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AD5253BRU100 Fiches technique(PDF) 25 Page - Analog Devices |
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AD5253BRU100 Fiches technique(HTML) 25 Page - Analog Devices |
25 / 32 page Data Sheet AD5253/AD5254 Rev. C | Page 25 of 32 D (Code in Decimal) 0 25 50 75 100 0 10 32 48 63 RWA RWB Figure 43. AD5253 RWA(D) and RWB(D) vs. Decimal Code Since the digital potentiometer is not ideal, a 75 Ω finite wiper resistance is present that can easily be seen when the device is programmed at zero scale. Because of the fine geometric and interconnects employed by the device, care should be taken to limit the current conduction between W and B to no more than ±5 mA continuous for a total resistance of 1 kΩ or a pulse of ±20 mA to avoid degradation or possible destruction of the device. The maximum dc current for AD5253 and AD5254 are shown in Figure 21 and Figure 22, respectively. Similar to the mechanical potentiometer, the resistance of the RDAC between Wiper W and Terminal A also produces a digitally controlled complementary resistance, RWA. When these terminals are used, the B terminal can be opened. The RWA starts at a maximum value and decreases as the data loaded into the latch increases in value (see Figure 43. The general equation for this operation is AD5253: RWA(D) = [(64 – D)/64] × RAB + 75 Ω (3) AD5254: RWA(D) = [(256 – D)/256] × RAB + 75 Ω (4) The typical distribution of RAB from channel-to-channel matches is about ±0.15% within a given device. On the other hand, device-to-device matching is process-lot dependent with a ±20% tolerance. PROGRAMMABLE POTENTIOMETER OPERATION If all three terminals are used, the operation is called potenti- ometer mode (see Figure 44); the most common configuration is the voltage divider operation. A B W VI VC Figure 44. Potentiometer Mode Configuration If the wiper resistance is ignored, the transfer function is simply AD5253: B AB W V V D V + × = 64 (5) AD5254: B AB W V V D V + × = 256 (6) A more accurate calculation that includes the wiper resistance effect is A W AB W AB N W V R R R R D D V 2 2 ) ( + + = (7) where 2N is the number of steps. Unlike in rheostat mode operation, where the tolerance is high, potentiometer mode operation yields an almost ratiometric function of D/2N with a relatively small error contributed by the RW terms. Therefore, the tolerance effect is almost cancelled. Similarly, the ratiometric adjustment also reduces the temperature coefficient effect to 50 ppm/°C, except at low value codes where RW dominates. Potentiometer mode operations include other applications such as op amp input, feedback-resistor networks, and other voltage- scaling applications. The A, W, and B terminals can, in fact, be input or output terminals, provided that |VA|, |VW|, and |VB| do not exceed VDD to VSS. |
Numéro de pièce similaire - AD5253BRU100 |
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Description similaire - AD5253BRU100 |
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