AD7265BCP datasheet(18/28 Pages) AD

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AD7265

Rev. A | Page 18 of 28

TRANSFER FUNCTIONS

DIGITAL INPUTS

The designed code transitions occur at successive integer LSB

values (1 LSB, 2 LSB, and so on). In single-ended mode, the LSB

size is V

The digital inputs applied to the AD7265 are not limited by the

maximum ratings that limit the analog inputs. Instead, the

digital inputs can be applied up to 7 V and are not restricted by

the V

/4096 when the 0 V to V

REF

range is used, and the LSB

size is 2 × V

/4096 when the 0 V to 2 × V

REF

range is used. In

differential mode, the LSB size is 2 × V

+ 0.3 V limit, as are the analog inputs. See the

Absolute

Maximum Ratings

REF

/4096 when the 0 V to

section for more information. Another

advantage of the SCLK, RANGE, A0 to A2, and

REF

range is used, and the LSB size is 4 × VREF/4096 when the

0 V to 2 × V

CS pins not

being restricted by the V

REF

range is used. The ideal transfer characteristic

for the AD7265 when straight binary coding is output is shown

+ 0.3 V limit is that power supply

sequencing issues are avoided. If one of these digital inputs is

applied before V

Figure 32, and the ideal transfer characteristic for the AD7265

when twos complement coding is output is shown (with the 2 ×

, there is no risk of latch-up, as there would

be on the analog inputs if a signal greater than 0.3 V were

applied prior to V

range) in Figure 33.

REF

000...000

111...111

1LSB = VREF/4096

1LSB

VREF – 1LSB

ANALOG INPUT

000...001

000...010

111...110

111...000

011...111

NOTE

1. VREF IS EITHER VREF OR 2 × VREF.

VDRIVE

The AD7265 also has a VDRIVE feature to control the voltage at

which the serial interface operates. VDRIVE allows the ADC to

easily interface to both 3 V and 5 V processors. For example, if

the AD7265 was operated with a V

of 5 V, the V

DRIVE

could be powered from a 3 V supply, allowing a large dynamic

range with low voltage digital processors. Therefore, the

AD7265 could be used with the 2 × V

input range, with a V

REF

of 5 V while still being able to interface to 3 V digital parts.

Figure 32. Straight Binary Transfer Characteristic

100...000

011...111

1LSB = 2

× VREF/4096

+VREF – 1 LSB

–VREF + 1LSB VREF – 1LSB

ANALOG INPUT

100...001

100...010

011...110

000...001

000...000

111...111

Figure 33. Twos Complement Transfer Characteristic with

± V

Input Range

REF

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