1
LTC1285/LTC1288
3V Micropower Sampling
12-Bit A/D Converters in
SO-8 Packages
s
12-Bit Resolution
s
8-Pin SO Plastic Package
s
Low Cost
s
Low Supply Current: 160
A Typ
s
Auto Shutdown to 1nA Typ
s
Guaranteed
3/4LSB Max DNL
s
Single Supply 3V to 6V Operation
s
Differential Inputs (LTC1285)
s
2-Channel MUX (LTC1288)
s
On-Chip Sample-and-Hold
s
100
s Conversion Time
s
Sampling Rates:
7.5ksps (LTC1285)
6.6ksps (LTC1288)
s
I/O Compatible with SPI, Microwire, etc.
The LTC
1285/LTC1288 are 3V micropower, 12-bit, suc-
cessive approximation sampling A/D converters. They
typically draw only 160
A of supply current when con-
verting and automatically power down to a typical supply
current of 1nA whenever they are not performing conver-
sions. They are packaged in 8-pin SO packages and
operate on 3V to 6V supplies. These 12-bit, switched-
capacitor, successive approximation ADCs include
sample-and-holds. The LTC1285 has a single differential
analog input. The LTC1288 offers a software selectable
2-channel MUX.
On-chip serial ports allow efficient data transfer to a wide
range of microprocessors and microcontrollers over three
wires. This, coupled with micropower consumption, makes
remote location possible and facilitates transmitting data
through isolation barriers.
These circuits can be used in ratiometric applications or
with an external reference. The high impedance analog
inputs and the ability to operate with reduced spans (to
1.5V full scale) allow direct connection to sensors and
transducers in many applications, eliminating the need for
gain stages.
APPLICATIO
N
S
U
SAMPLE FREQUENCY (kHz)
0.1
1
SUPPLY CURRENT (
A)
10
100
1000
1
10
100
LTC1285/88 TA02
T
A
= 25C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
Supply Current vs Sample Rate
s
Pen Screen Digitizing
s
Battery-Operated Systems
s
Remote Data Acquisition
s
Isolated Data Acquisition
s
Battery Monitoring
s
Temperature Measurement
12
W, S0-8 Package, 12-Bit ADC
Samples at 200Hz and Runs Off a 3V Supply
3V
1
F
ANALOG INPUT
0V TO 3V RANGE
IN
GND
V
CC
CLK
D
OUT
V
REF
LTC1285
MPU
(e.g., 8051)
P1.4
P1.3
P1.2
+IN
LTC1285/88 TA01
CS/SHDN
6
5
8
7
3
4
1
2
SERIAL DATA LINK
FEATURES
DESCRIPTIO
N
U
TYPICAL APPLICATIO
N
S
N
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
2
LTC1285/LTC1288
(Notes 1 and 2)
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
PART MARKING
T
JMAX
= 150
C,
JA
= 130
C/W
Consult factory for Industrial and Military grade parts.
