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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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MCP41010E/P датащи(PDF) 14 Page - Microchip Technology |
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MCP41010E/P датащи(HTML) 14 Page - Microchip Technology |
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14 / 32 page  MCP41XXX/42XXX DS11195C-page 14 2003 Microchip Technology Inc. 4.1 Modes of Operation Digital potentiometer applications can be divided into two categories: rheostat mode and potentiometer, or voltage divider, mode. 4.1.1 RHEOSTAT MODE In the rheostat mode, the potentiometer is used as a two-terminal resistive element. The unused terminal should be tied to the wiper, as shown in Figure 4-2. Note that reversing the polarity of the A and B terminals will not affect operation. FIGURE 4-2: Two-terminal or rheostat configuration for the digital potentiometer. Acting as a resistive element in the circuit, resistance is controlled by changing the wiper setting. Using the device in this mode allows control of the total resistance between the two nodes. The total measured resistance would be the least at code 00h, where the wiper is tied to the B terminal. The resistance at this code is equal to the wiper resistance, typically 52 Ω for the 10 k Ω MCP4X010 devices, 125Ω for the 50 kΩ (MCP4X050), and 100 k Ω (MCP4X100) devices. For the 10 k Ω device, the LSB size would be 39.0625Ω (assuming 10 k Ω total resistance). The resistance would then increase with this LSB size until the total measured resistance at code FFh would be 9985.94 Ω. The wiper will never directly connect to the A terminal of the resistor stack. In the 00h state, the total resistance is the wiper resis- tance. To avoid damage to the internal wiper circuitry in this configuration, care should be taken to ensure the current flow never exceeds 1 mA. For dual devices, the variation of channel-to-channel matching of the total resistance from A to B is less than 1%. The device-to-device matching, however, can vary up to 30%. In the rheostat mode, the resistance has a positive temperature coefficient. The change in wiper- to-end terminal resistance over temperature is shown in Figure 2-8. The most variation over temperature will occur in the first 6% of codes (code 00h to 0Fh) due to the wiper resistance coefficient affecting the total resis- tance. The remaining codes are dominated by the total resistance tempco RAB, typically 800 ppm/°C. 4.1.2 POTENTIOMETER MODE In the potentiometer mode, all three terminals of the device are tied to different nodes in the circuit. This allows the potentiometer to output a voltage propor- tional to the input voltage. This mode is sometimes called voltage divider mode. The potentiometer is used to provide a variable voltage by adjusting the wiper position between the two endpoints as shown in Figure 4-3. Note that reversing the polarity of the A and B terminals will not affect operation. FIGURE 4-3: Three terminal or voltage divider mode. In this configuration, the ratio of the internal resistance defines the temperature coefficient of the device. The resistor matching of the RWB resistor to the RAB resistor performs with a typical temperature coefficient of 1 ppm/°C (measured at code 80h). At lower codes, the wiper resistance temperature coefficient will dominate. Figure 2-3 shows the effect of the wiper. Above the lower codes, this figure shows that 70% of the states will typically have a temperature coefficient of less than 5 ppm/°C. 30% of the states will typically have a ppm/°C of less than 1. A B W MCP4XXXX Resistor A B W MCP4XXXX V1 V2 |
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