The ingenious use software programming, composes the X9241 interior’s four 64 tap digital potentiometer a high resolution low cost the digital potentiometer
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The digital potentiometer (DCP) is specially the new integrated circuit which for the substitution tradition mechanical potentiometer, the variable resistor designs. It through I2C, SPI as well as the CS, U/D, INC three ways and the MCU connections, may realize the application program control adjustment, also has the push-button control way, thus realizes with the traditional mechanical potentiometer or the variable resistor same electric potential, the resistance regulation function special integrated circuit. Compares with the traditional mechanical potentiometer, the digital potentiometer has the digital adjustment, the long life, easy to assemble, the economical space, not the vibration influence and so on prominent merit, has been widely applied in the medical equipment, the instruments and meters, the industrial control, the computer, the domestic electric appliances, the handset, the digital product and so on each domain.
In some applications, like light emitting diode’s dynamic bias adjustment, the use digital potentiometer or the trimming DAC control voltage, has received the resolution, the connection, the cost limit. In order to solve this kind of problem, we in here will introduce that uses the low resolution (64 taps), low cost’s Intersil (Xicor) company I2C main line planned target potentiometer X9241 composes a high resolution (8001 taps) digital potentiometer’s solution.
Realizes the high resolution principle
Our supposition has three digital potentiometers, POT1 and POT2 is 64 tap DCP, POT3 is 128 tap DCP, POT1 and POT2 serve as POT3 VH and the VL establishment, and must guarantee that POT1 and POT2 are throughout “1″ the position gap, then exerts on POT3 on some 63 kind of different voltage gap. Theoretically, when POT3 127 and the next voltage gap’s tap between 0 beats when the special voltage tap, should also have an unnecessary tap location, but these taps are not unnecessary, their function may improve the output the linearity, because in the neighboring two voltage gap’s tap 0 and the tap 127 voltages is the same. Regarding 63 different gap each, also draws support from 127 different outputs, will have 8001 (63×127=8001) the different Vw output to be possible obtains between VH and VL. Figure 1 i.e. bright this concept.
How to use X9241 to realize the high resolution (8001 taps)
Intersil (Xicor) company’s X9241 four non-volatility digital potentiometer integration in a monolithic CMOS micro electric circuit, its function diagram like chart 2. X9241 contains four resistance arrays, each array contains 63 resistance units. Both have between each unit and two vertices may skid the unit visit tap spot. The glide unit’s controls in array seat by the user through the I2C main line. Each resistance array with a glide end counter register (WCR) and four 8 bit data registers relates in together, four data registers and the glide end counting check may read in directly by the user and read out. Glide end counter register’s content control slip end in resistance array position. Data register’s content may transmit the glide end counter register to establish the glide end position, the current glide end’s position may also transmit any with in it contacting data register. The glide end counter register is volatility, when on component electricity, glide end counter register automatic data input register 0 (R0) value. Four data register right and wrong volatility, if does not need to have time many kinds of establishment preservation in the application to the potentiometer, may serve as the general memory cell, uses for to preserve the system parameters or the user data.
The X9241 interior has a special mechanism, may connect one by one neighboring digital potentiometer. The permission reaches 253 different tap locations much (, when connects one by one completely DCP time). As shown in Figure 3, we (X9241 internal neighboring two DCP) establish contacts POT1 and POT2, is it provides VH with POT0 (to be possible to adjust), provides VL with POT3 (to be possible to adjust). Then we obtained like front have stated the principle same circuit diagram.
POT0 and POT3 are POT1-2 (POT1 and POT2 establish contacts later call law) to establish the terminal voltage. Must guarantee that POT1 and POT3 are throughout “1″ the position gap, then exerts on POT1-2 on some 63 kind of different voltage gap. Upward or moves downward when along with the POT1-2 glide end position to the vertex, POT0 and the POT3 position must when necessary make the adjustment. If the POT1-2 glide end increases to surpasses 127:00, then POT0 and POT3 will increase “1″, but the POT1-2 glide end will return to the tap 0. Similarly, when the POT1-2 glide end decreases to the tap below 0, POT0 and the POT3 glide end will reduce “1″, and establishes the POT1-2 tap to 127. This point, invites the reader in the procedure detailed list which when behind the understanding attaches pays attention.
X9241 is suitable extremely for this duty, because its interior happen to have four independent DCP, and has the neighboring DCP series connected mechanism, moreover it uses the I2C main line control interface, the tap location may in the software the direct change, but does not need through each middle position transformation.
Figure 4 is uses X9241U (49.37K, 49.38K, 49.32K, 49.24K) the component to carry on between the neighboring tap’s typical result which to the electric circuit the test obtains. The big chart expressed that each tap’s glide terminal voltage accounts for the footing voltage percentage, the illustration accounts for the footing voltage percentage for neighboring tap between resolution.
Uses X9241 to realize the high resolution software code
For the convenience understanding realizes the control detail, we provided the C language source code (code to provide by Xicor Corporation, we have made certain revision). The user only needs himself to compile again is suitable (in function name same procedure introduces unanimously) in the different monolithic integrated circuit’s I2C hardware interface function, joins the source code which in the application procedure we provide, in the simple calling program introduced 5 functions, may realize the DCP high resolution control conveniently.
Realizes the high resolution software source code about X9241, engineer may arrive at http://www.icbase. com/download/X9241.c downloads.
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