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AD7278BUJZ-500RL7 Datasheet(PDF) 21 Page - Analog Devices |
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AD7278BUJZ-500RL7 Datasheet(HTML) 21 Page - Analog Devices |
21 / 28 page ![]() Data Sheet AD7276/AD7277/AD7278 Rev. D | Page 21 of 28 POWER VS. THROUGHPUT RATE Figure 29 shows the power consumption of the device in normal mode, in which the part is never powered down. By using the power-down mode of the AD7276/AD7277/AD7278 when not performing a conversion, the average power consump- tion of the ADC decreases as the throughput rate decreases. Figure 30 shows that as the throughput rate is reduced, the device remains in its power-down state longer, and the average power consumption over time drops accordingly. For example, if the AD7276/AD7277/AD7278 are operated in continuous sampling mode with a throughput rate of 200 kSPS and an SCLK of 48 MHz (VDD = 3 V) and the devices are placed into power- down mode between conversions, then the power consumption is calculated as follows. The power dissipation during normal operation is 12.6 mW (VDD = 3 V). If the power-up time is one dummy cycle, that is, 333 ns, and the remaining conversion time is 290 ns, then the AD7276/AD7277/AD7278 can be said to dissipate 12.6 mW for 623 ns during each conversion cycle. If the throughput rate is 200 kSPS, then the cycle time is 5 µs and the average power dissipated during each cycle is 623/5,000 × 12.6 mW = 1.56 mW. Figure 29 shows the power vs. throughput rate when using the partial power-down mode between conver- sions at 3 V. The power-down mode is intended for use with throughput rates of less than 600 kSPS, because at higher sampling rates, there is no power saving achieved by using the power-down mode. THROUGHPUT (kSPS) 0 3.0 7.4 2000 7.2 7.0 6.8 6.6 6.4 6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 200 400 600 800 1000 1200 1400 1600 1800 VARIABLE SCLK 50MHz SCLK Figure 29. Power vs. Throughput Normal Mode THROUGHPUT (kSPS) 0 0 8.0 1000 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 200 400 600 800 VDD = 3V Figure 30. Power vs. Throughput Partial Power-Down Mode |
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