REV. 0

AD7398/AD7399

–15–

GND

WINDOW 1

WINDOW 2

WINDOW 3

Figure 15. Overlapping Windows Range

The nonoverlapping circuit employs one AD7398/AD7399 and

ten comparators to achieve five voltage windows. These windows

Similarly, the overlapping circuit employs six comparators to

achieve three overlapping windows, Figure 15.

PROGRAMMABLE DAC REFERENCE VOLTAGE

With AD7398/AD7399’s flexibility, one of the internal DACs

rest of the DACs.

The circuit configuration is shown in Figure 16. The relation-

the ratio of R1 and R2, and is given by:

VV

R

R

V

DR

R

REFX

REF

REFX

N

=× +









××

1

2

12

2

1

–

(5)

V

V

R

R

DR

R

REFX

REF

N

=

×+









+×









1

2

1

1

2

2

1

(6)

Where D = Decimal Equivalent of Input Code

N = Number of Bits

R1, R2

Digital Code

R1 = R2

0000 0000 0000

R1 = R2

1000 0000 0000

R1 = R2

1111 1111 1111

R1 = 3R2

0000 0000 0000

R1 = 3R2

1000 0000 0000

R1 = 3R2

1111 1111 1111

R2 and therefore, tight tolerance low tempco thin film resistors

should be used.

APPLICATIONS

STAIRCASE WINDOWS COMPARATOR

Many applications need to determine whether voltage levels are

within predetermined limits. Some requirements are for non-

overlapping windows and others for overlapping windows. Both

circuit configurations are shown in Figures 12 and 13 respectively.

GND

AD7398/

AD7399

WINDOW 1

10k

V+

AD8564

AD8564

1/2 AD8564

WINDOW 2

10k

V+

WINDOW 3

10k

WINDOW 4

10k

WINDOW 5

10k

V+

V+

V+

Figure 12. Nonoverlapping Windows Comparator

GND

WINDOW 1

WINDOW 2

WINDOW 3

WINDOW 4

WINDOW 5

Figure 13. Nonoverlapping Windows Range

GND

AD7398/

AD7399

1/2 AD8564

10k

V+

WINDOW 1

10k

V+

AD8564

WINDOW 2

10k

V+

WINDOW 3

Figure 14. Overlapping Windows Comparator