LTC1289CC datasheet(24/28 Pages) LINER

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LTC1289

APPLICATI

TYPICAL

SNEAK-A-BIT

The LTC1289’s unique ability to software select the polar-

ity of the differential inputs and the output word length is

used to achieve one more bit of resolution. Using the

circuit below with two conversions and some software, a

2’s complement 12-bit + sign word is returned to memory

inside the MPU. The MC68HC05C4 was chosen as an

example, however, any processor that operates at 3.3V

could be used.

Two 12-bit unipolar conversions are performed: the first

over a 0V to 2.5V span and the second over a 0V to –2.5V

span (by reversing the polarity of the inputs). The sign of

the input is determined by which of the two spans con-

tained it. Then the resulting number (ranging from –4095

to +4095 decimal) is converted to 2’s complement nota-

tion and stored in RAM.

2.5V

1ST CONVERSION

(+) CH6

(–) CH7

1ST CONVERSION

4096 STEPS

2ND CONVERSION

4096 STEPS

–2.5V

2ND CONVERSION

(–) CH6

(+) CH7

VIN

2.5V

–2.5V

SOFTWARE

8191 STEPS

LTC1289 TA04

SNEAK-A-BIT

SNEAK-A-BIT is a trademark of Linear Technology Corp.

SNEAK-A-BIT Circuit

LTC1289 TA03

µF

LT1019

–2.5

MC68HC05C4

SCLK

MOSI

MISO

–3.3V

0.1

µF

2MHz

ACLK

+3.3V

OTHER CHANNELS

OR SNEAK-A-BIT

INPUTS

VIN

–2.5V TO +2.5V

LTC1289

CHO

CH1

CH2

CH3

CH4

CH5

CH6

CH7

COM

DGND

VCC

ACLK

SCLK

DIN

DOUT

REF+

REF–

V–

AGND

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