Datasheet

Data Sheet AD5697R
Rev. 0 | Page 23 of 28
HARDWARE RESET (
RESET
)
RESET
is an active low reset that allows the outputs to be
cleared to either zero scale or midscale. The clear code value is
user selectable via the power-on reset select (RSTSEL) pin. It is
necessary to keep
RESET
low for a minimum amount of time
to complete the operation . When the
RESET
signal is returned
high, the output remains at the cleared value until a new value
is programmed. The outputs cannot be updated with a new
value while the
RESET
pin is low. Also, a software executable
reset function can reset the DAC to the power-on reset code.
Command 0110 is designated for this software reset function
(see
Table 7). Any events on
LDAC
or
RESET
during power-on
reset are ignored.
RESET SELECT PIN (RSTSEL)
The AD5697R contains a power-on reset circuit that controls the
output voltage during power-up. By connecting the RSTSEL pin
low, the output powers up to zero scale. Note that this is outside
the linear region of the DAC; by connecting the RSTSEL pin
high, V
OUT
powers up to midscale. The output remains powered
up at this level until a valid write sequence is made to the DAC.
INTERNAL REFERENCE SETUP
Command 0111 is reserved for setting up the internal reference
(see Table 7). By default, the on-chip reference is on at power-up.
To reduce the supply current, this reference can be turned off by
setting the software-programmable bit, DB0, as shown in Table 16.
Table 15 shows how the state of the bit corresponds to the mode
of operation.
Table 15. Reference Setup Register
Internal Reference Setup Register (DB0) Action
0 Reference on (default)
1
Reference off
SOLDER HEAT REFLOW
As with all IC reference voltage circuits, the reference value
experiences a shift induced by the soldering process. Analog
Devices, Inc., performs a reliability test called precondition to
mimic the effect of soldering a device to a board. The output
voltage specification quoted in Table 2 includes the effect of this
reliability test.
Figure 48 shows the effect of solder heat reflow (SHR) as measured
through the reliability test (precondition).
Figure 48. SHR Reference Voltage Shift
LONG-TERM TEMPERATURE DRIFT
Figure 49 shows the change in V
REF
value after 1000 hours in life
test at 150°C.
Figure 49. Reference Drift Through to 1000 Hours
Table 16. 24-Bit Input Shift Register Contents for Internal Reference Setup Command
1
DB23 (MSB) DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 to DB1 DB0 (LSB)
0 1 1 1 X X X X X 0/1
Command bits (C3 to C0) Address bits (A3 to A0) Don’t care Reference setup register
1
X = don’t care.
60
0
10
20
30
40
50
2.498 2.499 2.500 2.501 2.502
HITS
V
REF
(V)
POSTSOLDER
HEAT REFLOW
PRESOLDER
HEAT REFLOW
11253-049
60
0
10
20
30
40
50
2.498 2.499 2.500 2.501 2.502
HITS
V
REF
(V)
0 HOUR
168 HOURS
500 HOURS
1000 HOURS
11253-050