Data Sheet

AD7091

Rev. A | Page 13 of 20

To exit power-down mode and power up the AD7091, pull

CONVST high at any time. On the rising edge of CONVST, the

device begins to power up. The power-up time of the AD7091

is 100 µs. To start the next conversion, operate the interface as

described in the Normal Mode section.

POWER CONSUMPTION

The two modes of operation for the AD7091—normal mode

and power-down mode (see the Modes of Operation section for

more information)—produce different power vs. throughput

rate performances. Using a combination of normal mode and

power-down mode achieves the optimum power performance.

To achieve optimum static current consumption, SCLK should

be in burst mode and CS should idle high. Failure to adhere to

these guidelines results in increased static current.

Improved power consumption for the AD7091 can also be

Power Consumption in Normal Mode

current consumption for the part in normal operational mode is

367 μA (composed of 9.1 μA of static current and 357.9 μA of

dynamic current during conversion). The dynamic current con-

sumption is directly proportional to the throughput rate.

The following example calculates the power consumption of

the AD7091 when operating in normal mode with a 500 kSPS

throughput rate and a 3 V supply.

The dynamic conversion time contributes 537 μW to the overall

power dissipation as follows:

((500 kSPS/1 MSPS) × 357.9 μA) × 3 V = 537 μW

The contribution to the total power dissipated by the normal

mode static operation is

9.1 μA × 3 V = 27 μW

Therefore, the total power dissipated at 500 kSPS is

537 μW + 27 μW = 564 μW

Power Consumption Using a Combination of Normal

Mode and Power-Down Mode

A combination of normal mode and power-down mode

achieves the optimum power performance. This operation

can be performed at constant sampling rates of <10 kSPS.

Figure 22 shows the AD7091 conversion sequence using a

combination of normal mode and power-down mode with a

static current is 9.1 μA. The dynamic current is 357.9 μA at

1 MSPS. The current consumption during power-down mode

is 324 nA. A conversion takes typically 650 ns to complete, and

the AD7091 takes 100 μs to power up from power-down mode.

The dynamic conversion time contributes 5 μW to the overall

power dissipation as follows:

((5 kSPS/1 MSPS) × 357.9 μA) × 3 V = 5 μW

The contribution to the total power dissipated by the normal

mode static operation and the power-down mode is

(((100 μs + 650 ns)/200 μs) × 9.1 μA) × 3 V +

((99.4 μs/200 μs) × 324 nA) × 3 V = 14 μW

Therefore, the total power dissipated at 5 kSPS is

5 μW + 14 μW = 19 μW

99

μs

POWER-DOWN

100

μs

POWER-UP

650ns

CONVERSION

200

μs

CONVST

EOC

CS

SDO

DATA

NOTES

1. EOC IS THE END OF A CONVERSION.

Figure 22. Conversion Sequence with Normal Mode and Power-Down Mode, 5 kSPS Throughput