LTC1285/LTC1288
3V Micropower Sampling
12-Bit A/D Converters in
SO-8 Packages
DESCRIPTION
The LTC
®
1285/LTC1288 are 3V micropower, 12-bit, suc-
cessive approximation sampling A/D converters. They
typically draw only 160µA 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
s
s
s
s
s
s
s
s
s
s
s
s
s
12-Bit Resolution
8-Pin SO Plastic Package
Low Cost
Low Supply Current: 160µA Typ
Auto Shutdown to 1nA Typ
Guaranteed
±3/4LSB
Max DNL
Single Supply 3V to 6V Operation
Differential Inputs (LTC1285)
2-Channel MUX (LTC1288)
On-Chip Sample-and-Hold
100µs Conversion Time
Sampling Rates:
7.5ksps (LTC1285)
6.6ksps (LTC1288)
I/O Compatible with SPI, Microwire, etc.
APPLICATIONS
s
s
s
s
s
s
Pen Screen Digitizing
Battery-Operated Systems
Remote Data Acquisition
Isolated Data Acquisition
Battery Monitoring
Temperature Measurement
TYPICAL APPLICATIONS
N
12µW, S0-8 Package, 12-Bit ADC
Samples at 200Hz and Runs Off a 3V Supply
1µF
3V
Supply Current vs Sample Rate
1000
T
A
= 25°C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
100
MPU
(e.g., 8051)
1
2
V
REF
V
CC
8
7
P1.4
P1.3
P1.2
SERIAL DATA LINK
LTC1285/88 • TA01
SUPPLY CURRENT (µA)
CLK
+IN
ANALOG INPUT
LTC1285
3
6
0V TO 3V RANGE
–IN
D
OUT
4
5
CS/SHDN
GND
10
1
0.1
1
10
SAMPLE FREQUENCY (kHz)
100
U
U
U
LTC1285/88 • TA02
1
LTC1285/LTC1288
ABSOLUTE
MAXIMUM
RATINGS
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
PACKAGE/ORDER INFORMATION
TOP VIEW
V
REF
1
+IN 2
–IN 3
GND 4
N8 PACKAGE
8-LEAD PDIP
8
7
6
5
V
CC
CLK
D
OUT
CS/SHDN
ORDER PART
NUMBER
LTC1285CN8
T
JMAX
= 150°C,
θ
JA
= 130°C/W
TOP VIEW
CS/SHDN 1
CH0 2
CH1 3
GND 4
N8 PACKAGE
8-LEAD PDIP
T
JMAX
= 150°C,
θ
JA
= 130°C/W
8
7
6
5
V
CC
(V
REF
)
CLK
D
OUT
D
IN
ORDER PART
NUMBER
LTC1288CN8
Consult factory for Industrial and Military grade parts.
RECOM ENDED OPERATING CONDITIONS
SYMBOL
V
CC
f
CLK
t
CYC
t
hDI
t
suCS
t
suDI
t
WHCLK
t
WLCLK
t
WHCS
t
WLCS
PARAMETER
Supply Voltage (Note 3)
Clock Frequency
Total Cycle Time
Hold Time, D
IN
After CLK↑
Setup Time CS↓ Before First CLK↑ (See Operating Sequence)
Setup Time, D
IN
Stable Before CLK↑
CLK High Time
CLK Low Time
CS High Time Between Data Transfer Cycles
CS Low Time During Data Transfer
CONDITIONS
LTC1285
LTC1288
V
CC
= 2.7V
LTC1285, f
CLK
= 120kHz
LTC1288, f
CLK
= 120kHz
V
CC
= 2.7V
LTC1285, V
CC
= 2.7V
LTC1288, V
CC
= 2.7V
V
CC
= 2.7V
V
CC
= 2.7V
V
CC
= 2.7V
V
CC
= 2.7V
LTC1285, f
CLK
= 120kHz
LTC1288, f
CLK
= 120kHz
MIN
2.7
2.7
(Note 4)
125.0
141.5
450
2
2
600
3.5
3.5
2
123.0
139.5
TYP
MAX
6
6
120
UNITS
V
V
kHz
µs
µs
ns
µs
µs
ns
µs
µs
µs
µs
µs
2
U
U
U
U
W
W W
U
W
(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
TOP VIEW
V
REF
1
+IN 2
–IN 3
GND 4
8
7
6
5
V
CC
CLK
D
OUT
CS/SHDN
ORDER PART
NUMBER
LTC1285CS8
PART MARKING
1285C
ORDER PART
NUMBER
LTC1288CS8
PART MARKING
1288C
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 175°C/W
