CAT522

7

8/00

Advanced Information

MSB

LSB

1111

1111

—— (.98 V

) + .01 V

= .990 V

V

= +4.90V

1000

0000

—— (.98 V

) + .01 V

= .502 V

V

= +0.02V

0111

1111

—— (.98 V

) + .01 V

= .498 V

V

= -0.02V

0000

0001

—— (.98 V

) + .01 V

= .014 V

V

= -4.86V

0000

0000

—— (.98 V

) + .01 V

= .010 V

V

= -4.90V

REF

REF

REF

IF

V

= 5V

REF

255

255

OUT

DAC INPUT

DAC OUTPUT

ANALOG

R = R

OUTPUT

REF

REF

REF

OUT

128

255

127

255

REF

REF

REF

OUT

1

255

REF

REF

REF

OUT

REF

REF

REF

OUT

0

255

V

= 0.99 V

FS

REF

V

= 0.01 V

ZERO

REF

V

= ——— (V

- V

) + V

DAC

CODE

255

FS

ZERO

ZERO

Figure 3. Temporary Change in Output

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

D0

D1

D2

D3

D4

D5

D6

D7

1

NEW DAC DATA

CURRENT DAC DATA

DO

DI

CS

PROG

DAC

OUTPUT

t

1

2

3

4

5

6

7

8

9

10

11

12

N

N+1 N+2

o

CURRENT

DAC VALUE

NON-VOLATILE

NEW

DAC VALUE

VOLATILE

CURRENT

DAC VALUE

NON-VOLATILE

RDY/BSY

setting is reloaded into the DAC control register. Since

this value is the same as that which had been there

previously no change in the DAC’s output is noticed.

Had the value held in the control register been different

from that stored in EEPROM then

a change would occur

at the read cycle’s conclusion.

TEMPORARILY CHANGE OUTPUT

The CAT522 allows temporary changes in DAC’s output

to be made without disturbing the settings retained in

EEPROM memory. This feature is particularly useful

when testing for a new output setting and allows for user

adjustment of preset or default values without losing the

original factory settings.

Figure 3 shows the control and data signals needed to

effect a temporary output change. DAC settings may be

changed as many times as required and can be made to

any of the two DACs in any order or sequence. The

temporary setting(s) remain in effect long as CS remains

high. When CS returns low all two DACs will return to the

output values stored in EEPROM memory.

When it is desired to save a new setting acquired using

this feature, the new value must be reloaded into the

DAC control register prior to programming. This is be-

cause the CAT522’s internal control circuitry discards

from the programming register the new data two clock

cycles after receiving it if no PROG signal is received.

Amplified DAC Output

APPLICATION CIRCUITS

Bipolar DAC Output

OPT 505

GND

VDD

V

H

REF

V

L

REF

CONTROL

& DATA

+

–

OP 07

V

=

(

) -V

OUT

RF

R +

I

-15V

+15V

+5V

RR

I

F

RI

I

RF

VDAC

For R =

I

RF

V

= 2V

-V

OUT

I

DAC

Vi

V

OUT

CAT522

OPT 505

GND

VDD

V

H

REF

V

L

REF

CONTROL

& DATA

+

–

OP 07

VOUT

-15V

+15V

+5V

RR

I

F

V

= (1 + –––) V

OUT

DAC

RF

RI

CAT522