Datasheet

AD5686R/AD5685R/AD5684R Data Sheet
Rev. B | Page 26 of 32
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
RESET
select pin. It is necessary to
keep
RESET
low for a minimum amount of time to complete
the operation (see Figure 2). 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. There is also a software executable
reset function that resets 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 AD5686R/AD5685R/AD5684R contain 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
The on-chip reference is on at power-up by default. To reduce the
supply current, this reference can be turned off by setting
software programmable bit, DB0, in the control register.
Table 14 shows how the state of the bit corresponds to the mode
of operation. Command 0111 is reserved for setting up the
internal reference (see Figure 9). Table 14 shows how the state
of the bits in the input shift register corresponds to the mode of
operation of the device during internal reference setup.
Table 14. 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 previously includes the effect of
this reliability test.
Figure 57 shows the effect of solder heat reflow (SHR) as
measured through the reliability test (precondition).
Figure 57. SHR Reference Voltage Shift
LONG-TERM TEMPERATURE DRIFT
Figure 58 shows the change in V
REF
value after 1000 hours in life
test at 150°C.
Figure 58. Reference Drift Through to 1000 Hours
60
0
10
20
30
40
50
2.498 2.499 2.500 2.501 2.502
HITS
V
REF
(V)
10485-060
POSTSOLDER
HEAT REFLOW
PRESOLDER
HEAT REFLOW
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
10485-061