AD7769

–6–

REV. A

PIN FUNCTION DESCRIPTION

Pin

Mnemonic

Description

+12 V Power Supply. This powers the analog circuitry.

+5 V Power Supply. This powers the logic circuitry.

3–10

DB7–DB0

Input/Output Data Bus. A bidirectional data port from which ADC output data may be read

and to which DAC input data may be written. DB7 is the Most Significant Bit.

11

INT

Interrupt Output (active low).

INT is set high on the falling edge of RD or WR to the ADC

and goes low at the end of a conversion.

12

CLK

Clock input. A clock is required for the ADC. An external TTL-compatible clock may be applied to

external clock, the mark-space ratio can vary from 30/70 to 70/30.

13

CHA/CHB

Channel A/Channel B Select Input. Selects Channel A or Channel B of the DAC or ADC.

Used in conjunction with

WR, RD, CS and ADC/DAC for read or write operations.

14

DGND

Digital Ground.

15

ADC/DAC

ADC or DAC Select Input. Selects either the ADC or the DAC for read or write operations in

conjunction with

WR, RD, CS and CHA/CHB.

16

WR

Write Input (edge triggered). This is used in conjunction with the

ADC/DAC, CHA/CHB and CS

control inputs to start an ADC conversion or write data to the DAC. An ADC conversion starts on the

rising edge of

WR.

17

RD

Read Input (active low). This input must be low to access data from the ADC.

18

CS

Chip Select Input (active low). The device is selected when this input is low.

19

ADC Reference Input. The voltage applied to this pin with respect to AGND (ADC) sets the

20

AGND (ADC)

ADC Analog Ground.

21

22

ADC Reference Input. The voltage applied to this pin with respect to AGND (ADC) sets the

midpoint of the ADC transfer function.

23

Analog Input for Channel A. The input voltage range of both ADC channels is given by:

±V

24

AGND (DAC)

DAC Analog Ground.

25

DAC Reference Input. The voltage applied to this pin with respect to AGND (DAC) sets the

26

27

DAC Reference Input. The voltage applied to this pin with respect to AGND (DAC) sets the

midpoint output voltage of the DACs.

28

Analog Output Voltage from DAC A. The output voltage range of both DACs is given by:

TERMINOLOGY

Relative Accuracy

For an ADC, Relative Accuracy or endpoint nonlinearity is the

maximum deviation, in LSBs, of the ADC’s actual code transi-

tion points from a straight line drawn between the endpoints of

the ADC transfer function, i.e., the 00 to 01 and FE to FF Hex

(01111111 to 11111111 Binary) code transitions.

For a DAC, Relative Accuracy or endpoint nonlinearity is a

measure of the maximum deviation, in LSBs, from a straight

line passing through the endpoints of the DAC transfer func-

tion, i.e., those voltages which correspond to codes 00 and FF

Hex.

For the specified input and output ranges, 1 LSB = 19.5 mV,

Differential Nonlinearity

Differential Nonlinearity is the difference between the measured

change and the ideal 1 LSB change between any two adjacent

codes. A specified differential nonlinearity of

±1 LSB max en-

sures monotonicity (DAC) or no missed codes (ADC).

Bias Offset Error

For an ideal ADC, the output code for an input voltage equal to

Bias Offset Error is the difference between the actual midpoint

For an ideal DAC, the output voltage for code 80 Hex should

expressed in LSBs.