LTC1294BCSW datasheet(12/28 Pages) LINER

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LTC1293/LTC1294/LTC1296

129346fs

APPLICATI

I FOR ATIO

Bipolar Transfer Curve (UNI = 0)

OUTPUT CODE

1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 0

•

1 0 0 0 0 0 0 0 0 0 0 1

1 0 0 0 0 0 0 0 0 0 0 0

INPUT VOLTAGE

–1LSB

–2LSB

•

–(VREF) + 1LSB

– (VREF)

INPUT VOLTAGE

(VREF = 5V)

–0.0024V

–0.0048V

•

–4.9976V

–5.00000V

OUTPUT CODE

0 1 1 1 1 1 1 1 1 1 1 1

0 1 1 1 1 1 1 1 1 1 1 0

•

0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0

INPUT VOLTAGE

VREF – 1LSB

VREF – 2LSB

•

1LSB

INPUT VOLTAGE

(VREF = 5V)

4.9976V

4.9851V

•

0.0024V

LTC1293 AI04a

Bipolar Output Code (UNI = 0)

INPUT

CONFIGURATION

UNIPOLAR MODE

BIPOLAR MODE

Single-Ended

Lower Value COM

–(REF

+ – REF–) + COM

Upper Value (REF

+ – REF–) + COM (REF+ – REF–) + COM

Differential

Lower Value IN

–

–(REF

+ – REF–) + IN–

Upper Value (REF

+ – REF–) + IN–

(REF

+ – REF–) + IN–

The following discussion will demonstrate how the two

reference pins are to be used in conjunction with the

analog input multiplexer. In unipolar mode the input span

of the A/D is set by the difference in voltage on the REF

+ pin

and the REF

– pin. In the bipolar mode the input span is

twice the difference in voltage on the REF+ pin and the

REF

– pin. In the unipolar mode the lower value of the input

span is set by the voltage on the COM pin for single-ended

inputs and by the voltage on the minus input pin for

differential inputs. For the bipolar mode of operation the

voltage on the COM pin or the minus input pin set the

center of the input span.

The upper and lower value of the input span can now be

summarized in the following table:

The reference voltages REF+ and REF

– can fall between

VCC and V

–, but the difference (REF+ –REF–) must be less

than or equal to VCC. The input voltages must be less than

or equal to VCC and greater than or equal to V

–. For the

LTC1293 REF

– = 0V.

The following examples are for a single-ended input con-

figuration.

Example 1: Let VCC = 5V, V

– = 0V, REF+ = 4V, REF– = 1V

and COM = 0V. Unipolar mode of operation. The resulting

input span is 0V

≤ IN+ ≤ 3V.

VIN

1 1 1 1 1 1 1 1 1 1 1 1

0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0

0 1 1 1 1 1 1 1 1 1 1 0

0 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 0

•

1 0 0 0 0 0 0 0 0 0 0 1

1 0 0 0 0 0 0 0 0 0 0 0

•

LTC1293 AI04b

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