ORDER PART
NUMBER
LTC1285CN8
ORDER PART
NUMBER
LTC1285CS8
1285C
PART MARKING
ORDER PART
NUMBER
LTC1288CN8
ORDER PART
NUMBER
LTC1288CS8
1288C
T
JMAX
= 150
C,
JA
= 130
C/W
T
JMAX
= 150
C,
JA
= 175
C/W
T
JMAX
= 150
C,
JA
= 175
C/W
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
Supply Voltage (V
CC
) to GND ................................... 12V
Voltage
Analog and Reference ................ 0.3V to V
CC
+ 0.3V
Digital Inputs ......................................... 0.3V to 12V
Digital Output ............................. 0.3V to V
CC
+ 0.3V
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
CC
Supply Voltage (Note 3)
LTC1285
2.7
6
V
LTC1288
2.7
6
V
f
CLK
Clock Frequency
V
CC
= 2.7V
(Note 4)
120
kHz
t
CYC
Total Cycle Time
LTC1285, f
CLK
= 120kHz
125.0
s
LTC1288, f
CLK
= 120kHz
141.5
s
t
hDI
Hold Time, D
IN
After CLK
V
CC
= 2.7V
450
ns
t
suCS
Setup Time CS
Before First CLK
(See Operating Sequence)
LTC1285, V
CC
= 2.7V
2
s
LTC1288, V
CC
= 2.7V
2
s
t
suDI
Setup Time, D
IN
Stable Before CLK
V
CC
= 2.7V
600
ns
t
WHCLK
CLK High Time
V
CC
= 2.7V
3.5
s
t
WLCLK
CLK Low Time
V
CC
= 2.7V
3.5
s
t
WHCS
CS High Time Between Data Transfer Cycles
V
CC
= 2.7V
2
s
t
WLCS
CS Low Time During Data Transfer
LTC1285, f
CLK
= 120kHz
123.0
s
LTC1288, f
CLK
= 120kHz
139.5
s
RECO
M
E
N
DED OPERATI
N
G CO
N
DITIO
N
S
U
U
U
U
W
W
1
2
3
4
8
7
6
5
TOP VIEW
V
REF
+IN
IN
GND
V
CC
CLK
D
OUT
N8 PACKAGE
8-LEAD PDIP
CS/SHDN
1
2
3
4
8
7
6
5
TOP VIEW
CH0
CH1
GND
V
CC
(V
REF
)
CLK
D
OUT
D
IN
N8 PACKAGE
8-LEAD PDIP
CS/SHDN
1
2
3
4
8
7
6
5
TOP VIEW
V
CC
CLK
D
OUT
V
REF
+IN
IN
GND
S8 PACKAGE
8-LEAD PLASTIC SO
CS/SHDN
1
2
3
4
8
7
6
5
TOP VIEW
V
CC
(V
REF
)
CLK
D
OUT
D
IN
CH0
CH1
GND
S8 PACKAGE
8-LEAD PLASTIC SO
CS/SHDN
3
LTC1285/LTC1288
LTC1285
LTC1288
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
Resolution (No Missing Codes)
q
12
12
Bits
Integral Linearity Error
(Note 6)
q
3/4
2
3/4
2
LSB
Differential Linearity Error
q
1/4
3/4
1/4
3/4
LSB
Offset Error
q
3/4
3
3/4
3
LSB
Gain Error
q
2
8
2
8
LSB
Analog Input Range
(Note 7 and 8)
q
V
REF Input Range (LTC1285)
2.7
V
CC
6V
V
(Notes 7, 8, and 9)
V
Analog Input Leakage Current (Note 10)
q
1
1
A
1.5V to V
CC
+ 0.05V
0.05V to V
CC
+ 0.05V
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
S/(N +D)
Signal-to-Noise Plus Distortion Ratio
1kHz Input Signal
67
dB
THD
Total Harmonic Distortion (Up to 5th Harmonic)
1kHz Input Signal
80
dB
SFDR
Spurious-Free Dynamic Range
1kHz Input Signal
88
dB
Peak Harmonic or Spurious Noise
1kHz Input Signal
88
dB
DY
N
A
M
IC ACCURACY
U
W
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IH
High Level Input Voltage
V
CC
= 3.6V
q
2
V
V
IL
Low Level Input Voltage
V
CC
= 2.7V
q
0.8
V
I
IH
High Level Input Current
V
IN
= V
CC
q
2.5
A
I
IL
Low Level Input Current
V
IN
= 0V
q
2.5
A
V
OH
High Level Output Voltage
V
CC
= 2.7V, I
O
= 10
A
q
2.4
2.64
V
V
CC
= 2.7V, I
O
= 360
A
q
2.1
2.30
V
V
OL
Low Level Output Voltage
V
CC
= 2.7V, I
O
= 400
A
q
0.4
V
I
OZ
