LTC1287
3V Single Chip 12-Bit
Data Acquisition System
FEATURES
s
s
s
DESCRIPTIO
s
Single Supply 3.3V or
±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 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.
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
TYPICAL APPLICATI
s
s
s
Battery-Powered Instruments
Data Logger
Data Acquisition Modules
3V Differential Input Data Acquisition System
22µF TANTALUM
+
1.0
CS
DIFFERENTIAL INPUTS
COMMON MODE RANGE
0V TO V
CC
*
V
CC
10k
+IN
LTC1287
–IN
GND
CLK
D
OUT
V
REF
22µF
TANTALUM
ERROR (LSB)
0
+
–
3V
LITHIUM
0.5
+
LT1004-1.2
–0.5
–1.0
0
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.
512
1024
1536
2048
CODE
LTC1287 TA02
1287 TA01
U
INL with V
REF
= 1.2V
2560
3072
3584
4096
UO
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
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
J8 PACKAGE
8-LEAD CERAMIC DIP
N8 PACKAGE
8-LEAD PLASTIC DIP
1287 PO
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)
ULTIPLEXER CHARACTERISTICS
CONDITIONS
V
CC
= 2.7V (Note 4)
V
CC
= 2.7V (Notes 4 & 5)
V
CC
= 2.7V (Note 4)
q
q
q
q
(Note 3)
LTC1287C
MIN
TYP MAX
±3.0
±
0.5
±1.0
12
UNITS
LSB
LSB
LSB
Bits
V
µA
µA
µA
µA
LTC1287B
MIN
TYP MAX
±3.0
±0.5
±0.5
12
(Note 7)
On Channel = 3V
Off Channel = 0V
On Channel = 0V
Off Channel = 3V
q
q
q
q
(V
–
) – 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
(Note 3)
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
Delay Time, CLK↓ to D
OUT
Data Valid
Delay Time, CS↑ to D
OUT
Hi-Z
Delay Time, CLK↓ to D
OUT
Enabled
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
2
U
W
U
U
W W
W U
W
U
LTC1287
AC CHARACTERISTICS
(Note 3)
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
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
DIGITAL A D DC ELECTRICAL CHARACTERISTICS
(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
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.
U
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 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.
3
LTC1287
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
2.8
2.6
2.4
CLK = 500kHz
T
A
= 25°C
OFFSET (LSB = 1/4096
×
V
REF
)
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
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
0.5
MAGNITUDE OF GAIN CHANGE (LSB)
MAGNITUDE OF LINEARITY 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
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Unadjusted Offset Voltage vs
Reference Voltage
V
CC
= 3V
V
OS
= 0.250mV
V
OS
= 0.125mV
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
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
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
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
LTC1287
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Clock Rate vs Source
Resistance
500
MAXIMUM CLK FREQUENCY* (MHz)
MINIMUM CLK FREQUENCY (MHz)
MAXIMUM R
FILTER
*** (Ω)
400
V
CC
= 3V
V
REF
= 2.5V
CLK = 500kHz
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
1000
S & H ACQUISITION TIME TO 0.02% (µs)
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
+
INPUT CHANNEL LEAKAGE CURRENT (nA)
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
#
1
2, 3
4
5
6
7
8
PIN
CS
+IN, –IN
GND
V
REF
D
OUT
CLK
V
CC
FUNCTION
Chip Select Input
Analog Inputs
Analog Ground
Reference Input
Digital Data Output
Shift Clock
Positive Supply
U W
LTC G10
Minimum Clock Rate for 0.1LSB
Error**
10k
V
CC
= 3V
0.25
1k
0.20
0.15
0.10
0.05
1
Maximum Filter Resistor vs Cycle
Time
R
FILTER
C
FILTER
≥1µF
V
IN
+
–
100
10
100k
–50
0
25
50
75
–25
AMBIENT TEMPERATURE (°C)
100
10
100
1000
CYCLE TIME (µs)
10000
LTC1287 G12
LTC1287 G11
Input Channel Leakage Current vs
Temperature
1.0
GUARANTEED
900
Noise Error vs Reference Voltage
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.5
2.5
1.5
2.0
1.0
REFERENCE VOLTAGE (V)
3.0
LTC1287 NOISE = 200µV
P-P
10k
LTC1287 G13
0
–50 –30 –10 10 30 50 70 90 110 130
AMBIENT TEMPERATURE (°C)
LTC1287 G14
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
DESCRIPTION
A logic low on this input enables the LTC1287.
These inputs must be free of noise with respect to GND.
GND should be tied directly to an analog ground plane.
The reference input defines the span of the A/D converter and must be kept free of noise with respect to GND.
The A/D conversion result is shifted out of this output.
This clock synchronizes the serial data transfer.
This supply must be kept free of noise and ripple by bypassing directly to the analog ground plane.
5
