Rev. PrC | Page 3 of 13

GENERAL DESCRIPTION

The AD7771 is an 8-channel simultaneously sampled, Analog-

to-Digital Converter. There are 8 full Sigma Delta ADCs on-

chip. The AD7771 provides a high input impedance to allow for

direct sensor connection. Each input channel has a

programmable gain stage catering for gains of 1,2,4,8 to map

lower amplitude sensor outputs into the Full Scale ADC input

range to maximize the Dynamic Range of the signal chain. The

Analog inputs can accept unipolar 0 to 2.4V or true bipolar

±1.25V analog input signals with 3.3V or ±1.65V Analog

Supply voltages respectively. The Analog inputs can be

configured to accept True Differential or Single-Ended signals

to match different sensor output configurations.

Each channel contains an ADC modulator and Sinc 3/Sinc 5

low latency digital filters. A Sample Rate Converter (SRC) is

provided to allow fine resolution control over the AD7771

Output Data Rate (ODR). This can be used in Power Quality

Applications where the ODR resolution is required to maintain

coherency with 0.01Hz changes in the line frequency. The SRC

can be programmed through the SPI interface. The AD7771

implements two different interfaces, Data Output Interface and

a SPI control Interface. The ADC Data Output interface is

dedicated to transmitting the ADC conversion results from the

AD7771 to the processor, acting as a master. The SPI interface

is used to write to and read from the AD7771 configuration

registers and for the control and reading of data from the SAR

ADC. The SPI interface can also be configure to output the

sigma delta conversion data.

The AD7771 includes a 12-Bit SAR ADC. This ADC can be

used for AD7771 diagnostics without having to decommission

one of the Sigma Delta ADC channels dedicated to system

measurement functions. With the use of an external multiplexer

and signal conditioning, the SAR ADC can be used to validate

the Sigma Delta ADC measurements in applications where

Functional Safety is required. In addition, the AD7771 offers

three GPIOs that can be used to control an external multiplexer.

The AD7771 contains a 2.5V reference and reference buffer.

The reference has a temperature co-efficient of 20 ppm/°C max.

The AD7771 offers two modes of operation: High Resolution

Mode and Low Power Mode. The High Resolution mode

provides higher dynamic range while consuming 13 mW/ch

and the Low Power mode consumes just 5 mW/ch at a reduced

dynamic range specification.

The specified operating temperature range is -40°C to +105°C

while the part is operational up to +125°C.

Input referred noise for SINC 3 and SINC5 filters,

SINC5

ODR BW

Gain1(uVrms/uVpp) Gain2(uVrms/uVpp) Gain4(uVrms/uVpp) Gain8(uVrms/uVpp)

128k

26098

30.20

22.80

19.20

17.20

64k

14122

13.70

10.10

8.28

7.46

32k

7215

7.40

4.79

3.63

3.14

16k

3627.5

4.65

2.74

1.87

1.54

8k

1816.2

3.17

1.79

1.17

0.93

4k

908.5

2.23

1.25

0.79

0.63

SINC3

ODR BW

Gain1(uVrms/uVpp) Gain2(uVrms/uVpp) Gain4(uVrms/uVpp) Gain8(uVrms/uVpp)

32k

10045

11.91

7.00

4.79

3.84

16k

5076.2

5.60

3.35

2.37

1.99

8k

2545

3.64

2.10

1.42

1.15

4k

1273.5

2.51

1.42

0.93

0.74

2k

636.75

1.77

0.99

0.64

0.51

1k

318.5

1.25

0.71

0.45

0.36

Preliminary Technical Data

AD7771