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AD5112 Datasheet(PDF) 19 Page - Analog Devices
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AD5112 Datasheet(HTML) 19 Page - Analog Devices
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Rev. 0 | Page 19 of 28
THEORY OF OPERATION
The AD5110/AD5112/AD5114 digital programmable resistors
are designed to operate as true variable resistors for analog
signals within the terminal voltage range of GND < V
. The resistor wiper position is determined by the RDAC
register contents. The RDAC register acts as a scratchpad
register that allows unlimited changes of resistance settings.
The RDAC register can be programmed with any position
setting using the I
C interface. Once a desirable wiper position
is found, this value can be stored in the EEPROM memory.
Thereafter, the wiper position is always restored to that position
for subsequent power-up. The storing of EEPROM data takes
approximately 18 ms; during this time, the device is locked and
does not acknowledge any new command, thus preventing any
changes from taking place.
RDAC REGISTER AND EEPROM
The RDAC register directly controls the position of the digital
potentiometer wiper. For example, when the RDAC register is
loaded with 0x3F (128-taps), the wiper is connected to full scale
of the variable resistor. The RDAC register is a standard logic
register; there is no restriction on the number of changes
It is possible to both write to and read from the RDAC register
using the I
C interface (see Table 10).
The contents of the RDAC register can be stored to the
EEPROM using Command 1 (Table 10). Thereafter, the
RDAC register is always set at that position for any future
on-off-on power supply sequence. It is possible to read back
the data saved into the EEPROM with Command 6 in Table 10.
In addition, the resistor tolerance error is saved within the
EEPROM; this can be read back and used to calculate the end-
to-end tolerance, providing an accuracy of 0.1%.
Low Wiper Resistance Feature
The AD5110/AD5112/AD5114 include extra steps to achieve a
minimum resistance between Terminal W and Terminal A or
Terminal B. These extra steps are called bottom scale and top
scale. At bottom scale, the typical wiper resistance decreases
from 70 Ω to 45 Ω. At top scale, the resistance between
Terminal A and Terminal W is decreased by 1 LSB, and the
total resistance is reduced to 70 Ω. The extra steps are not equal
to 1 LSB and are not included in the INL, DNL, R-INL, and
C SERIAL DATA INTERFACE
The AD5110/AD5112/AD5114 have 2-wire I
serial interfaces. These devices can be connected to an I
as a slave device under the control of a master device. See
Figure 3 for a timing diagram of a typical write sequence.
The AD5110/AD5112/AD5114 support standard (100 kHz) and
fast (400 kHz) data transfer modes. Support is not provided for
10-bit addressing and general call addressing.
The 2-wire serial bus protocol operates as follows:
The master initiates data transfer by establishing a start
condition, which is when a high-to-low transition on the
SDA line occurs while SCL is high. The following byte is
the address byte, which consists of the 7-bit slave address
and an R/W bit. The slave device corresponding to the
transmitted address responds by pulling SDA low during
the ninth clock pulse (this is termed the acknowledge bit).
At this stage, all other devices on the bus remain idle while
the selected device waits for data to be written to, or read
from, its shift register.
If the R/W bit is set high, the master reads from the slave
device. However, if the R/W bit is set low, the master writes
to the slave device.
Data is transmitted over the serial bus in sequences of nine
clock pulses (eight data bits followed by an acknowledge
bit). The transitions on the SDA line must occur during
the low period of SCL and remain stable during the high
period of SCL.
When all data bits have been read or written, a stop
condition is established. In write mode, the master pulls
the SDA line high during the 10
clock pulse to establish
a stop condition. In read mode, the master issues a no
acknowledge for the ninth clock pulse (that is, the SDA line
remains high). The master brings the SDA line low before
clock pulse, and high during the 10
clock pulse to
establish a stop condition.
The AD5110/AD5112/AD5114 each have two different slave
address options available. See Table 9 for a list of slave addresses.
Table 9. Device Address Selection
C Device Address
AD511X1 BCPZ Y2
AD511X1 BCPZ Y2-1
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