TOP VIEW
CS/SHDN 1
CH0 2
CH1 3
GND 4
8
7
6
5
V
CC
(V
REF
)
CLK
D
OUT
D
IN
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 175°C/W
U WW
LTC1285/LTC1288
CONVERTER AND
MULTIPLEXER
CHARACTERISTICS
PARAMETER
Resolution (No Missing Codes)
Integral Linearity Error
Differential Linearity Error
Offset Error
Gain Error
Analog Input Range
REF Input Range (LTC1285)
(Notes 7, 8, and 9)
Analog Input Leakage Current (Note 10)
(Note 7 and 8)
2.7
≤
V
CC
≤
6V
q
DIGITAL AND DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
IH
V
IL
I
IH
I
IL
V
OH
V
OL
I
OZ
I
SOURCE
I
SINK
R
REF
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
Hi-Z Output Leakage
Output Source Current
Output Sink Current
Reference Input Resistance
(LTC1285)
Reference Current (LTC1285)
CONDITIONS
V
CC
= 3.6V
V
CC
= 2.7V
V
IN
= V
CC
V
IN
= 0V
V
CC
= 2.7V, I
O
= 10µA
V
CC
= 2.7V, I
O
= 360µA
V
CC
= 2.7V, I
O
= 400µA
CS = High
V
OUT
= 0V
V
OUT
= V
CC
CS = V
IH
CS = V
IL
CS = V
CC
t
CYC
≥
640µs, f
CLK
≤
25kHz
t
CYC
= 134µs, f
CLK
= 120kHz
CS = V
CC
LTC1285, t
CYC
≥
640µs, f
CLK
≤
25kHz
LTC1285, t
CYC
= 134µs, f
CLK
= 120kHz
LTC1288, t
CYC
≥
720µs, f
CLK
≤
25kHz
LTC1288, t
CYC
= 150µs, f
CLK
= 120kHz
q
q
q
q
q
q
q
q
q
q
q
q
q
I
CC
Supply Current
DYNAMIC ACCURACY
SYMBOL
S/(N +D)
THD
SFDR
PARAMETER
Signal-to-Noise Plus Distortion Ratio
Total Harmonic Distortion (Up to 5th Harmonic)
Spurious-Free Dynamic Range
Peak Harmonic or Spurious Noise
W U
U
W U
U
(Note 5)
LTC1288
MIN
TYP
MAX
12
±3/4
±1/4
±3/4
±2
±2
±3/4
±3
±8
UNITS
Bits
LSB
LSB
LSB
LSB
V
V
V
±1
µA
CONDITIONS
q
LTC1285
MIN
TYP
MAX
12
±3/4
±1/4
±3/4
±2
±2
±3/4
±3
q
q
q
q
q
(Note 6)
±8
– 0.05V to V
CC
+ 0.05V
1.5V to V
CC
+ 0.05V
±1
(Note 5)
MIN
2
0.8
2.5
– 2.5
2.4
2.1
2.64
2.30
0.4
±3
– 10
15
2700
54
0.001
50
50
0.001
150
160
200
210
2.5
70
±3.0
320
390
TYP
MAX
UNITS
V
V
µA
µA
V
V
V
µA
mA
mA
MΩ
kΩ
µA
µA
µA
µA
µA
µA
µA
µA
f
SMPL
= 7.5kHz (LTC1285), f
SMPL
= 6.6kHz (LTC1288) (Note 5)
CONDITIONS
1kHz Input Signal
1kHz Input Signal
1kHz Input Signal
1kHz Input Signal
MIN
TYP
67
– 80
88
– 88
MAX
UNITS
dB
dB
dB
dB
3
LTC1285/LTC1288
AC CHARACTERISTICS
SYMBOL
t
SMPL
PARAMETER
Analog Input Sample Time
f
SMPL (MAX)
Maximum Sampling Frequency
t
CONV
t
dDO
t
dis
t
en
t
hDO
t
f
t
r
C
IN
Conversion Time
Delay Time, CLK↓ to D
OUT
Data Valid
Delay Time, CS↑ to D
OUT
Hi-Z
Delay Time, CLK↓ to D
OUT
Enable
Time Output Data Remains Valid After CLK↓
D
OUT
Fall Time
D
OUT
Rise Time
Input Capacitance
(Note 5)
CONDITIONS
See Operating Sequence
LTC1285
LTC1288
See Operating Sequence
See Test Circuits
See Test Circuits
See Test Circuits
C
LOAD
= 100pF
See Test Circuits
See Test Circuits
Analog Inputs, On Channel
Analog Inputs, Off Channel
Digital Input
q
q
q
q
q
MIN
q
q
7.5
6.6
TYP
1.5
MAX
UNITS
CLK Cycles
kHz
kHz
12
600
220
180
520
60
80
