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AD7265

Data Sheet

Rev. B | Page 18 of 28

TRANSFER FUNCTIONS

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 VREF/4096 when the 0 V to VREF range is used, and the LSB

size is 2 × VREF/4096 when the 0 V to 2 × VREF range is used. In

differential mode, the LSB size is 2 × VREF/4096 when the 0 V to

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

0 V to 2 × VREF range is used. The ideal transfer characteristic

for the AD7265 when straight binary coding is output is shown

in Figure 32, and the ideal transfer characteristic for the AD7265

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

VREF range) in Figure 33.

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.

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

VREF ± VREF Input Range

DIGITAL INPUTS

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

Maximum Ratings section for more information. Another

advantage of the SCLK, RANGE, A0 to A2, and CS pins not

being restricted by the VDD + 0.3 V limit is that power supply

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

applied before VDD, 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 VDD.

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 VDD of 5 V, the VDRIVE pin

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 × VREF input range, with a VDD

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

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