plane.
D
IN
(Pin 5):
Digital Data Input. The multiplexer address is
shifted into this input.
U W
1291 G10
Maximum Clock Rate vs Source
Resistance
V
CC
= 5V
CLK = 1MHz
Maximum Filter Resistor vs
Cycle Time
10k
R
FILTER
0.8
1k
+V
IN
C
FILTER
≥1µF
+
–
0.6
+V
IN
R
SOURCE
–
+
+IN
–
–IN
100
0.4
0.2
10
125
0
100
1k
10k
R
SOURCE –
(Ω)
100k
1291 G11
1
10
100
1k
CYCLE TIME (µs)
10k
1291 G12
Input Channel Leakage Current
vs Temperature
900
800
700
600
500
400
300
200
100
ON CHANNEL
OFF CHANNEL
GUARANTEED
* MAXIMUM CLK FREQUENCY REPRESENTS THE CLK
FREQUENCY AT WHICH A 0.1LSB SHIFT IN THE
ERROR AT ANY CODE TRANSITION FROM ITS 1MHz
VALUE IS FIRST DETECTED
**MAXIMUM R
FILTER
REPRESENTS THE FILTER RESISTOR
VALUE AT WHICH A 0.1LSB CHANGE IN FULL SCALE
ERROR FROM ITS VALUE AT R
FILTER
= 0Ω IS FIRST
DETECTED
10k
1291 G13
0
–50 –30 –10 10 30 50 70 90 110 130
AMBIENT TEMPERATURE (°C)
1291 G14
U
U
U
D
OUT
(Pin 6):
Digital Data Output. The A/D conversion
result is shifted out of this output.
CLK (Pin 7):
Shift Clock. This clock synchronizes the serial
data transfer.
V
CC
(V
REF
) (Pin 8):
Positive Supply and Reference Voltage.
This pin provides power and defines the span of the A/D
converter. This supply must be kept free of noise and
ripple by bypassing directly to the analog ground plane.
1291fa
5
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