LTC1287
3V Single Chip 12-Bit
Data Acquisition System
FEATURES
s
s
s
DESCRIPTIO
s
Single Supply 3.3V Operation
Built-In Sample-and-Hold
Direct 3-Wire Interface to Most MPU Serial Ports and
All MPU Parallel Ports
30kHz Maximum Throughput Rate
KEY SPECIFICATIO S
s
s
s
s
The LTC
®
1287 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS is a trademark of Linear Technology Corporation
Minimum Guaranteed Supply Voltage: 2.7V
Resolution: 12 Bits
Fast Conversion Time: 24µs Max Over Temp.
Low Supply Current: 1.0mA
APPLICATIO S
s
s
s
Battery-Powered Instruments
Data Logger
Data Acquisition Modules
TYPICAL APPLICATIO
3V Differential Input Data Acquisition System
22µF TANTALUM
+
CS
DIFFERENTIAL INPUTS
COMMON MODE RANGE
0V TO V
CC
*
V
CC
10k
CLK
LTC1287
1.0
3V
LITHIUM
+
–
+IN
–IN
GND
0.5
ERROR (LSB)
D
OUT
V
REF
22µF
TANTALUM
0
+
LT1004-1.2
–0.5
TO AND FROM MPU
* 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.
–1.0
0
512
1024
1536
2048
CODE
LTC1287 TA02
1287 TA01
U
INL with V
REF
= 1.2V
2560
3072
3584
4096
1287fa
U
U
U
1
LTC1287
ABSOLUTE
(Notes 1 and 2)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CS 1
+IN 2
–IN 3
GND 4
8 V
CC
7 CLK
6 D
OUT
5 V
REF
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 .................... 0°C to 70°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
ORDER PART
NUMBER
LTC1287BCN8
LTC1287CCN8
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 100°C,
θ
JA
= 130°C/W (N)
J8 PACKAGE
8-LEAD CERAMIC DIP
T
JMAX
= 150°C,
θ
JA
= 100°C/W (J)
LTC1287BCJ8
LTC1287CCJ8
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 and REF 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)
CONDITIONS
V
CC
= 2.7V (Note 4)
V
CC
= 2.7V (Notes 4 & 5)
V
CC
= 2.7V (Note 4)
q
q
q
q
ULTIPLEXER CHARACTERISTICS
MIN
LTC1287B
TYP MAX
±3.0
±0.5
±0.5
12
MIN
LTC1287C
TYP MAX
±3.0
±
0.5
±1.0
12
UNITS
LSB
LSB
LSB
Bits
V
(Note 7)
On Channel = 3V
Off Channel = 0V
On Channel = 0V
Off Channel = 3V
q
q
q
q
– 0.05V to V
CC
+ 0.05V
±1
±1
±1
±1
±1
±1
±1
±1
Off Channel Leakage Current (Note 8)
On Channel = 3V
Off Channel = 0V
On Channel = 0V
Off Channel = 3V
AC CHARACTERISTICS
SYMBOL
f
CLK
t
SMPL
t
CONV
t
CYC
t
dDO
t
dis
t
en
PARAMETER
Clock Frequency
Analog Input Sample Time
Conversion Time
Total Cycle Time
The
q
denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
(Note 6)
See Operating Sequence
See Operating Sequence
See Operating Sequence (Note 6)
See Test Circuits
See Test Circuits
See Test Circuits
q
q
q
LTC1287B/LTC1287C
MIN
TYP
MAX
(Note 9)
1.5
12
14 CLK+5.0µs
250
80
130
450
160
250
0.5
UNITS
MHz
CLK Cycles
CLK Cycles
Cycles
ns
ns
ns
1287fa
Delay Time, CLK↓ to D
OUT
Data Valid
Delay Time, CS↑ to D
OUT
Hi-Z
Delay Time, CLK↓ to D
OUT
Enabled
2
U
µA
µA
µA
µA
W
U
U
W W
W U
W
U
LTC1287
AC CHARACTERISTICS
SYMBOL
t
hDO
t
f
t
r
t
WHCLK
t
WLCLK
t
suCS
t
WHCS
t
WLCS
C
IN
PARAMETER
Time Output Data Remains Valid After CLK↓
D
OUT
Fall Time
D
OUT
Rise Time
CLK High Time
CLK Low Time
Setup Time, CS↓ Before CLK↑
CS High Time Between Data Transfer Cycles
CS Low Time During Data Transfer
Input Capacitance
See Test Circuits
See Test Circuits
V
CC
= 3V (Note 6)
V
CC
= 3V (Note 6)
V
CC
= 3V (Note 6)
V
CC
= 3V (Note 6)
V
CC
= 3V (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
LTC1287B/LTC1287C
MIN
TYP
MAX
50
40
40
600
800
100
5.0
14
100
5
5
100
100
UNITS
ns
ns
ns
ns
ns
ns
µs
CLK Cycles
pF
pF
pF
apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL
V
IH
V
IL
I
IH
I
IL
V
OH
V
OL
I
OZ
I
SOURCE
I
SINK
I
CC
I
REF
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
Reference Current
CONDITIONS
V
CC
= 3.6V
V
CC
= 3.0V
V
IN
= V
CC
V
IN
= 0V
V
CC
= 3.0V, I
O
= 20µA
I
O
= 400µA
V
CC
= 3.0V, I
O
= 20µA
I
O
= 400µA
V
OUT
= V
CC
, CS High
V
OUT
= 0V, CS High
V
OUT
= 0V
V
OUT
= V
CC
CS High
V
REF
= 2.5V
q
q
q
q
q
q
q
q
q
q
DIGITAL A D DC ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which
LTC1287B/LTC1287C
MIN
TYP
MAX
2.1
0.45
2.5
–2.5
2.7
2.90
2.85
0.05
0.10
0.3
3
–3
–10
9
1.5
10
5
50
UNITS
V
V
µA
µA
V
V
V
V
µA
µA
mA
mA
mA
µA
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.
