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Data Sheet

AD5697R

Rev. B | Page 23 of 27

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 during a power-on reset are

ignored. If the RESET pin is pulled low at power-up, the device

does not initialize correctly until the pin is released.

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, VOUT 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

Reference on (default)

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 47 shows the effect of solder heat reflow (SHR) as measured

through the reliability test (precondition).

Figure 47. SHR Reference Voltage Shift

LONG-TERM TEMPERATURE DRIFT

Figure 48 shows the change in the VREF (ppm) value after

1000 hours at 25°C ambient temperature.

Figure 48. Reference Drift Through to 1000 Hours

Table 16. 24-Bit Input Shift Register Contents for Internal Reference Setup Command1

DB23 (MSB)

DB22

DB21

DB20

DB19

DB18

DB17

DB16

DB15 to DB1

DB0 (LSB)

0/1

Command bits (C3 to C0)

Address bits (A3 to A0)

Don’t care

Reference setup register

1 X = don’t care.

2.498

2.499

2.500

2.501

2.502

VREF (V)

POSTSOLDER

HEAT REFLOW

PRESOLDER

HEAT REFLOW

ELAPSED TIME (Hours)

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