LTC1287
1
3V Single Chip 12-Bit
Data Acquisition System
s
Single Supply 3.3V or
±
3.3V Operation
s
Built-In Sample-and-Hold
s
Direct 3-Wire Interface to Most MPU Serial Ports and
All MPU Parallel Ports
s
30kHz Maximum Throughput Rate
S
FEATURE
The LTC1287 is a 3V data acquisition component which
contains a serial I/O successive approximation A/D con-
verter. The device specifications are guaranteed at a
supply voltage of 2.7V. It uses LTCMOS
TM
switched ca-
pacitor technology to perform a 12-bit unipolar, A/D
conversion. The differential input has an on-chip sample-
and-hold on the (+) input.
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 and received over
three wires. The low voltage operating capability and the
low power consumption of this device make it ideally
suited for battery applications. Given the ease of use, small
package size and the minimum number of interconnects
for I/O, the LTC1287 can be used for remote sensing
applications.
KEY SPECIFICATIO S
U
s
Minimum Guaranteed Supply Voltage: 2.7V
s
Resolution: 12 Bits
s
Fast Conversion Time: 24
µ
s Max Over Temp.
s
Low Supply Current: 1.0mA
U
A
O
PPLICATI
TYPICAL
s
Battery-Powered Instruments
s
Data Logger
s
Data Acquisition Modules
LTCMOS is a trademark of Linear Technology Corporation
D
U
ESCRIPTIO
V
CC
CLK
D
OUT
V
REF
LTC1287
CS
+IN
IN
GND
+
+
LT1004-1.2
10k
22
µ
F TANTALUM
22
µ
F
TANTALUM
+
DIFFERENTIAL INPUTS
COMMON MODE RANGE
0V TO V
CC
*
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
OTHER CHANNEL IS OVERVOLTAGED (V
IN
< GND OR V
IN
> V
CC
). SEE SECTION
ON OVERVOLTAGE PROTECTION IN THE APPLICATIONS INFORMATION.
*
3V
LITHIUM
TO AND FROM MPU
1287 TA01
3V Differential Input Data Acquisition System
INL with V
REF
= 1.2V
CODE
0
ERROR (LSB)
0.5
1.0
2048
LTC1287 TA02
0
1.0
512
1024
1536
0.5
2560
3072
3584
4096
2
LTC1287
W
U
U
PACKAGE/ORDER I FOR ATIO
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
(Notes 1 and 2)
Supply Voltage (V
CC
) to GND .................................. 12V
Voltage
Analog and Reference 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
LTC1287BI, LTC1287CI ................... 40
°
C TO 85
°
C
LTC1287BC, LTC1287CC ....................... 0
°
C to 70
°
C
Storage Temperature Range ................ 65
°
C to 150
°
C
Lead Temperature (Soldering, 10 sec.)................ 300
°
C
ORDER PART
NUMBER
LTC1287BIJ
LTC1287CIJ
LTC1287BIN
LTC1287CIN
LTC1287BCJ
LTC1287CCJ
LTC1287BCN
LTC1287CCN
1
2
3
4
5
6
7
8
TOP VIEW
J8 PACKAGE
8-LEAD CERAMIC DIP
V
CC
CLK
D
OUT
V
REF
CS
+IN
IN
GND
1287 PO
N8 PACKAGE
8-LEAD PLASTIC DIP
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
Offset Error
V
CC
= 2.7V (Note 4)
q
±
3.0
±
3.0
LSB
Linearity Error (INL)
V
CC
= 2.7V (Notes 4 & 5)
q
±
0.5
±
0.5
LSB
Gain Error
V
CC
= 2.7V (Note 4)
q
±
0.5
±
1.0
LSB
Minimum Resolution for Which No
q
12
12
Bits
Missing Codes are Guaranteed
Analog and REF Input Range
(Note 7)
V
On Channel Leakage Current (Note 8)
On Channel = 3V
q
±
1
±
1
µ
A
Off Channel = 0V
On Channel = 0V
q
±
1
±
1
µ
A
Off Channel = 3V
Off Channel Leakage Current (Note 8)
On Channel = 3V
q
±
1
±
1
µ
A
Off Channel = 0V
On Channel = 0V
q
±
1
±
1
µ
A
Off Channel = 3V
LTC1287B
LTC1287C
(Note 3)
CO VERTER A D ULTIPLEXER CHARACTERISTICS
U
U W
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
f
CLK
Clock Frequency
(Note 6)
(Note 9)
0.5
MHz
t
SMPL
Analog Input Sample Time
