AD7262BSTZ datasheet(16/32 Pages) AD

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AD7262

Rev. 0 | Page 16 of 32

The two diodes provide ESD protection. Care must be taken to

ensure that the analog input signals never exceed the supply rails

by more than 300 mV. Exceeding 300 mV causes these diodes to

become forward-biased and to start conducting current into the

substrate. These diodes can conduct up to 10 mA without

causing irreversible damage to the part. The C1 capacitors in

Figure 24 are typically 5 pF and can primarily be attributed to

pin capacitance.

VIN–

VDD

VIN+

VOUT–

VOUT+

VDD

AMP

Figure 24. Analog Input Structure

The AD7262/AD7262-5 can accept differential analog inputs from

⎟

⎠

⎞

⎜

⎝

⎛

−

Gain

REF

⎟

⎠

⎞

⎜

⎝

⎛

Gain

REF

Table 5 details the analog input range for the AD7262/AD7262-5

for the various PGA gain settings. Here, VREF = 2.5 V and VCM =

2.5 V (AVCC/2, with AVCC = 5 V).

Table 5. Analog Input Range for Various PGA Gain Settings

PGA Gain Setting

Analog Input Range for VIN+ and VIN−

0.75 V to 3.25 V1

1.875 V to 3.125 V

2.083 V to 2.916 V

2.187 V to 2.813 V

2.292 V to 2.708 V

2.344 V to 2.656 V

2.396 V to 2.604 V

2.422 V to 2.578 V

2.448 V to 2.552 V

2.461 V to 2.539 V

2.474 V to 2.526 V

2.480 V to 2.520 V

2.487 V to 2.513 V

128

2.490 V to 2.510 V

1 For VCM = 2 V. If VCM = AVCC /2, the analog input range for VIN+ and VIN− is 1.6 V

to 3.4 V.

When a full-scale step input is applied to either differential input

on the AD7262/AD7262-5 while the other analog input is held

at a constant voltage, 3 μs of settling time is typically required

prior to capturing a stable digital output code.

Transfer Function

The AD7262/AD7262-5 output is twos complement, and the

ideal transfer characteristic is shown in Figure 25. The designed

code transitions occur at successive integer LSB values (that is,

1 LSB, 2 LSB, and so on). The LSB size is dependent on the analog

input range selected. The LSB size for the AD7262/AD7262-5 is

shown in the following equation:

⎟⎟

⎟

⎠

⎞

⎜⎜

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

⎟

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⎞

⎜

⎝

⎛

4096

Gain

REF

100...000

011...111

100...001

100...010

011...110

000...001

111...111

000...000

ANALOG INPUT

NOTES

1. FULL-SCALE RANGE (FSR) = VIN+ – VIN–.

(VCM + (FSR/2)) – 1LSB

(VCM – (FSR/2)) + 1LSB

Figure 25. Twos Complement Transfer Function

VDRIVE

The AD7262/AD7262-5 have a VDRIVE feature to control the

voltage at which the serial interface operates. VDRIVE allows the

ADC and the comparators to easily interface to both 3 V and

5 V processors. For example, when the AD7262/AD7262-5 are

operated with AVCC = 5 V, the VDRIVE pin can be powered from

a 3 V supply, allowing a large analog input range with low voltage

digital processors.

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