5-25

Power Supply Sequencing

Because of the nature of the CMOS process used to

fabricate the ICL7104, and the multiple power supplies

used, there are certain conditions of these supplies under

which a disabling and potentially damaging SCR action can

occur. All of these conditions involve the V+ supply (Norm

+5V) being more positive than the V++ supply. If there is

any possibility of this occurring during start-up, shut down,

under transient conditions during operation, or when insert-

ing a PC board into a “hot” socket, etc., a diode should be

placed between V+ and V++ to prevent it. A germanium or

Schottky rectifier diode would be best, but in most cases a

silicon rectifier is adequate.

Analog and Digital Grounds

Extreme care must be taken to avoid ground loops in the

layout of ICL8068 or ICL8052/7104 circuits, especially in

16-bit and high sensitivity circuits. It is most important that

return currents from digital loads are not fed into the analog

ground line. A recommended connection sequence for the

ground lines is shown in Figure 16.

Application Notes

Some application notes that may be found useful are listed

here:

NOTE #

DESCRIPTION

AnswerFAX

DOC. #

AN016

“Selecting A/D Converters”, by Dave

Fullagar

9016

AN017

“The Integrating A/D Converter”, by Lee

Evans

9017

AN018

“Do’s and Don’ts of Applying A/D

Converters,” by Peter Bradshaw and Skip

Osgood

9018

AN030

“Building a Battery-Operated Auto

Ranging DVM with the ICL7106”

9030

FIGURE 16. GROUNDING SEQUENCE

DEVICE PIN

DIG GND

ICL7104

PIN 2

DIGITAL

LOGIC

I/P

+

-

FILTER

CAP

8068 PIN 2

COMP

PIN 35

ICL7104

AN GND

BUFF

-IN

(IF USED)

REF

VOLTAGE

BUFF

OUT

EXTERNAL

REFERENCE

(IF USED)

PIN 35

ICL7104

AN GND

+15V

-15V

+5V SUPPLY BYPASS CAPACITOR(S)

SUPPLY

RETURN

BOARD

EDGE

ICL8052/ICL7104, ICL8068/ICL7104