Linear Technology LTC1287 Datasheet

LTC1287

3V Single Chip 12-Bit

Data Acquisition System

EATU

F

■

Single Supply 3.3V or ±3.3V Operation

■

Built-In Sample-and-Hold

■

Direct 3-Wire Interface to Most MPU Serial Ports and

RE

S

All MPU Parallel Ports

■

30kHz Maximum Throughput Rate

U

KEY SPECIFICATIO S

■

Minimum Guaranteed Supply Voltage: 2.7V

■

Resolution: 12 Bits

■

Fast Conversion Time: 24µs Max Over Temp.

■

Low Supply Current: 1.0mA

U

O

A

PPLICATITYPICAL

■

Battery-Powered Instruments

■

Data Logger

■

Data Acquisition Modules

DUESCRIPTIO

The LTC1287 is a 3V data acquisition component which
contains a serial I/O successive approximation A/D con­verter. The device specifications are guaranteed at a
supply voltage of 2.7V. It uses LTCMOSTM switched ca­pacitor technology to perform a 12-bit unipolar, A/D
conversion. The differential input has an on-chip sample­and-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

3V Differential Input Data Acquisition System INL with V

LTC1287

TANTALUM

D

V

VCC

CLK

OUT

REF

22µF



CS

DIFFERENTIAL INPUTS

COMMON MODE RANGE

FOR OVERVOLTAGE PROTECTION, LIMIT THE INPUT CURRENT TO 15mA

*

PER PIN OR CLAMP THE INPUTS TO VCC AND GND WITH 1N4148 DIODES.
CONVERSION RESULTS ARE NOT VALID WHEN THE SELECTED CHANNEL OR
OTHER CHANNEL IS OVERVOLTAGED (V
ON OVERVOLTAGE PROTECTION IN THE APPLICATIONS INFORMATION.

0V TO V

+

*

CC

–

+IN

–IN

GND

< GND OR VIN > VCC). SEE SECTION

IN

22µF TANTALUM

+

10k

+

TO AND FROM MPU

3V
LITHIUM

LT1004-1.2

1287 TA01

1.0

0.5

0

ERROR (LSB)

–0.5

–1.0

0

512 1024

1536

REF

2048

CODE

= 1.2V

2560 3072

3584 4096

LTC1287 TA02

1

LTC1287

W

O

A

(Notes 1 and 2)

LUTEXI T

S

Supply Voltage (VCC) to GND.................................. 12V

Voltage

Analog and Reference Inputs .... –0.3V to V

Digital Inputs........................................ –0.3V to 12V

Digital Outputs .......................... –0.3V to V

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

A

WUW

ARB

U
G

I

+ 0.3V

CC

+ 0.3V

CC

S

PACKAGE

TOP VIEW

1

CS

2

+IN

3

–IN

45

GND

J8 PACKAGE

8-LEAD CERAMIC DIP

N8 PACKAGE

8-LEAD PLASTIC DIP

/

O

RDER I FOR ATIO

ORDER PART

NUMBER



V

8

CC

7

CLK

6

D



OUT

V

REF

LTC1287BIJ
LTC1287CIJ
LTC1287BIN
LTC1287CIN
LTC1287BCJ
LTC1287CCJ
LTC1287BCN

1287 PO

LTC1287CCN

WU

Lead Temperature (Soldering, 10 sec.)................ 300°C

UU W

CO VERTER A D ULTIPLEXER CHARACTERISTICS

LTC1287B

PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS

Offset Error VCC = 2.7V (Note 4) ● ±3.0 ±3.0 LSB
Linearity Error (INL) VCC = 2.7V (Notes 4 & 5) ● ±0.5 ±0.5 LSB
Gain Error VCC = 2.7V (Note 4) ● ±0.5 ±1.0 LSB
Minimum Resolution for Which No

Missing Codes are Guaranteed
Analog and REF Input Range (Note 7) V
On Channel Leakage Current (Note 8) On Channel = 3V

Off Channel = 0V
On Channel = 0V

Off Channel = 3V

Off Channel Leakage Current (Note 8) On Channel = 3V ● ±1 ±1 µA

Off Channel = 0V
On Channel = 0V

Off Channel = 3V

● 12 12 Bits

● ±1 ±1 µA

● ±1 ±1 µA

● ±1 ±1 µA

(Note 3)