See Operating Sequence
1.5
CLK Cycles
t
CONV
Conversion Time
See Operating Sequence
12
CLK Cycles
t
CYC
Total Cycle Time
See Operating Sequence (Note 6)
14 CLK+
Cycles
5.0
µ
s
t
dDO
Delay Time, CLK
to D
OUT
Data Valid
See Test Circuits
q
250
450
ns
t
dis
Delay Time, CS
to D
OUT
Hi-Z
See Test Circuits
q
80
160
ns
t
en
Delay Time, CLK
to D
OUT
Enabled
See Test Circuits
q
130
250
ns
AC CHARACTERISTICS
(Note 3)
LTC1287B/LTC1287C
(V
) 0.05V to V
CC
+ 0.05V
LTC1287
3
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IH
High Level Input Voltage
V
CC
= 3.6V
q
2.1
V
V
IL
Low Level Input Voltage
V
CC
= 3.0V
q
0.45
V
I
IH
High Level Input Current
V
IN
= V
CC
q
2.5
µ
A
I
IL
Low Level Input Current
V
IN
= 0V
q
2.5
µ
A
V
OH
High Level Output Voltage
V
CC
= 3.0V, I
O
= 20
µ
A
2.90
V
I
O
= 400
µ
A
q
2.7
2.85
V
V
OL
Low Level Output Voltage
V
CC
= 3.0V, I
O
= 20
µ
A
0.05
V
I
O
= 400
µ
A
q
0.10
0.3
V
I
OZ
High Z Output Leakage
V
OUT
= V
CC
, CS High
q
3
µ
A
V
OUT
= 0V, CS High
q
3
µ
A
I
SOURCE
Output Source Current
V
OUT
= 0V
10
mA
I
SINK
Output Sink Current
V
OUT
= V
CC
9
mA
I
CC
Positive Supply Current
CS High
q
1.5
5
mA
I
REF
Reference Current
V
REF
= 2.5V
q
10
50
µ
A
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t
hDO
Time Output Data Remains Valid After CLK
50
ns
t
f
D
OUT
Fall Time
See Test Circuits
q
40
100
ns
t
r
D
OUT
Rise Time
See Test Circuits
q
40
100
ns
t
WHCLK
CLK High Time
V
CC
= 3V (Note 6)
600
ns
t
WLCLK
CLK Low Time
V
CC
= 3V (Note 6)
800
ns
t
suCS
Setup Time, CS
Before CLK
V
CC
= 3V (Note 6)
100
ns
t
WHCS
CS High Time Between Data Transfer Cycles
V
CC
= 3V (Note 6)
5.0
µ
s
t
WLCS
CS Low Time During Data Transfer
V
CC
= 3V (Note 6)
14
CLK Cycles
C
IN
Input Capacitance
Analog Inputs On Channel
100
pF
Analog Inputs Off Channel
5
pF
Digital Inputs
5
pF
AC CHARACTERISTICS
LTC1287B/LTC1287C
ELECTRICAL C
C
HARA TER STICS
DIGITAL A D
U
I
DC
(Note 3)
(Note 3)
The
q
denotes specifications which apply over the operating temperature
range; all other limits and typicals T
A
= 25
°
C.
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
= 3V, V
REF
= 2.5V, CLK = 500kHz unless otherwise specified.
Note 4: One LSB is equal to V
REF
divided by 4096. For example, when V
REF
= 2.5V, 1LSB = 2.5V/4096 = 0.61mV.
Note 5: Integral nonlinearity error 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.
LTC1287B/LTC1287C
Note 6: Recommended operating conditions.
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, as high level analog
inputs 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
30kHz at 85
°
C and
f
CLK
3kHz at 25
°
C.
4
LTC1287
REFERENCE VOLTAGE (V)
0
0
CHANGE IN LINEARITY (LSB = 1/4096
×
V
REF
)
0.1
0.2
0.3
0.4
0.5
0.5
1.0
1.5
2.0
LTC1287 G4
2.5
3.0
V
CC
= 3V
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Supply Current vs Supply Voltage
Change in Linearity vs Reference
Voltage
Change in Gain vs Temperature
D
OUT
Delay Time vs Temperature
Change in Offset vs Temperature
Change in Gain vs Reference
Voltage
REFERENCE VOLTAGE (V)
0
0.5
CHANGE IN GAIN (LSB = 1/4096
×
V
REF
)
0.4
0.3
0.2
0.1
0
0.5
1.0
1.5
2.0
LTC1287 G5
2.5
3.0
V
CC
= 3V
Supply Current vs Temperature
REFERENCE VOLTAGE (V)
0
0
OFFSET (LSB = 1/4096
×
V
REF
)
0.1
0.3
0.4
0.5
2.0
0.9
LTC1287 G3
0.2
1.0
3.0
0.6
0.7
0.8
0.5
1.5
2.5
V
CC
= 3V
V
OS
= 0.250mV
V
OS
= 0.125mV
Unadjusted Offset Voltage vs
Reference Voltage
