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AD5227BUJZ10-R2 Arkusz danych(PDF) 10 Page - Analog Devices |
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AD5227BUJZ10-R2 Arkusz danych(HTML) 10 Page - Analog Devices |
10 / 16 page AD5227 Rev. B | Page 10 of 1 6 THEORY OF OPERATION The AD5227 is a 64-position 3-terminal digitally controlled potentiometer device. It presets to a midscale at system power- on. When CS is enabled, changing the resistance settings is achieved by clocking the CLK pin. It is negative-edge triggered, and the direction of stepping is determined by the state of the U/D input. When the wiper reaches the maximum or the minimum setting, additional CLK pulses do not change the wiper setting. CS U/D CLK GND VDD 6-BIT UP/DOWN CONTROL LOGIC POR MIDSCALE WIPER REGISTER A W B AD5227 Figure 24. Functional Block Diagram B W A D0 D2 D1 D4 D5 D3 RS RS = RAB/64 RW RS RS RS RDAC UP/DOWN CTRL AND DECODE Figure 25. AD5227 Equivalent RDAC Circuit PROGRAMMING THE DIGITAL POTENTIOMETERS Rheostat Operation If only the W-to-B or W-to-A terminals are used as variable resistors, the unused terminal can be opened or shorted with W. This operation is called rheostat mode and is shown in Figure 26. A W B A W B A W B Figure 26. Rheostat Mode Configuration The end-to-end resistance, RAB, has 64 contact points accessed by the wiper terminal, plus the B terminal contact, assuming that RWB is used (see Figure 25). Clocking the CLK input steps, RWB by one step. The direction is determined by the state of U/D pin. The change of RWB can be determined by the number of clock pulses, provided that the AD5227 has not reached its maximum or minimum scale. ΔRWB can, therefore, be approximated as ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × ± = Δ W AB WB R R CP R 64 (1) where: CP is the number of clock pulses. RAB is the end-to-end resistance. RW is the wiper resistance contributed by the on-resistance of the internal switch. Since in the lowest end of the resistor string a finite wiper resistance is present, care should be taken to limit the current flow between W and B in this state to a maximum pulse current of no more than 20 mA. Otherwise, degradation or possible destruction of the internal switches can occur. Similar to the mechanical potentiometer, the resistance of the RDAC between the Wiper W and Terminal A also produces a digitally controlled complementary resistance, RWA. When these terminals are used, the B terminal can be opened or shorted to W. Similarly, ΔRWA can be approximated as () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + − ± = Δ W AB WA R R CP R 64 64 (2) Equations 1 and 2 do not apply when CP = 0. The typical distribution of the resistance tolerance from device to device is process lot dependent. It is possible to have ±20% tolerance. Potentiometer Mode Operation If all three terminals are used, the operation is called potentiometer mode. The most common configuration is the voltage divider operation as shown in Figure 27. A W B VI VC Figure 27. Potentiometer Mode Configuration |
Podobny numer części - AD5227BUJZ10-R2 |
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Podobny opis - AD5227BUJZ10-R2 |
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