AD7785

Rev. 0 | Page 9 of 32

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

CLK

CS

IOUT1

AIN2(+)

AIN1(–)

AIN1(+)

SCLK

DOUT/RDY

REFIN(–)/AIN3(–)

AIN2(–)

REFIN(+)/AIN3(+)

IOUT2

GND

DIN

AD7785

TOP VIEW

(Not to Scale)

Figure 5. Pin Configuration

Table 4. Pin Function Descriptions

Pin No.

Mnemonic

Description

1

SCLK

Serial Clock Input. This serial clock input is for data transfers to and from the ADC. The SCLK has a Schmitt-

triggered input, making the interface suitable for opto-isolated applications. The serial clock can be

continuous with all data transmitted in a continuous train of pulses. Alternatively, it can be a noncontinuous

clock with the information being transmitted to or from the ADC in smaller batches of data.

2

CLK

Clock In/Clock Out. The internal clock can be made available at this pin. Alternatively, the internal clock can

be disabled, and the ADC can be driven by an external clock. This allows several ADCs to be driven from a

common clock, allowing simultaneous conversions to be performed.

3

CS

Chip Select Input. This is an active low logic input used to select the ADC. CS can be used to select the ADC

in systems with more than one device on the serial bus or as a frame synchronization signal in communicating

with the device. CS can be hardwired low, allowing the ADC to operate in 3-wire mode with SCLK, DIN, and

DOUT used to interface with the device.

4

IOUT1

Output of Internal Excitation Current Source. The internal excitation current source can be made available at

this pin. The excitation current source is programmable so that the current can be 10 μA, 210 μA, or 1 mA.

Either IEXC1 or IEXC2 can be switched to this output.

5

AIN1(+)

Analog Input. AIN1(+) is the positive terminal of the differential analog input pair AIN1(+)/AIN1(

−).

6

AIN1(

−)

Analog Input. AIN1(

−) is the negative terminal of the differential analog input pair AIN1(+)/AIN1(−).

7

AIN2(+)

Analog Input. AIN2(+) is the positive terminal of the differential analog input pair AIN2(+)/AIN2(

−).

8

AIN2(

−)

Analog Input. AIN2(

−) is the negative terminal of the differential analog input pair AIN2(+)/AIN2(−).

9

REFIN(+)/AIN3(+)

Positive Reference Input/Analog Input. An external reference can be applied between REFIN(+) and

REFIN(

REFIN(+)

pin can function as AIN3(+) where AIN3(+) is the positive terminal of the differential analog input pair

AIN3(+)/AIN3(

−).

10

REFIN(

−)/AIN3(−)

Negative Reference Input/Analog Input. REFIN(

−) is the negative reference input for REFIN. This reference

− 0.1 V. This pin also functions as AIN3(−), which is the

negative terminal of the differential analog input pair AIN3(+)/AIN3(

−).

11

IOUT2

Output of Internal Excitation Current Source. The internal excitation current source can be made available at

this pin. The excitation current source is programmable so that the current can be 10 μA, 210 μA, or 1 mA.

Either IEXC1 or IEXC2 can be switched to this output.

12

GND

Ground Reference Point.

13

Supply Voltage, 2.7 V to 5.25 V.

14

Digital Interface Supply Voltage. The logic levels for the serial interface pins are related to this supply, which