CAT514 Datasheet, PDF (7/11 Pages) Catalyst Semiconductor – 8-Bit Quad Digital POT

CAT514
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 CAT514 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.
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 CAT514’s internal control circuitry discards
the new data from the programming register two clock
cycles after receiving it (after reception is complete) if no
PROG signal is received.
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
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
APPLICATION CIRCUITS
+5V
CONTROL
& DATA
VDD
VREFH
OCPATT50144
GND
VREFL
+15V
–
+ _{OP 07}
-15V
V _OUT
VOUT = VDAC
Buffered DAC Output
CONTROL
& DATA
+5V
VDD
VREFH
OCPATT551044
GND
VREFL
Ri
RF
+15V
–
+ _{OP 07}
V _OUT
-15V
VOUT = (1 + –^RR–^FI–) VDAC
Amplified DAC Output
CONTROL
& DATA
+5V
Vi
VDD
VREFH
OCPAT T550144
GND
VREFL
Ri
RF
+15V
–
+ _{OP 07}
-15V
VOUT
VOUT = VDAC (Ri+ RF) -Vi RF
Ri
For Ri = RF
VOUT = 2VDAC-Vi
DAC INPUT
DAC OUTPUT
MSB LSB
1111 1111
VDAC= —^C2O—_5D5—^E (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
—₂₅₁—₅ (.98 VREF) + .01 VREF = .014 VREF
VOUT = +0.02V
VOUT = -0.02V
VOUT = -4.86V
0000 0000 —₂₅₀—₅ (.98 VREF) + .01 VREF = .010 VREF
VOUT = -4.90V
Bipolar DAC Output
7
Doc. No. 25075-00 2/98 M-1