参数资料
| 型号： | AD5251BRU1 |
| 厂商： | Analog Devices Inc |
| 文件页数： | 14/28页 |
| 文件大小： | 0K |
| 描述： | IC DCP DUAL 1K 64POS 14TSSOP |
| 标准包装： | 96 |
| 接片： | 64 |
| 电阻（欧姆）： | 1k |
| 电路数： | 2 |
| 温度系数： | 标准值 650 ppm/°C |
| 存储器类型： | 非易失 |
| 接口： | I²C（设备位址） |
| 电源电压： | 2.7 V ~ 5.5 V，±2.25 V ~ 2.75 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 14-TSSOP |
| 包装： | 管件 |
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Data Sheet
AD5251/AD5252
Rev. D | Page 21 of 28
THEORY OF OPERATION
The AD5251/AD5252 are dual-channel digital potentiometers
in 1 k, 10 k, 50 k, or 100 k that allow 64/256 linear
resistance step adjustments. The AD5251/AD5252 employ
double-gate CMOS EEPROM technology, which allows
resistance settings and user-defined data to be stored in the
EEMEM registers. The EEMEM is nonvolatile, such that
settings remain when power is removed. The RDAC wiper
settings are restored from the nonvolatile memory settings
during device power-up and can also be restored at any time
during operation.
The AD5251/AD5252 resistor wiper positions are determined
by the RDAC register contents. The RDAC register acts like a
scratch-pad register, allowing unlimited changes of resistance
settings. RDAC register contents can be changed using the
device’s serial I2C interface. The format of the data-words and
the commands to program the RDAC registers are discussed in
the I2C Interface Detail Description section.
The four RDAC registers have corresponding EEMEM memory
locations that provide nonvolatile storage of resistor wiper position
settings. The AD5251/AD5252 provide commands to store the
RDAC register contents to their respective EEMEM memory
locations. During subsequent power-on sequences, the RDAC
registers are automatically loaded with the stored value.
Whenever the EEMEM write operation is enabled, the device
activates the internal charge pump and raises the EEMEM cell
gate bias voltage to a high level; this essentially erases the current
content in the EEMEM register and allows subsequent storage
of the new content. Saving data to an EEMEM register consumes
about 35 mA of current and lasts approximately 26 ms. Because
of charge-pump operation, all RDAC channels may experience
noise coupling during the EEMEM writing operation.
The EEMEM restore time in power-up or during operation is
about 300 s. Note that the power-up EEMEM refresh time
depends on how fast VDD reaches its final value. As a result, any
supply voltage decoupling capacitors limits the EEMEM restore
time during power-up. For example, Figure 20 shows a power-
up profile of the VDD where there is no decoupling capacitor and
the applied power is a digital signal. The device initially resets
the measured RDACs to midscale before restoring the EEMEM
contents. By default, EEMEM is loaded at midscale until a new
value is loaded. The omission of the decoupling capacitors
should only be considered when the fast restoring time is
absolutely needed in the application. In addition, users should
issue a NOP Command 0 immediately after using Command 1
to restore the EEMEM setting to RDAC, thereby minimizing
supply current dissipation. Reading user data directly from
EEMEM does not require a similar NOP command execution.
In addition to the movement of data between RDAC and
EEMEM registers, the AD5251/AD5252 provide other shortcut
commands that facilitate programming, as shown in Table 11.
Table 11. Quick Commands
Command
Description
0
NOP.
1
Restore EEMEM content to RDAC. Users should
issue NOP immediately after this command to
conserve power.
2
Store RDAC register setting to EEMEM.
3
Decrement RDAC 6 dB (shift data bits right).
4
Decrement all RDACs 6 dB (shift all data bits right).
5
Decrement RDAC one step.
6
Decrement all RDACs one step.
7
Reset EEMEM contents to all RDACs.
8
Increment RDAC 6 dB (shift data bits left).
9
Increment all RDACs 6 dB (shift all data bits left).
10
Increment RDAC one step.
11
Increment all RDACs one step.
12 to 15
Reserved.
LINEAR INCREMENT/DECREMENT COMMANDS
The increment and decrement commands (10, 11, 5, and 6) are
useful for linear step-adjustment applications. These commands
simplify microcontroller software coding by allowing the
controller to send just an increment or decrement command to
the AD5251/AD5252. The adjustments can be directed to a
single RDAC or to all four RDACs.
±6 dB ADJUSTMENTS
(DOUBLING/HALVING WIPER SETTING)
The AD5251/AD5252 accommodate ±6 dB adjustments of
the RDAC wiper positions by shifting the register contents to
left/right for increment/decrement operations, respectively.
Command 3, Command 4, Command 8, and Command 9
can be used to increment or decrement the wiper positions in
6 dB steps synchronously or asynchronously.
Incrementing the wiper position by +6 dB essentially doubles
the RDAC register value, whereas decrementing the wiper
position by –6 dB halves the register content. Internally, the
AD5251/AD5252 use shift registers to shift the bits left and
right to achieve a ±6 dB increment or decrement. The maximum
number of adjustments is nine and eight steps for incrementing
from zero scale and decrementing from full scale, respectively.
These functions are useful for various audio/video level
adjustments, especially for white LED brightness settings in
which human visual responses are more sensitive to large
adjustments than to small adjustments.
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