CAT525(2001) 查看數據表（PDF） - Catalyst Semiconductor => Onsemi

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CAT525
(Rev.:2001)

Configured Digitally Programmable Potentiometer (DPP™): Programmable Voltage Applications

Catalyst Semiconductor => Onsemi 

CAT525

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 CAT525 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 four DACs in any order or sequence. The

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

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

output values stored in EEPROM memory.

Figure 3. Temporary Change in Output

to 1 2 3 4 5 6 7 8 9 10 11 12

N N+1 N+2

CS

DI

DO

PROG

RDY/BSY

DAC

OUTPUT

NEW DAC DATA

1 A0 A1 D0 D1 D2 D3 D4 D5 D6 D7

CURRENT DAC DATA

D0 D1 D2 D3 D4 D5 D6 D7

CURRENT

DAC VALUE

NON-VOLATILE

NEW

DAC VALUE

VOLATILE

CURRENT

DAC VALUE

NON-VOLATILE

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 CAT525’s internal control circuitry discards

from the programming register the new data two clock

cycles after receiving it if no PROG signal is received.

APPLICATION CIRCUITS

+5V

Vi

CONTROL

& DATA

VDD

VREFH

OCPATT552055

GND

VREFL

RI

RF

+15V

–

+ OP 07

-15V

V OUT

VOUT = VDAC (RI+ RF) -VI RF

RI

For RI = RF

VOUT = 2VDAC-VI

DAC INPUT

DAC OUTPUT

MSB LSB

1111 1111

VDAC

=

—CO—D—E

255

(VFS- VZERO ) + VZERO

VFS = 0.99 VREF

VZERO = 0.01 VREF

—2255—55 (.98 VREF ) + .01 VREF = .990 VREF

ANALOG

OUTPUT

VREF = 5V

R I = RF

VOUT = +4.90V

1000 0000

0111 1111

0000 0001

—1225—85 (.98 VREF) + .01 VREF = .502 VREF

—1225—75 (.98 VREF) + .01 VREF = .498 VREF

—215—5 (.98 VREF) + .01 VREF = .014 VREF

VOUT = +0.02V

VOUT = -0.02V

VOUT = -4.86V

0000 0000 —205—5 (.98 VREF) + .01 VREF = .010 VREF

VOUT = -4.90V

Bipolar DAC Output

+5V

RI

RF

CONTROL

& DATA

VDD

VREFH

+15V

–

COAPT552055

+ OP 07

GND

VREFL

-15V

VOUT

=

(1

+

–R–F–)

RI

VDAC

Amplified DAC Output

V OUT

7

Doc. No. 25078-00 4/01 - A M-1

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