AD5280BRU200 查看數據表（PDF） - Analog Devices
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AD5280BRU200 Datasheet PDF : 20 Pages
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AD5280/AD5282
READBACK RDAC VALUE
AD5280/AD5282 allows the user to read back the RDAC values
in the Read Mode. However, for the AD5282 dual-channel
device, the channel of interest is the one that is previously selected
in the Write Mode. In the case where users need to read the
RDAC values of both channels in 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 finally read
the second channel value in Read Mode again. Note that it is
not necessary for users to issue the Frame 3 data byte in Write
Mode for subsequent readback operation. Users should refer to
Figures 2 and 3 for the programming format.
ADDITIONAL PROGRAMMABLE LOGIC OUTPUT
AD5280/AD5282 features 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
the Write Mode (see Figure 2). These logic outputs have adequate
current driving capability to sink/source milliamperes of load.
Users can also activate O1 and O2 in three different ways without
affecting the wiper settings. They may do the following:
1. Start, Slave Address Byte, Acknowledge, Instruction Byte
with O1 and O2 specified, Acknowledge, Stop.
2. Complete the write cycle with Stop, then Start, Slave Address
Byte, Acknowledge, Instruction Byte with O1 and O2 specified,
Acknowledge, Stop.
3. Do 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
Shutdown can be activated by strobing the SHDN pin or pro-
gramming the SD bit in the Write Mode Instruction Byte. In
addition, shutdown can even be implemented with the device
digital output as shown in Figure 5. In this configuration, the
device will be shut down during power-up, but users are allowed
to program the device. Thus when O1 is programmed high, the
device will exit from Shutdown Mode and respond 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.
O1
SHDN
RPD
SDA
SCL
Figure 5. Shutdown by Internal Logic Output
MULTIPLE DEVICES ON ONE BUS
Figure 6 shows four AD5282 devices on the same serial bus.
Each has a different slave address since the states of their AD0
and AD1 pins 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.
MASTER
5V
RP RP
SDA SCL 5V SDA SCL 5V
AD1
AD1
AD0
AD5282
AD0
AD5282
SDA
SCL
SDA SCL 5V SDA SCL
AD1
AD1
AD0
AD5282
AD0
AD5282
Figure 6. Multiple AD5282 Devices on One Bus
LEVEL SHIFT FOR BIDIRECTIONAL INTERFACE
While most old systems may be operated at one voltage, a new
component may be optimized at another. When two systems
operate the same signal at two different voltages, proper level
shifting is needed. For instance, one can use a 3.3 V E2PROM
to interface with a 5 V digital potentiometer. A level shift scheme is
needed to enable a bidirectional communication so that the setting
of the digital potentiometer can be stored to and retrieved from
the E2PROM. Figure 7 shows one of the implementations.
M1 and M2 can be any N-Ch signal FETs or low threshold
FDV301N if VDD falls below 2.5 V.
VDD1 = 3.3V
RP
SDA1
SCL1
3.3V
E2PROM
RP G
S
D
M1
G
S
D
M2
VDD2 = 5V
RP RP
SDA2
5V
AD5282
SCL2
Figure 7. Level Shift for Different Potential Operation
LEVEL SHIFT FOR NEGATIVE VOLTAGE OPERATION
The digital potentiometer is popular in laser diode driver and
certain telecommunications equipment level-setting applications.
These applications are sometimes operated between ground
and some negative supply voltage such that the systems can be
biased at ground to avoid large bypass capacitors that may
significantly impede the ac performance. Like most digital
potentiometers, AD5280/AD5282 can be configured with a
negative supply (see Figure 8).
VDD
–5V
LEVEL SHIFTED
LEVEL SHIFTED
VSS
GND
SDA
SCL
Figure 8. Biased at Negative Voltage
REV. 0
–13–
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