Hi-Z Output Leakage
CS = High
q
3
A
I
SOURCE
Output Source Current
V
OUT
= 0V
10
mA
I
SINK
Output Sink Current
V
OUT
= V
CC
15
mA
R
REF
Reference Input Resistance
CS = V
IH
2700
M
(LTC1285)
CS = V
IL
54
k
I
REF
Reference Current (LTC1285)
CS = V
CC
q
0.001
2.5
A
t
CYC
640
s, f
CLK
25kHz
50
A
t
CYC
= 134
s, f
CLK
= 120kHz
q
50
70
A
I
CC
Supply Current
CS = V
CC
q
0.001
3.0
A
LTC1285, t
CYC
640
s, f
CLK
25kHz
150
A
LTC1285, t
CYC
= 134
s, f
CLK
= 120kHz
q
160
320
A
LTC1288, t
CYC
720
s, f
CLK
25kHz
200
A
LTC1288, t
CYC
= 150
s, f
CLK
= 120kHz
q
210
390
A
DIGITAL A
N
D DC ELECTRICAL CHARACTERISTICS
U
CO
N
VERTER A
N
D
M
ULTIPLEXER CHARACTERISTICS
U
W
U
(Note 5)
(Note 5)
f
SMPL
= 7.5kHz (LTC1285), f
SMPL
= 6.6kHz (LTC1288) (Note 5)
4
LTC1285/LTC1288
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t
SMPL
Analog Input Sample Time
See Operating Sequence
1.5
CLK Cycles
f
SMPL (MAX)
Maximum Sampling Frequency
LTC1285
q
7.5
kHz
LTC1288
q
6.6
kHz
t
CONV
Conversion Time
See Operating Sequence
12
CLK Cycles
t
dDO
Delay Time, CLK
to D
OUT
Data Valid
See Test Circuits
q
600
1500
ns
t
dis
Delay Time, CS
to D
OUT
Hi-Z
See Test Circuits
q
220
660
ns
t
en
Delay Time, CLK
to D
OUT
Enable
See Test Circuits
q
180
500
ns
t
hDO
Time Output Data Remains Valid After CLK
C
LOAD
= 100pF
520
ns
t
f
D
OUT
Fall Time
See Test Circuits
q
60
180
ns
t
r
D
OUT
Rise Time
See Test Circuits
q
80
180
ns
C
IN
Input Capacitance
Analog Inputs, On Channel
20
pF
Analog Inputs, Off Channel
5
pF
Digital Input
5
pF
(Note 5)
AC CHARACTERISTICS
The
q
denotes specifications which apply over the full operating
temperature range.
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 GND.
Note 3: These devices are specified at 3V. For 5V specified devices, see
LTC1286 and LTC1298.
Note 4: Increased leakage currents at elevated temperatures cause the
sample-and-hold to droop, therefore it is recommended that f
CLK
75kHz
at 70
and f
CLK
1kHz at 25
C.
Note 5: V
CC
= 2.7V, V
REF
= 2.5V and CLK = 120kHz unless otherwise
specified.
Note 6: Linearity error is specified between the actual end points of the
A/D transfer curve.
Note 7: Two on-chip diodes are tied to each reference and analog input
which will conduct for reference or analog input voltages one diode drop
below GND or one diode drop above V
CC
. This spec allows 50mV forward
bias of either diode for 2.7V
V
CC
6V. This means that as long as the
reference or analog input does not exceed the supply voltage by more than
50mV the output code will be correct. To achieve an absolute 0V to 2.7V
input voltage range will therefore require a minimum supply voltage of
2.650V over initial tolerance, temperature variations and loading. For 2.7V
< V
CC
6V, reference and analog input range cannot exceed 6.05V. If
reference and analog input range are greater than 6.05V, the output code
will not be guaranteed to be correct.
Note 8: The supply voltage range for the LTC1285 and the LTC1288 is
from 2.7V to 6V.
