AD7277ARMZ datasheet(22/29 Pages) AD

22 / 29 page

AD7276/AD7277/AD7278

Rev. C | 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)

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)

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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