AD7762SLASH datasheet(16/23 Pages) AD

16 / 23 page

Data Sheet

AD7767

THEORY OF OPERATION

analog.com

Rev. D | 16 of 23

Figure 32. AD7767 Digital Filter Frequency Response

Figure 33. AD7767-1 Digital Filter Frequency Response

Figure 34. AD7767-2 Digital Filter Frequency Response

ANALOG INPUT STRUCTURE

The AD7767/AD7767-1/AD7767-2 are configured as a differential

input structure. A true differential signal is sampled between the

analog inputs VIN+ and VIN−, Pin 4 and Pin 5, respectively. Using

differential inputs provides rejection of signals that are common to

both the VIN+ and VIN− pins.

Figure 35 shows the equivalent analog input circuit of the AD7767/

AD7767-1/AD7767-2. The two diodes on each of the differential

inputs provide ESD protection for the analog inputs.

Figure 35. Equivalent Analog Input Structure

Take care to ensure that the analog input signal does not exceed

the reference supply voltage (VREF+) by more than 0.3 V, as speci-

fied in the Absolute Maximum Ratings section. If the input voltage

exceeds this limit, the diodes become forward biased and start to

conduct current. The diodes can handle 130 mA maximum.

The impedance of the analog inputs can be modeled as a parallel

combination of C1 and the network formed by the series connection

of RIN, C1, and C2. The value of C1 is dominated by the pin

capacitance. RIN is typically 1.4 kΩ, the lumped component of serial

resistors and the RON of the switches. C2 is typically 22 pF, and its

value is dominated by the sampling capacitor.

SUPPLY AND REFERENCE VOLTAGES

The AD7767/AD7767-1/AD7767-2 operate from a 2.5 V supply

applied to the DVDD and AVDD pins. The interface is specified to op-

erate between 1.7 V and 3.6 V. The AD7767/AD7767-1/ AD7767-2

operate from a reference input in the range of 2.2 V to 2 × AVDD ap-

plied to the VREF+ pin. The nominal reference supply voltage is 5 V,

but a 2.5 V supply can also be used. When using a 5 V reference,

the recommended reference devices are the ADR445, ADR435, or

ADR425; when using 2.5 V, the ADR441, ADR431, or ADR421 are

recommended. The voltage applied to the reference input (VREF+)

operates both as a reference supply and as a power supply to

the AD7767/AD7767-1/AD7767-2 device. Therefore, when using a

5 V reference input, the full-scale differential input range of the

AD7767/AD7767-1/AD7767-2 is 10 V. See the Driving the AD7767

section for details on the maximum input voltage.

AD7762/ Datasheet(PDF) 16 Page - Analog Devices

AD7762/ Datasheet(HTML) 16 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Datasheet Download

Link URL