Datasheet

AD5360/AD5361
Rev. A | Page 19 of 28
RESET FUNCTION
The reset function is initiated by the
RESET
pin. On the rising
edge of
RESET
, the AD5360/AD5361 state machine initiates a
reset sequence to reset the X, M, and C registers to their default
values. This sequence typically takes 300 μs, and the user should
not write to the part during this time. On power-up, it is recom-
mended that the user bring
RESET
high as soon as possible to
properly initialize the registers.
When the reset sequence is complete (and provided that
CLR
is
high), the DAC output is at a potential specified by the default
register settings, which are equivalent to SIGGNDx. The DAC
outputs remain at SIGGNDx until the X, M, or C register is
updated and
LDAC
is taken low. The AD5360/AD5361 can be
returned to the default state by pulsing
RESET
low for at least
30 ns. Note that, because the reset function is rising edge trig-
gered, bringing
RESET
low has no effect on the operation of
the AD5360/AD5361.
CLEAR FUNCTION
CLR
is an active low input that should be high for normal
operation. The
CLR
pin has an internal 500 kΩ pull-down
resistor. When
CLR
is low, the input to each of the DAC output
buffer stages (VOUT0 to VOUT15) is switched to the externally
set potential on the relevant SIGGNDx pin. While
CLR
is low,
all
LDAC
pulses are ignored. When
CLR
is taken high again, the
DAC outputs return to their previous values. The contents of
input registers and DAC Register 0 to DAC Register 15 are not
affected by taking
CLR
low. To prevent glitches appearing on
the outputs,
CLR
should be brought low whenever the output
span is adjusted by writing to the offset DAC.
BUSY AND LDAC FUNCTIONS
The value of an X2 (A or B) register is calculated each time the
user writes new data to the corresponding X1, C, or M register.
During the calculation of X2, the
BUSY
output goes low. While
BUSY
is low, the user can continue writing new data to the X1,
M, or C register (see the Register Update Rates section for more
details), but no DAC output updates can take place.
The
BUSY
pin is bidirectional and has a 50 kΩ internal pull-up
resistor. When multiple AD5360 or AD5361 devices may be
used in one system, the
BUSY
pins can be tied together. This is
useful when it is required that no DAC in any device be updated
until all other DACs are ready. When each device has finished
updating the X2 (A or B) register, it releases the
BUSY
pin. If
another device has not finished updating its X2 registers, it
holds
BUSY
low, thus delaying the effect of
LDAC
going low.
The DAC outputs are updated by taking the
LDAC
input low. If
LDAC
goes low while
BUSY
is active, the
LDAC
event is stored
and the DAC outputs update immediately after
BUSY
goes
high. A user can also hold the
LDAC
input permanently low. In
this case, the DAC outputs update immediately after
BUSY
goes
high. Whenever the
A
/B select registers are written to,
BUSY
also goes low, for approximately 600 ns.
The AD5360/AD5361 have flexible addressing that allows
writing of data to a single channel, all channels in a group, the
same channel in Group 0 and Group 1, or all channels in the
device. This means that 1, 2, 8, or 16 DAC register values may
need to be calculated and updated. Because there is only one
multiplier shared among 16 channels, this task must be done
sequentially, so the length of the
BUSY
pulse varies according to
the number of channels being updated.
Table 8.
BUSY
Pulse Widths
Action
BUSY
Pulse Width
1
Loading Input, C, or M to 1 Channel
2
1.5 μs maximum
Loading Input, C, or M to 2 Channels 2.1 μs maximum
Loading Input, C, or M to 8 Channels 5.7 μs maximum
Loading Input, C, or M to 16 Channels 10.5 μs maximum
1
BUSY
pulse width = ((number of channels + 1) × 600 ns) + 300 ns.
2
A single channel update is typically 1 μs.
The AD5360/AD5361 contain an extra feature whereby a DAC
register is not updated unless its X2A or X2B register has been
written to since the last time
LDAC
was brought low. Normally,
when
LDAC
is brought low, the DAC registers are filled with
the contents of the X2A or X2B registers, depending on the
setting of the
A
/B select register. However, the AD5360/
AD5361 update the DAC register only if the X2A or X2B data has
changed, thereby removing unnecessary digital crosstalk.
BIN/2SCOMP PIN
The
BIN
/2SCOMP pin determines if the output data is presented
as offset binary or twos complement. If this pin is low, the data
is straight binary. If it is high, the data is twos complement. This
affects only the X, C, and offset DAC registers; the M register
and the control and command data are interpreted as straight
binary.
TEMPERATURE SENSOR
The on-chip temperature sensor provides a voltage output
at the TEMP_OUT pin that is linearly proportional to the
Centigrade temperature scale. The typical accuracy of the
temperature sensor is ±1°C at +25°C and ±5°C over the −40°C
to +85°C range. Its nominal output voltage is 1.46 V at +25°C,
varying at 4.4 mV/°C. Its low output impedance, low self-
heating, and linear output simplify interfacing to temperature
control circuitry and analog-to-digital converters.