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參數(shù)資料
| 型號： | EVAL-AD5272SDZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 10/28頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD EVAL FOR AD5272 |
| 標準包裝： | 1 |
| 主要目的： | 數(shù)字電位器 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | AD5272 |
| 主要屬性： | 1 通道，1024 位置 |
| 次要屬性： | 2.7 ~ 5.5 V，5 ppm/°C，I²C |
| 已供物品： | 電路板，CD，器件，穩(wěn)壓器 |
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AD5272/AD5274
Data Sheet
Rev. D | Page 18 of 28
THEORY OF OPERATION
The AD5272 and AD5274 digital rheostats are designed to
operate as true variable resistors for analog signals within the
terminal voltage range of VSS < VTERM < VDD. The RDAC register
contents determine the resistor wiper position. The RDAC
register acts as a scratchpad register, which allows unlimited
changes of resistance settings. The RDAC register can be
programmed with any position setting using the I2C interface.
When a desirable wiper position is found, this value can be
stored in a 50-TP memory register. Thereafter, the wiper
position is always restored to that position for subsequent
power-up. The storing of 50-TP data takes approximately
350 ms; during this time, the AD5272/AD5274 is locked and
does not acknowledge any new command thereby preventing
any changes from taking place. The acknowledge bit can be
polled to verify that the fuse program command is complete.
The AD5272/AD5274 also feature a patented 1% end-to-end
resistor tolerance. This simplifies precision, rheostat mode, and
open-loop applications where knowledge of absolute resistance
is critical.
SERIAL DATA INTERFACE
The AD5272/AD5274 have 2-wire I2C-compatible serial inter-
faces. Each of these devices can be connected to an I2C bus as
a slave device under the control of a master device; see Figure 3
for a timing diagram of a typical write sequence.
The AD5272/AD5274 support standard (100 kHz) and fast
(400 kHz) data transfer modes. Support is not provided for
10-bit addressing and general call addressing.
The AD5272/AD5274 each has a 7-bit slave address. The five
MSBs are 01011 and the two LSBs are determined by the state
of the ADDR pin. The facility to make hardwired changes to
ADDR allows the user to incorporate up to three of these
devices on one bus as outlined in Table 11.
The 2-wire serial bus protocol operates as follows: The master
initiates a 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 next byte is the address byte, which consists
of the 7-bit slave address and a R/W bit. The slave device cor-
responding 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.
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 10th 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 then
brings the SDA line low before the 10th clock pulse, and then
high during the 10th clock pulse to establish a stop condition.
SHIFT REGISTER
For the AD5272/AD5274, the shift register is 16 bits wide, as
shown in Figure 2. The 16-bit word consists of two unused bits,
which should be set to zero, followed by four control bits and
10 RDAC data bits (note that for the AD5274 only, the lower
two RDAC data bits are don’t care if the RDAC register is read
from or written to), and data is loaded MSB first (Bit 15). The
four control bits determine the function of the software command
(Table 12). Figure 43 shows a timing diagram of a typical
AD5272/AD5274 write sequence.
The command bits (Cx) control the operation of the digital
potentiometer and the internal 50-TP memory. The data bits
(Dx) are the values that are loaded into the decoded register.
Table 11. Device Address Selection
ADDR
A1
A0
7-Bit I2C Device Address
GND
1
0101111
VDD
0
0101100
NC (No Connection)1
1
0
0101110
1
Not available in bipolar mode. VSS < 0 V.
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