Datasheet
AD5590
Rev. A | Page 31 of 44
DSYNC
Interrupt
In a normal write sequence, the
DSYNCx
line is kept low for
32 falling edges of DSCLK, and the DAC is updated on the 32
nd
falling edge and rising edge of
DSYNCx
. However, if
DSYNCx
is
brought high before the 32
nd
falling edge, this acts as an interrupt
to the write sequence. The shift register is reset, and the write
sequence is seen as invalid. Neither an update of the DAC
register contents nor a change in the operating mode occurs
(see Figure 63).
DAC Internal Reference Register
The on-board references in the DAC blocks are off at power-up
by default. This allows the use of an external reference if the
application requires it. The on-board references can be turned
on or off by a user-programmable internal REF register by
setting Bit DB0 high or low (see Table 13). Command 1000 is
reserved for setting the internal REF register (see Table 11).
DAC Power-On Reset
The DAC blocks contain a power-on reset circuit that controls
the output voltage during power-up. The DAC outputs power
up to 0 V. The output remains powered up at this level until a
valid write sequence is made to the DAC. This is useful in appli-
cations where it is important to know the state of the output of
the DAC while it is in the process of powering up. There is also
a software executable reset function that resets the DAC to the
power-on reset code. Command 0111 is reserved for this reset
function (see Table 11). Any events on
LDAC
or
CLR
during
power-on reset are ignored.
DAC Power-Down Modes
The DAC block contains four separate modes of operation.
Command 0100 is reserved for the power-down function (see
Table 11). These modes are software-programmable by setting
Bit DB9 and Bit DB8 in the control register.
Table 15 shows how the state of the bits corresponds to the mode
of operation of the device. Any or all DACs (DAC0 to DAC7 in
Block 1 or DAC8 to DAC15 in Block 2) can be powered down to
the selected mode by setting the corresponding eight bits to 1. See
Table 16 for the contents of the input shift register during power-
down/power-up operation. When using the internal reference,
only all channel power-down to the selected modes is supported.
When both bits are set to 0, each block works normally with its
normal power consumption of 1.3 mA at 5 V. However, for the
three power-down modes, the supply current of each block falls
to 0.4 µA at 5 V. Not only does the supply current fall, but the
output stage is also internally switched from the output of the
amplifier to a resistor network of known values. This has the
advantage that the output impedance of the DAC is known
while it is in power-down mode. There are three different
options. The output is connected internally to GND through
either a 1 kΩ or a 100 kΩ resistor, or it is left open-circuited
(three-state). The output stage is illustrated in Figure 62.
RESISTOR
NETWORK
V
OUT
RESISTOR
STRING DAC
POWER-DOWN
CIRCUITRY
AMPLIFIER
07691-063
Figure 62. Output Stage During Power-Down
DSCLK
DDIN
DB31 DB0
INVALID WRITE SEQUENCE:
SYNC HIGH BEFORE 32ND FALLING EDGE
VALID WRITE SEQUENCE, OUTPUT UPDATES
ON THE 32ND FALLING EDGE
DB31 DB0
DSYNCx
07691-062
Figure 63.
SYNC
Interrupt Facility
Table 13. DAC Internal Reference Register
Internal REF Register (DB0) Action
0 Reference off (default)
1 Reference on
Table 14. DAC 32-Bit Input Shift Register Contents for Reference Setup Command
MSB
LSB
DB31 to DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 to DB1 DB0
X 1 0 0 0 X X X X X 1/0
Don’t care
Command bits (C3 to C0)
Address bits (A3 to A0)—don’t care
Don’t care
Internal REF register