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AD5280/AD5282

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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, O1 and O2, which can be used to drive a digital load,

analog switches, and logic gates. O1 and O2 default to Logic 0. The

logic states of O1 and O2 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 O1 and O2 in three ways without

affecting the wiper settings by programming as follows:

•

Perform start, slave address, acknowledge, and instruction

bytes with O1 and O2 specified, acknowledge, stop.

•

Complete the write cycle with stop, then start, slave address

byte, acknowledge, instruction byte with O1 and O2

specified, acknowledge, stop.

•

Not complete the write cycle by not issuing the stop, then

start, slave address byte, acknowledge, instruction byte

with O1 and O2 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 SWA 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 O1 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 RPD, note that a high value should be

chosen for the RPD.

SDA

SHDN

SCL

RPD

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 I2C-compatible interface.

SDA

SCL

MASTER

SDA

AD1

AD0

AD5282

SCL

SDA

AD1

AD0

AD5282

SCL

SDA

AD1

AD0

AD5282

SCL

SDA

AD1

AD0

AD5282

SCL

Figure 48. Multiple AD5282 Devices on One Bus

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