3-39

In low resolution applications, where the converter uses only

quate. In this application a C of 51pF is recommended and the

resolution) a crystal oscillator is recommended to prevent the

noise from increasing as the input signal is increased due to

frequency jitter of the R-C oscillator. Both R-C and crystal oscil-

lator circuits are shown in Figure 12.

Powering the ICL7129

The ICL7129 may be operated as a battery powered hand-held

instrument or integrated into larger systems that have more

sophisticated power supplies. Figures 13, 14, and 15 show

various powering modes that may be used with the ICL7129.

The standard supply connection using a 9V battery is shown

in the Typical Application Schematic.

The power connection for systems with +5V and -5V sup-

plies available is shown in Figure 13. Notice that measure-

ments are with respect to ground. COMMON is also tied to

INLO to remove any common-mode voltage swing on the

integrator amplifier inputs.

It is important to notice that in Figure 13, digital ground of the

ICL7129 (DGND pin 36) is not directly connected to power

supply ground. DGND is set internally to approximately 5V

less than the V+ terminal and is not intended to be used as a

power input pin. It may be used as the ground reference for

external logic, as shown in Figure 4 and 5. In Figure 4, DGND

is used as the negative supply rail for external logic provided

that the supply current for the external logic does not cause

excessive loading on DGND. The DGND output can be buff-

ered as shown in Figure 5. Here, the logic supply current is

shunted away from the ICL7129 keeping the load on DGND

low. This treatment of the DGND output is necessary to insure

compatibility when the external logic is used to interface

directly with the logic inputs and outputs of the ICL7129.

When a battery voltage between 3.8V and 6V is desired for

operation, a voltage doubling circuit should be used to bring

the voltage on the ICL7129 up to a level within the power sup-

ply voltage range. This operating mode is shown in Figure 14.

Again measurements are made with respect to COMMON

since the entire system is floating. Voltage doubling is

accomplished by using an ICL7660 CMOS voltage converter

and two inexpensive electrolytic capacitors. The same princi-

ple applies in Figure 15 where the ICL7129 is being used in

a system with only a single +5V power supply. Here mea-

surements are made with respect to power supply ground.

ICL7129

2

40

75k

Ω

51pF

1

ICL7129

2

40

27k

Ω

10pF

1

120kHz

5pF

V+

V-

CRYSTAL MODE:

PARALLEL

FIGURE 12. RC AND CRYSTAL OSCILLATOR CIRCUITS

ICL7129

24

34

35

28

33

32

23

36

ICL8089

+5V

-5V

0.1

µF

0.1

µF

0.1

µF

V-

V+

REF HI

REF LO

DGND

COM

IN HI

IN LO

FIGURE 13. POWERING THE ICL7129 FROM +5V AND -5V

ICL7129

24

34

35

28

33

32

23

36

10

µF

V-

V+

+

-

2

4

5

+

10

µF

ICL7660

3

+

8

3.8V TO

6V

+

-

REF HI

REF LO

DGND COM

IN HI

IN LO

FIGURE 14. POWERING THE ICL7129 FROM A 3.8V TO 6V BATTERY

ICL7129

24

34

35

28

33

32

23

36

ICL8089

+5V

10

µF

0.1

µF

0.1

µF

V-

V+

+

-

2

4

5

+

10

µF

ICL7660

3

+

8

FIGURE 15. POWERING THE ICL7129 FROM A SINGLE

POLARITY POWER SUPPLY

ICL7129