Note 6:
Recommended operating conditions.
U
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.
1287fa
3
LTC1287
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
2.8
2.6
2.4
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6
SUPPLY VOLTAGE (V)
LTC1287 G1
OFFSET (LSB = 1/4096
×
V
REF
)
CLK = 500kHz
T
A
= 25°C
Change in Linearity vs Reference
Voltage
CHANGE IN LINEARITY (LSB = 1/4096
×
V
REF
)
0.5
CHANGE IN GAIN (LSB = 1/4096
×
V
REF
)
MAGNITUDE OF OFFSET CHANGE (LSB)
V
CC
= 3V
0.4
0.3
0.2
0.1
0
0
0.5
2.5
1.0
1.5
2.0
REFERENCE VOLTAGE (V)
Change in Linearity vs
Temperature
0.5
MAGNITUDE OF LINEARITY CHANGE (LSB)
MAGNITUDE OF GAIN CHANGE (LSB)
D
OUT
DELAY TIME FROM CLK↓ (ns)
0.4
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
0.3
0.2
0.1
0
40
20
0
60
–40 –20
80
AMBIENT TEMPERATURE (°C)
4
U W
3.0
LTC1287 G4
Supply Current vs Temperature
1.9
1.8
1.7
1.6
1.5
1.4
1.3
–40 –25 –10
CLK = 500kHz
V
CC
= 3V
Unadjusted Offset Voltage vs
Reference Voltage
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
V
OS
= 0.125mV
V
OS
= 0.250mV
V
CC
= 3V
5 20 35 50 65
TEMPERATURE (°C)
80
95
0
0.5
2.5
1.0
1.5
2.0
REFERENCE VOLTAGE (V)
3.0
LTC1287 G2
LTC1287 G3
Change in Gain vs Reference
Voltage
0
V
CC
= 3V
0.5
Change in Offset vs Temperature
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
–0.1
0.4
–0.2
0.3
–0.3
0.2
–0.4
0.1
–0.5
0
0.5
2.5
1.0
1.5
2.0
REFERENCE VOLTAGE (V)
3.0
0
40
20
0
60
–40 – 20
80
AMBIENT TEMPERATURE (°C)
100
LTC1287 G5
LTC1287 G6
Change in Gain vs Temperature
0.5
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
350
D
OUT
Delay Time vs Temperature
V
CC
= 3V
300
MSB-FIRST DATA
250
200
LSB-FIRST DATA
150
100
50
0
–40 –20
0.4
0.3
0.2
0.1
100
0
40
20
0
60
–40 –20
80
AMBIENT TEMPERATURE (°C)
100
40
80
20
60
0
AMBIENT TEMPERATURE (°C)
100
LTC1287 G7
LTC1287 G8
LTC1287 G9
1287fa
LTC1287
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Clock Rate vs Source
Resistance
500
MAXIMUM CLK FREQUENCY* (MHz)
MINIMUM CLK FREQUENCY (MHz)
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
V
CC
= 3V
0.25
MAXIMUM R
FILTER
*** (Ω)
V
IN
400
300
200
+V
IN
+IN
–IN
100
R
SOURCE
–
0
100
1k
10k
R
SOURCE
– (Ω)
Sample-and-Hold Acquisition
Time vs Source Resistance
100
S & H ACQUISITION TIME TO 0.02% (µs)
INPUT CHANNEL LEAKAGE CURRENT (nA)
800
700
600
500
400
300
200
100
ON CHANNEL
OFF CHANNEL
PEAK-TO-PEAK NOISE ERROR (LSB)
V
REF
= 2.5V
V
CC
= 3V
T
A
= 25°C
0V TO 2.5V INPUT STEP
R
SOURCE
+
10
V
IN
+
–
1
100
1k
R
SOURCE
+ (Ω)
* 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.
PI FU CTIO S
CS (Pin 1):
Chip Select Input. A logic low on this input
enables the LTC1287.
+IN, –IN (Pin 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.
V
REF
(Pin 5):
Reference Input. The reference input defines
the span of the A/D converter and must be kept free of
noise with respect to GND.
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
(Pin 8):
Positive Supply. This supply must be kept free
of noise and ripple by bypassing directly to the analog
ground plane.
U W
LTC G10
Minimum Clock Rate for 0.1LSB
Error**
10k
Maximum Filter Resistor vs Cycle
Time
R
FILTER
1k
C
FILTER
≥1µF
+
–
0.20
0.15
0.10
0.05
100
10
100k
–50
75
0
25
50
–25
AMBIENT TEMPERATURE (°C)
100
1
10
1000
100
CYCLE TIME (µs)
10000
LTC1287 G12
LTC1287 G11
Input Channel Leakage Current vs
Temperature
1000
900
GUARANTEED
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Noise Error vs Reference Voltage
LTC1287 NOISE = 200µV
P-P
10k
LTC1287 G13
0
–50 –30 –10 10 30 50 70 90 110 130
AMBIENT TEMPERATURE (°C)
LTC1287 G14
0
0.5
1.5
2.0
2.5
1.0
REFERENCE VOLTAGE (V)
3.0
LTC1287 G15
*** 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.
U
U
U
1287fa
5
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