LTC1287C

(V–) – 0.05V to VCC + 0.05V

U

AC CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

f

CLK

t

SMPL

t

CONV

t

CYC

t

dDO

t

dis

t

en

Clock Frequency (Note 6) (Note 9) 0.5 MHz
Analog Input Sample Time See Operating Sequence 1.5 CLK Cycles
Conversion Time See Operating Sequence 12 CLK Cycles
Total Cycle Time See Operating Sequence (Note 6) 14 CLK+ Cycles

Delay Time, CLK↓ to D
Delay Time, CS↑ to D
Delay Time, CLK↓ to D

OUT

OUT

OUT

(Note 3)

LTC1287B/LTC1287C

5.0µs

Data Valid See Test Circuits ● 250 450 ns

Hi-Z See Test Circuits ● 80 160 ns

Enabled See Test Circuits ● 130 250 ns

2

LTC1287

AC CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

t

hDO

t

f

t

r

t

WHCLK

t

WLCLK

t

suCS

t

WHCS

t

WLCS

C

IN

Time Output Data Remains Valid After CLK↓ 50 ns
D

Fall Time See Test Circuits ● 40 100 ns

OUT

D

Rise Time See Test Circuits ● 40 100 ns

OUT

CLK High Time VCC = 3V (Note 6) 600 ns
CLK Low Time VCC = 3V (Note 6) 800 ns
Setup Time, CS↓ Before CLK↑ VCC = 3V (Note 6) 100 ns
CS High Time Between Data Transfer Cycles VCC = 3V (Note 6) 5.0 µs
CS Low Time During Data Transfer VCC = 3V (Note 6) 14 CLK Cycles
Input Capacitance Analog Inputs On Channel 100 pF

(Note 3)

LTC1287B/LTC1287C

Analog Inputs Off Channel 5 pF
Digital Inputs 5 pF

U
D

DIGITAL

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IH

V

IL

I

IH

I

IL

V

OH

V

OL

I

OZ

I

SOURCE

I

SINK

I

CC

I

REF

A

High Level Input Voltage VCC = 3.6V ● 2.1 V
Low Level Input Voltage VCC = 3.0V ● 0.45 V
High Level Input Current VIN = V
Low Level Input Current VIN = 0V ● –2.5 µA
High Level Output Voltage VCC = 3.0V, IO = 20µA 2.90 V

Low Level Output Voltage VCC = 3.0V, IO = 20µA 0.05 V

High Z Output Leakage V

Output Source Current V
Output Sink Current V
Positive Supply Current CS High ● 1.5 5 mA
Reference Current V

DC

LECTRICAL C CHARA TER ST

E

CC

IO = 400µA ● 2.7 2.85 V

IO = 400µA ● 0.10 0.3 V

= VCC, CS High ● 3 µA

OUT

V

= 0V, CS High ● –3 µA

OUT

= 0V –10 mA

OUT

= V

OUT

CC

= 2.5V ● 10 50 µA

REF

ICS

I

(Note 3)

LTC1287B/LTC1287C

● 2.5 µA

9mA

The ● denotes specifications which apply over the operating temperature
range; all other limits and typicals TA = 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
Note 4: One LSB is equal to V

= 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.

= 3V, V

CC

= 2.5V, CLK = 500kHz unless otherwise specified.

REF

divided by 4096. For example, when V

REF

REF

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
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
f

CLK

. Be careful during testing at low VCC levels, as high level analog

CC

≥ 30kHz at 85°C and

≥ 3kHz at 25°C.

CLK

3

LTC1287

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

VCC = 3V

VOS = 0.250mV

VOS = 0.125mV

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

VCC = 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

LPER

F

O

R

ATYPICA

UW

CCHARA TERIST

E

C

ICS

Supply Current vs Supply Voltage

2.8
CLK = 500kHz

2.6

= 25°C

T

A

2.4

2.2

2.0

1.8

1.6

1.4

SUPPLY CURRENT (mA)

1.2

1.0

0.8

2.8 3.0

2.7

2.9
SUPPLY VOLTAGE (V)

3.2 3.6

3.3

3.1



Change in Linearity vs Reference
Voltage

0.5

)