Note 9: Recommended operating conditions
Note 10: Channel leakage current is measured after the channel selection.
SAMPLE RATE (kHz)
0.1
1
SUPPLY CURRENT (
A)
10
1000
100
1
10
LTC1285/88 TPC01
LTC1288
LTC1285
T
A
= 25C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
Supply Current vs Sample Rate
FREQUENCY (kHz)
1
0
SUPPLY CURRENT (
A)
1
2
3
4
5
6
20
40
60
80
LTC1285/88 TPC03
100
7
8
9
0.002
120
T
A
= 25C
V
CC
= 2.7V
V
REF
= 2.5V
CS = 0
(AFTER CONVERSION)
CS = V
CC
Shutdown Supply Current vs Clock
Rate with CS High and CS Low
TEMPERATURE (C)
55
SUPPLY CURRENT (
A)
150
200
250
105
LTC1285/88 TPC02
100
50
0
15
25
65
35
125
5
45
85
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
LTC1285
f
SMPL
= 7.5kHz
LTC1288
f
SMPL
= 6.6kHz
Supply Current vs Temperature
5
LTC1285/LTC1288
TEMPERATURE (C)
0
CHANGE IN OFFSET (LSB)
0.15
30
LTC1285/88 TPC07
0
0.10
10
20
40
0.15
0.20
0.20
0.10
0.05
0.05
50
60
70
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
f
SMPL
= f
SMPL(MAX)
Change in Offset vs Temperature
Reference Current vs
Sample Rate (LTC1285)
SAMPLE RATE (kHz)
0
0
REFERENCE CURRENT (
A)
5
15
20
25
50
35
2
4
5
LTC1285/88 TPC04
10
40
45
30
1
3
6
7
8
T
A
= 25C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
REFERENCE VOLTAGE (V)
1.0
0
CHANGE IN GAIN (LSB)
1
3
4
5
10
7
1.4
1.8 2.0
2.8
LTC1285/88 TPC09
2
8
9
6
1.2
1.6
2.2 2.4 2.6
T
A
= 25C
V
CC
= 2.7V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
Change in Gain
vs Reference Voltage
Change in Offset
vs Reference Voltage
TEMPERATURE (C)
55
43
REFERENCE CURRENT (
A)
44
46
47
48
53
50
15
25
45
125
LTC1285/88 TPC05
45
51
52
49
35
5
65
85 105
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
Reference Current vs Temperature
Change in Linearity
vs Reference Voltage
REFERENCE VOLTAGE (V)
1.0
0
CHANGE IN LINEARITY (LSB)
0.05
0.15
0.20
0.25
0.50
0.35
1.4
1.8 2.0
2.8
LTC1285/88 TPC08
0.10
0.40
0.45
0.30
1.2
1.6
2.2 2.4 2.6
T
A
= 25C
V
CC
= 2.7V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
REFERENCE VOLTAGE (V)
0.5
0
CHANGE IN OFFSET (LSB = 1/4096
V
REF
)
0.5
1.0
1.5
2.0
2.5
3.0
1.0
1.5
2.0
2.5
LTC1285/88 TPC06
3.0
T
A
= 25C
V
CC
= 2.7V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
Effective Bits and S/(N + D)
vs Input Frequency
INPUT FREQUENCY (kHz)
1
0
EFFECTIVE NUMBER OF BITS (ENOBs)
S/(N + D) (dB)
3
5
7
10
10
100
LTC1285/88 TPC12
1
4
6
9
12
11
8
62
56
74
68
50
2
T
A
= 25C
V
CC
= 2.7V
f
CLK
= 120kHz
Differential Nonlinearity vs Code
CODE
0
1
DIFFERENTIAL NONLINEARITY ERROR (LSB)
0.5
0
0.5
1
512 1024 1536 2048
LTC1285/88 TPC11
2560 3072 3584 4096
T
A
= 25C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
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