Datasheet

AD5280/AD5282
Rev. C | Page 17 of 28
READBACK RDAC VALUE
The AD5280/AD5282 allow the user to read back the RDAC
values in read mode. However, for the dual-channel AD5282,
the channel of interest is the one that is previously selected in
the write mode. When users need to read the RDAC values of
both channels in the AD5282, they can program the first
subaddress in write mode and then change to read mode to read
the first channel value. After that, they can change back to write
mode with the second subaddress and read the second channel
value in read mode again. It is not necessary for users to issue
the Frame 3 data byte in write mode for subsequent readback
operation. Users should refer to Figure 45 and Figure 46 for the
programming format.
ADDITIONAL PROGRAMMABLE LOGIC OUTPUT
The AD5280/AD5282 feature additional programmable logic
outputs, O
1
and O
2
, which can be used to drive a digital load,
analog switches, and logic gates. O
1
and O
2
default to Logic 0. The
logic states of O
1
and O
2
can be programmed in Frame 2 under
write mode (see Figure 45). These logic outputs have adequate
current driving capability to sink/source milliamperes of load.
Users can also activate O
1
and O
2
in three ways without
affecting the wiper settings by programming as follows:
• Perform start, slave address, acknowledge, and instruction
bytes with O
1
and O
2
specified, acknowledge, stop.
• Complete the write cycle with stop, then start, slave address
byte, acknowledge, instruction byte with O
1
and O
2
specified, acknowledge, stop.
• Not complete the write cycle by not issuing the stop, then
start, slave address byte, acknowledge, instruction byte
with O
1
and O
2
specified, acknowledge, stop.
SELF-CONTAINED SHUTDOWN FUNCTION AND
PROGRAMMABLE PRESET
Shutdown can be activated by strobing the
SHDN
pin or
programming the SD bit in the write mode instruction byte.
As shown in , when shutdown is asserted, the
AD5280/AD5282 open SW
A
to let the A terminal float and
short the W terminal to the B terminal. The AD5280/AD5282
consume negligible power during shutdown mode, resuming
the previous setting once the
Figure 44
SHDN
pin is released.
In addition, shutdown can be implemented with the device
digital output as shown in Figure 47. In this configuration, the
device is shut down during power-up, but the user is allowed to
program the device at any preset levels. When it is done, the
user programs O
1
high with the valid coding and the device
exits from shutdown and responds to the new setting. This self-
contained shutdown function allows absolute shutdown during
power-up, which is crucial in hazardous environments, without
adding extra components. Also, the sleep mode programming
feature during shutdown allows the AD5280/AD5282 to have a
programmable preset at any level, a solution that can be as
effective as using other high cost EEPROM devices. Because of
the extra power drawn on R
PD
, note that a high value should be
chosen for the R
PD
.
SDA
SHDN
SCL
R
PD
O
1
02929-046
Figure 47. Shutdown by Internal Logic Output
MULTIPLE DEVICES ON ONE BUS
Figure 48 shows four AD5282 devices on the same serial bus.
Each has a different slave address because the states of their Pin
AD0 and Pin AD1 are different. This allows each RDAC within
each device to be written to or read from independently. The
master device output bus line drivers are open-drain pull-
downs in a fully I
2
C-compatible interface.
SDA
SCL
R
P
R
P
5V 5V 5V
MASTER
5V
SDA
AD1
AD0
AD5282
SCL SDA
AD1
AD0
AD5282
SCL SDA
AD1
AD0
AD5282
SCL SDA
AD1
AD0
AD5282
SCL
02929-047
Figure 48. Multiple AD5282 Devices on One Bus