VCC = 3V

REF

0.4

0.3

3.4

3.5

LTC1287 G1

Supply Current vs Temperature

1.9

1.8

1.7

1.6

1.5

SUPPLY CURRENT (mA)

1.4

1.3
–25 5

–40

–10

TEMPERATURE (°C)

35 95

20

Change in Gain vs Reference
Voltage

0

VCC = 3V

)

REF

–0.1

–0.2

CLK = 500kHz

= 3V

V

CC

65

50

LTC1287 G2

Unadjusted Offset Voltage vs
Reference Voltage

80

Change in Offset vs Temperature

0.2

0.1

CHANGE IN LINEARITY (LSB = 1/4096 × V

0

0

1.0 1.5 2.0

0.5
REFERENCE VOLTAGE (V)

Change in Linearity vs
Temperature

0.5
VCC = 3V

= 2.5V

V

REF

CLK = 500kHz

0.4

0.3

0.2

0.1

MAGNITUDE OF LINEARITY CHANGE (LSB)

0

–40

4

0

–20

AMBIENT TEMPERATURE (°C)

–0.3

–0.4

CHANGE IN GAIN (LSB = 1/4096 × V

–0.5

2.5 3.0

LTC1287 G4

0

1.0 1.5 2.0

0.5
REFERENCE VOLTAGE (V)

Change in Gain vs Temperature

0.5
VCC = 3V

= 2.5V

V

REF

CLK = 500kHz

0.4

0.3

0.2

0.1

MAGNITUDE OF GAIN CHANGE (LSB)

0

40

20

60

80

LTC1287 G7

100

–40

0

–20

AMBIENT TEMPERATURE (°C)

40

20

60

2.5 3.0

LTC1287 G5

100

80

LTC1287 G8

D

Delay Time vs Temperature

OUT

LPER

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 = 200µV

P-P

F

O

R

ATYPICA

UW

CCHARA TERIST

E

C

LTC1287

ICS

Maximum Clock Rate vs Source
Resistance

500

400

300

200

+V

+IN

IN

R

100

MAXIMUM CLK FREQUENCY* (MHz)

0

100

–

SOURCE

–IN

1k 10k 100k

R

SOURCE

VCC = 3V
V
CLK = 500kHz

– (Ω)

REF

= 2.5V

Sample-and-Hold Acquisition
Time vs Source Resistance

100

V

= 2.5V

REF

= 3V

V

CC

= 25°C

T

A

0V TO 2.5V INPUT STEP

R

+

SOURCE

V

IN

10

S & H ACQUISITION TIME TO 0.02% (µs)

1
100 1k 10k

+

–

R

SOURCE

+ (Ω)

LTC G10

LTC1287 G13

Minimum Clock Rate for 0.1LSB
Error**



VCC = 3V

0.25

0.20

0.15

0.10

0.05

MINIMUM CLK FREQUENCY (MHz)

–50

02550

–25

AMBIENT TEMPERATURE (°C)

Input Channel Leakage Current vs
Temperature

1000

900
800
700
600
500
400
300
200
100

INPUT CHANNEL LEAKAGE CURRENT (nA)

0

–30 10

–10

–50

AMBIENT TEMPERATURE (°C)

GUARANTEED

ON CHANNEL

OFF CHANNEL

70 90

50 130

30

75 100

LTC1287 G11

110

LTC1287 G14

Maximum Filter Resistor vs Cycle
Time

10k

R

FILTER

V

IN

C

≥1µF

FILTER

1k

*** (Ω)

100

FILTER

10

MAXIMUM R

1

10 1000 10000

+

–

100

CYCLE TIME (µs)

Noise Error vs Reference Voltage

LTC1287 G12

* 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.

U

PI FU CTIO S

# 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.
5V
6D

REF
OUT

7 CLK Shift Clock This clock synchronizes the serial data transfer.
8V

CC

*** MAXIMUM R

CHANGE IN FULL SCALE ERROR FROM ITS VALUE AT R
DETECTED.

REPRESENTS THE FILTER RESISTOR VALUE AT WHICH A 0.1LSB

FILTER

= 0Ω IS FIRST

FILTER

UU

Reference Input The reference input defines the span of the A/D converter and must be kept free of noise with respect to GND.
Digital Data Output The A/D conversion result is shifted out of this output.

Positive Supply This supply must be kept free of noise and ripple by bypassing directly to the analog ground plane.

5