Data Sheet

AD7908/AD7918/AD7928

Rev. E | Page 11 of 28

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

1

AD7908/

AD7918/

AD7928

TOP VIEW

(Not to Scale)

SCLK

20

2

DIN

19

3

CS

DOUT

18

4

AGND

AGND

AGND

AGND

17

5

16

6

15

7

14

8

13

9

12

10

11

Figure 3. Pin Configuration

Table 6. Pin Function Descriptions

Pin No.

Mnemonic

Description

1

SCLK

Serial Clock. Logic input. SCLK provides the serial clock for accessing data from the part. This clock input is also

used as the clock source for the conversion process of the AD7908/AD7918/AD7928.

2

DIN

Data In. Logic input. Data to be written to the control register of the AD7908/AD7918/AD7928 is provided on

this input and is clocked into the register on the falling edge of SCLK (see the Control Register section).

3

CS

Chip Select. Active low logic input. This input provides the dual function of initiating conversions on the

AD7908/AD7918/AD7928, and also frames the serial data transfer.

4, 8, 17, 20

AGND

Analog Ground. This is the ground reference point for all analog circuitry on the AD7908/AD7918/AD7928. All

analog input signals and any external reference signal should be referred to this AGND voltage. All AGND pins

should be connected together.

5, 6

7

Reference Input for the AD7908/AD7918/AD7928. An external reference must be applied to this input. The

voltage range for the external reference is 2.5 V ± 1% for specified performance.

16 to 9

Analog Input 0 through Analog Input 7. These are eight single-ended analog input channels that are

multiplexed into the on-chip track-and-hold. The analog input channel to be converted is selected by using

Address Bit ADD2 through Address Bit ADD0 of the control register. The address bits, in conjunction with the

SEQ and SHADOW bits, allow the sequencer to be programmed. The input range for all input channels can

input channels must be connected to AGND to avoid noise pickup.

18

DOUT

Data Out. Logic output. The conversion result from the AD7908/AD7918/AD7928 is provided on this output as a

serial data stream. The bits are clocked out on the falling edge of the SCLK input. The data stream from the

AD7908 consists of one leading zero, three address bits indicating which channel the conversion result

corresponds to, followed by the eight bits of conversion data, followed by four trailing zeros, provided MSB

first; the data stream from the AD7918 consists of one leading zero, three address bits indicating which

channel the conversion result corresponds to, followed by the 10 bits of conversion data, followed by two

trailing zeros, also provided MSB first; the data stream from the AD7928 consists of one leading zero, three

address bits indicating which channel the conversion result corresponds to, followed by the 12 bits of

conversion data, provided MSB first. The output coding can be selected as straight binary or twos complement

via the CODING bit in the control register.

19

Logic Power Supply Input. The voltage supplied at this pin determines at what voltage the serial interface of

the AD7908/AD7918/AD7928 operates.