LTC1090CSW datasheet(23/28 Pages) LINER

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LTC1090

1090fc

SNEAK-A-BIT

The LTC1090’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 10-bit + sign word is returned to memory

inside the MPU. The MC68HC05C4 was chosen as an

example; however, any processor could be used.

Two 10-bit unipolar conversions are performed: the first

over a 0 to 5V span and the second over a 0 to –5V span

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

input is determined by which of the two spans contained

it. Then the resulting number (ranging from –1023 to 1023

decimal) is converted to 2’s complement notation and

stored in RAM.

A “Quick Look” Circuit for the LTC1090

Scope Trace of LTC1090 “Quick Look” Circuit

Showing A/D Output of 0101010101 (155HEX)

A “Quick Look” Circuit for the LTC1090

Users can get a quick look at the function and timing of the

LTC1090 by using the following simple circuit. REF+ and

DIN are tied to VCC selecting a 5V input span, CH7 as a

single ended input, unipolar mode, MSB first format and

16-bit word length. ACLK and SCLK are tied together and

driven by an external clock. CS is driven at 1/64 the clock

rate by the CD4520 and DOUT outputs the data. All other

pins are tied to a ground plane. The output data from the

DOUT pin can be viewed on an oscilloscope which is set up

to trigger on the falling edge of CS.

TYPICAL APPLICATIO

SNEAK-A-BIT Circuit

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

LTC1090 • TA04

10µF

VIN

–5V TO 5V

OTHER CHANNELS

OR SNEAK-A-BIT

INPUTS

CH0

CH1

CH2

CH3

CH4

CH5

SCK

MOSI

MISO

CH6

CH7

0.1µF

–5V

COM

DGND

VCC

ACLK

SCLK

DIN

DOUT

REF +

REF –

V –

AGND

LTC1090

MC68HC05C4

2MHz

CLOCK

LT1021-5

DOUT

DEGLITCHER

TIME

MSB

(B9)

LSB

(B0)

FILLS

ZERO

LTC1090 • TA03

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

COM

DGND

VCC

ACLK

SCLK

DIN

DOUT

REF +

REF –

V –

AGND

LTC1090

CLK

f/64

4.7µF

RESET

0.1

RESET

VSS

VIN

VDD

CLK

LTC1090

CLOCK IN

1MHz MAX

TO OSCILLOSCOPE

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