20
5
5
180
180
1500
660
500
CLK Cycles
ns
ns
ns
ns
ns
ns
pF
pF
pF
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Sample Rate
1000
T
A
= 25°C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
100
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
LTC1288
SUPPLY CURRENT (µA)
10
LTC1285
1
0.1
1
SAMPLE RATE (kHz)
LTC1285/88 • TPC01
4
U W
10
Supply Current vs Temperature
250
LTC1288
f
SMPL
= 6.6kHz
200
LTC1285
f
SMPL
= 7.5kHz
150
Shutdown Supply Current vs Clock
Rate with CS High and CS Low
9
8
7
6
5
4
3
2
1
0.002
0
1
20
60
80
40
FREQUENCY (kHz)
100
120
CS = V
CC
CS = 0
(AFTER CONVERSION)
T
A
= 25°C
V
CC
= 2.7V
V
REF
= 2.5V
100
50
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
5 25 45 65 85 105 125
TEMPERATURE (°C)
LTC1285/88 • TPC02
0
–55 –35 –15
LTC1285/88 • TPC03
LTC1285/LTC1288
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Current vs
Sample Rate (LTC1285)
50
45
T
A
= 25°C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
52
REFERENCE CURRENT (µA)
CHANGE IN OFFSET (LSB = 1/4096
×
V
REF
)
REFERENCE CURRENT (µA)
40
35
30
25
20
15
10
5
0
0
1
2
6
4
3
5
SAMPLE RATE (kHz)
LTC1285/88 • TPC04
Change in Offset vs Temperature
0.20
V
CC
= 2.7V
0.15 V
REF
= 2.5V
f
CLK
= 120kHz
0.10 f
SMPL
= f
SMPL(MAX)
0.05
0
– 0.05
– 0.10
– 0.15
– 0.20
0
10
20
40
50
30
TEMPERATURE (°C)
60
70
0.50
0.45
CHANGE IN LINEARITY (LSB)
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
CHANGE IN OFFSET (LSB)
CHANGE IN GAIN (LSB)
LTC1285/88 • TPC07
Differential Nonlinearity vs Code
DIFFERENTIAL NONLINEARITY ERROR (LSB)
1
EFFECTIVE NUMBER OF BITS (ENOBs)
0.5
T
A
= 25°C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
0
– 0.5
–1
0
512 1024 1536 2048 2560 3072 3584 4096
CODE
LTC1285/88 • TPC11
U W
7
8
Reference Current vs Temperature
53
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
3.0
2.5
2.0
1.5
1.0
0.5
0
Change in Offset
vs Reference Voltage
T
A
= 25°C
V
CC
= 2.7V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
51
50
49
48
47
46
45
44
43
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
LTC1285/88 • TPC05
0.5
1.0
1.5
2.0
2.5
REFERENCE VOLTAGE (V)
3.0
LTC1285/88 • TPC06
Change in Linearity
vs Reference Voltage
–10
T
A
= 25°C
V
CC
= 2.7V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
–9
–8
–7
–6
–5
–4
–3
–2
–1
0
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
REFERENCE VOLTAGE (V)
LTC1285/88 • TPC08
Change in Gain
vs Reference Voltage
T
A
= 25°C
V
CC
= 2.7V
f
CLK
= 120kHz
f
SMPL
= 7.5kHz
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
REFERENCE VOLTAGE (V)
LTC1285/88 • TPC09
Effective Bits and S/(N + D)
vs Input Frequency
12
11
10
9
8
7
6
5
4
3
2
1
0
1
10
INPUT FREQUENCY (kHz)
100
T
A
= 25°C
V
CC
= 2.7V
f
CLK
= 120kHz
74
68
62
56
50
S/(N + D) (dB)
LTC1285/88 • TPC12
5
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