AD7699 datasheet(16/28 Pages) AD

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AD7682/AD7689

Rev. 0 | Page 16 of 28

TRANSFER FUNCTIONS

With the inputs configured for unipolar range (single ended,

COM with ground sense, or paired differentially with INx− as

ground sense), the data output is straight binary.

With the inputs configured for bipolar range (COM = VREF/2 or

paired differentially with INx− = VREF/2), the data outputs are

twos complement.

The ideal transfer characteristic for the AD7682/AD7689 is

shown in Figure 25 and for both unipolar and bipolar ranges

with the internal 4.096 V reference.

100...000

100...001

100...010

011...101

011...110

011...111

TWOS

COMPLEMENT

STRAIGHT

BINARY

000...000

000...001

000...010

111...101

111...110

111...111

ANALOG INPUT

+FSR – 1.5LSB

+FSR – 1LSB

–FSR + 1LSB

–FSR

–FSR + 0.5LSB

Figure 25. ADC Ideal Transfer Function

Table 7. Output Codes and Ideal Input Voltages

Description

Unipolar Analog Input1

VREF = 4.096 V

Digital Output Code

(Straight Binary Hex)

Bipolar Analog Input2

VREF = 4.096 V

Digital Output Code

(Twos Complement Hex)

FSR − 1 LSB

4.095938 V

0xFFFF

2.047938 V

0x7FFF

Midscale + 1 LSB

2.048063 V

0x8001

62.5 μV

0x0001

Midscale

2.048 V

0x8000

0 V

0x00004

Midscale − 1 LSB

2.047938 V

0x7FFF

−62.5 μV

0xFFFF3

−FSR + 1 LSB

62.5 μV

0x0001

−2.047938 V

0x8001

−FSR

0 V

0x0000

−2.048 V

0x8000

1 With COM or INx− = 0 V or all INx referenced to GND.

2 With COM or INx− = VREF /2.

3 This is also the code for an overranged analog input ((INx+) − (INx−), or COM, above VREF − VGND).

4 This is also the code for an underranged analog input ((INx+) − (INx−), or COM, below VGND).

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