AMBIENT TEMPERATURE (°C)
40
0
MAGNITUDE OF OFFSET CHANGE (LSB)
0.2
0.5
0
40
60
LTC1287 G6
0.1
0.4
0.3
20
20
80
100
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
Change in Linearity vs
Temperature
AMBIENT TEMPERATURE (°C)
40
0
MAGNITUDE OF LINEARITY CHANGE (LSB)
0.2
0.5
0
40
60
LTC1287 G7
0.1
0.4
0.3
20
20
80
100
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
AMBIENT TEMPERATURE (°C)
40
200
250
350
20
60
LTC1287 G9
150
100
20
0
40
80
100
50
0
300
D
OUT
DELAY TIME FROM CLK
(ns)
V
CC
= 3V
MSB-FIRST DATA
LSB-FIRST DATA
SUPPLY VOLTAGE (V)
2.7
0.8
SUPPLY CURRENT (mA)
1.0
1.4
1.6
1.8
2.8
2.2
2.9
3.1 3.2
3.6
LTC1287 G1
1.2
2.4
2.6
2.0
2.8
3.0
3.3 3.4 3.5
CLK = 500kHz
T
A
= 25°C
TEMPERATURE (°C)
40
1.3
SUPPLY CURRENT (mA)
1.4
1.6
1.7
1.8
10
20
35
95
LTC1287 G2
1.5
25
5
50
65
80
1.9
CLK = 500kHz
V
CC
= 3V
AMBIENT TEMPERATURE (°C)
40
0
MAGNITUDE OF GAIN CHANGE (LSB)
0.2
0.5
0
40
60
LTC1287 G8
0.1
0.4
0.3
20
20
80
100
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
LTC1287
5
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
R
SOURCE
(
)
100
0
MAXIMUM CLK FREQUENCY* (MHz)
300
400
500
1k
10k
100k
LTC G10
200
100
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
+IN
IN
+V
IN
R
SOURCE
R
SOURCE
+ (
)
100
1k
10k
LTC1287 G13
1
S & H ACQUISITION TIME TO 0.02% (
µ
s)
10
100
+
V
IN
R
SOURCE
+
V
REF
= 2.5V
V
CC
= 3V
T
A
= 25°C
0V TO 2.5V INPUT STEP
Sample-and-Hold Acquisition
Time vs Source Resistance
AMBIENT TEMPERATURE (°C)
50
0
INPUT CHANNEL LEAKAGE CURRENT (nA)
100
300
400
500
1000
700
10
30
50
130
LTC1287 G14
200
800
900
600
30
10
70
90 110
ON CHANNEL
OFF CHANNEL
GUARANTEED
Input Channel Leakage Current vs
Temperature
REFERENCE VOLTAGE (V)
0
0
PEAK-TO-PEAK NOISE ERROR (LSB)
0.2
0.3
0.4
0.5
0.6
0.7
0.5
1.0
1.5
2.0
LTC1287 G15
2.5
0.8
0.9
1.0
0.1
3.0
LTC1287 NOISE = 200
µ
V
P-P
Noise Error vs Reference Voltage
Maximum Clock Rate vs Source
Resistance
Minimum Clock Rate for 0.1LSB
Error**
Maximum Filter Resistor vs Cycle
Time
*** MAXIMUM R
FILTER
REPRESENTS THE FILTER RESISTOR VALUE AT WHICH A 0.1LSB
CHANGE IN FULL SCALE ERROR FROM ITS VALUE AT R
FILTER
= 0
IS FIRST
DETECTED.
*
MAXIMUM CLK FREQUENCY REPRESENTS THE CLK FREQUENCY AT WHICH A 0.1LSB
SHIFT IN THE ERROR AT ANY CODE TRANSITION FROM ITS 500kHz VALUE IS FIRST
DETECTED.
**
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 500kHz VALUE IS FIRST DETECTED.
#
PIN
FUNCTION
DESCRIPTION
1
CS
Chip Select Input
A logic low on this input enables the LTC1287.
2, 3
+IN, IN
Analog Inputs
These inputs must be free of noise with respect to GND.
4
GND
Analog Ground
GND should be tied directly to an analog ground plane.
5
V
REF
Reference Input
The reference input defines the span of the A/D converter and must be kept free of noise with respect to GND.
6
D
OUT
Digital Data Output
The A/D conversion result is shifted out of this output.
7
CLK
Shift Clock
This clock synchronizes the serial data transfer.
8
V
CC
Positive Supply
This supply must be kept free of noise and ripple by bypassing directly to the analog ground plane.
PI FU CTIO S
U
U
U
CYCLE TIME (
µ
s)
10
MAXIMUM R
FILTER
*** (
)
100
1k
10k
10
1000
10000
LTC1287 G12
1
100
+
V
IN
C
FILTER
1
µ
F
R
FILTER
AMBIENT TEMPERATURE (°C)
50
MINIMUM CLK FREQUENCY (MHz) 0.05
0.10
0.15
0.20
25
0
25
50
LTC1287 G11
75
100
0.25
V
CC
= 3V
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